The Temporal Bone and Transtemporal Approaches

CHAPTER 8

The Temporal Bone and Transtemporal Approaches

Albert L. Rhoton, Jr., M.D.Department of Neurological Surgery, University of Florida, Gainesville, Florida

Key words: Cranial base, Cranial nerves, Facial nerve, Internal carotid artery, Microsurgical anatomy, Skull base, Skull base neoplasm, Surgicalapproach, Temporal bone

The temporal bone is divided into squamosal, petrous,mastoid, tympanic, and styloid parts (Figs. 8.1 and 8.2).The squamosal part helps enclose the brain. The mas-

toid part is trabeculated and pneumatized to a variable de-gree and contains the mastoid antrum. The petrous part iscompact and encloses the cochlea, the vestibule, and the semi-circular, facial, and carotid canals (Fig. 8.3). The tympanic partforms part of the wall of the tympanic cavity and the externalacoustic meatus. The styloid projects downward and serves asthe site of attachment of several muscles. This section exam-ines these parts in greater detail and defines the anatomicbasis of the approaches directed through the temporal bone tothe posterior fossa and petroclival region. The approachesexamined are the middle fossa, translabyrinthine, transco-chlear, combined supra- and infratentorial presigmoid, sub-temporal anterior transpetrosal, subtemporal preauricular in-fratemporal, and the postauricular transtemporal approaches.

The approaches directed through the surface of the tempo-ral bone forming the middle fossa floor include 1) the verylimited middle fossa exposure of the internal acoustic meatus;2) the anterior petrosectomy approach directed medial to theinternal acoustic meatus through the petrous apex to accessthe upper anterior part of the posterior fossa and clivus; 3) theextended middle fossa approach, which may include not onlyresection of the roof of the internal acoustic meatus and pe-trous apex, but is extended lateral to the internal acousticmeatus to include resection, as needed, of the semicircularcanals, vestibule, roof of the mastoid antrum and tympaniccavity, and the posterior face of the temporal bone; and 4) thesubtemporal preauricular infratemporal fossa approach inwhich the middle fossa exposure is combined with exposureof the infratemporal fossa and, if needed, the petrous carotid,petrous apex, pterygopalatine fossae, and orbit.

The approaches directed through the mastoid in front of thesigmoid sinus vary in the amount of temporal bone resected.They include 1) the minimal mastoidectomy variant in whichonly enough presigmoid dura is exposed to open the dura infront of the sigmoid without exposing the labyrinth; 2) theretrolabyrinthine approach, which exposes the bony capsuleof the labyrinth; 3) the partial labyrinthectomy, which in-cludes removal of one or more of the semicircular canals; 4)the translabyrinthine approach, which includes resection of

the semicircular canals and vestibule; and 5) the transcochlearmodification, which includes removal of all the labyrinth,including the cochlear and possibly the petrous apex. Thesevariants of the transmastoid approaches can all be combined,as needed, with the supra- and infratentorial presigmoid ap-proaches to the middle and posterior fossa.

The final approach to be reviewed is the postauriculartranstemporal approach, which allows lesions involving themastoid, tympanic cavity, petrous apex, and jugular foramento be followed backward to the areas exposed by the retrosig-moid and far-lateral approaches and forward to the infratem-poral, pterygopalatine and middle fossae, lateral maxilla, andorbit. Selecting an approach directed through the temporalbone requires an understanding of its complex anatomy andits relationship to the petroclival region, the infratemporalfossa, and parapharyngeal space. Protecting and preservingthe facial nerve, the petrous carotid artery, and the sensoryorgans of the inner ear that are contained within the temporalbone are important elements in operative approaches directedthrough the lateral aspect of the cranial base.

THE TEMPORAL BONE ANDTRANSTEMPORAL APPROACHES

Lateral surface

When the skull and temporal bone are viewed from alateral perspective, some landmarks useful in performing ap-proaches directed around and through the temporal bone canbe identified (Fig. 8.2). The posterior end of the superiortemporal line continues inferiorly as the supramastoid crestand blends into the upper edge of the zygomatic arch. Thesupramastoid crest is located at the level of the floor ofthe middle fossa. The junction of the supramastoid crestwith the squamous suture is located at the lateral end of thepetrous ridge. The meeting point of the parietomastoid andsquamous sutures is located a few millimeters below the lateralend of the petrous ridge. The anterior edge of the junction of thesigmoid and transverse sinuses is located at the junction ofthe squamous and parietomastoid suture.

The mastoid antrum, a pneumatized space opening into thetympanic cavity, is located about 1.5 cm deep to the su-

S211Neurosurgery, Vol. 47, No. 3, September 2000 Supplement

FIGURE 8.1. Temporal bone. Aand B, inferior views. A, thetemporal bone has a squamosalpart, which forms some of thefloor and lateral wall of themiddle cranial fossa. It is also thesite of the mandibular fossa inwhich the mandibular condylesits. The tympanic part forms theanterior, lower, and part of theposterior wall of the externalcanal, part of the wall of thetympanic cavity, the osseousportion of the eustachian tube,and the posterior wall of themandibular fossa. The mastoidportion contains the mastoid aircells and mastoid antrum. Thepetrous part is the site of theauditory and vestibular labyrinth,the carotid canal, the internalacoustic meatus, and the facialcanal. The petrous part also formsthe anterior wall and the domeof the jugular fossa. The styloidpart projects downward andserves as the site of attachment ofthree muscles. B, inferior view ofthe temporal and surroundingbones. The squamosal andpetrous parts articulate anteriorlywith the greater wing of thesphenoid. The petrous apex facesthe foramen lacerum and isseparated from the clival part ofthe occipital bone by thepetroclival fissure. The occipitalbone joins with the petrous partof the temporal bone to form thejugular foramen. The mandibularfossa is located between theanterior and posterior roots of thezygomatic process. C and D,superior views. C, the medial partof the upper surface is the site of

the trigeminal impression in which Meckel’s cave sits. Farther laterally is the prominence of the arcuate eminence overlying thesuperior semicircular canal. Anterolateral to the arcuate eminences is the tegmen, a thin plate of bone overlying the mastoidantrum and epitympanic area. The temporal bone articulates anteriorly with the sphenoid bone, above with the parietal bone, andposteriorly with the occipital bone. The zygomatic process of the squamosal part has an anterior and a posterior root betweenwhich, on the lower surface, is located the mandibular canal. D, temporal and surrounding bones. The squamosal part of thetemporal bone joins anteriorly with the sphenoid bone to form the floor of the middle cranial fossa. Posteriorly, it articulates withthe occipital bone to form a portion of the anterior wall of the posterior fossa. Medially, it articulates with the clival portion of theoccipital bone at the petroclival fissure. The sigmoid sulcus descends along the posterior surface of the mastoid portion and turnsforward to enter the jugular foramen. The foramen lacerum is located at the junction of the temporal, sphenoid, and occipitalbones. The porus of the internal acoustic meatus is located in the central part of the posterior surface. Ac., acoustic; Ant., anterior;Arc., arcuate; Car., carotid; Cond., condyle; Digast., digastric; Emin., eminence; For., foramen; Gr., greater; Impress., impression;Int., internal; Jug., jugular; Mandib., mandibular; N., nerve; Occip., occipital; Pet., petrosal; Post., posterior; Proc., process; Sig.,sigmoid; Stylomast., stylomastoid; Trig., trigeminal; Tymp., tympanic.

S212 Rhoton

Neurosurgery, Vol. 47, No. 3, September 2000 Supplement

prameatal triangle, a depression in the mastoid surface lo-cated between the posterosuperior edge of the external me-atus, the supramastoid crest, and the vertical tangent alongthe posterior edge of the meatus. The suprameatal spine ofHenle is located at the outer end of the posterosuperior edgeof the external canal along the anterior edge of the su-prameatal triangle and corresponds to the level of the lateralsemicircular canal and tympanic segment of the facial nerve ata depth of approximately 1.5 cm. Several landmarks are alsohelpful in identifying the location of the junction of the trans-

verse and sigmoid sinuses at the posterior aspect of the mas-toid. The asterion located at the junction of the lambdoid,occipitomastoid, and parietomastoid sutures is usually lo-cated over the junction of the lower part of the transverse andsigmoid sinuses. A burr-hole placed at this site will usuallyexpose the lower edge of this junction. A burr-hole located atthe junction of the supramastoid crest and the squamosalsuture will be located at the posterior part of the middle fossafloor just above and anterior to the upper edge of the junctionof the transverse and sigmoid sinuses.

FIGURE 8.2. Temporal bone. A, posterior view of a right temporal bone. The squamosal part forms part of the floor and lat-eral wall of the middle fossa. The sigmoid sulcus descends along the posterior surface of the mastoid portion. The internalacoustic meatus enters the central portion of the petrous part of the bone. The trigeminal impression and arcuate eminenceare located on the upper surface of the petrous part. The vestibular aqueduct connects the vestibule in the petrous part withthe endolymphatic sac, which sits on the posterior petrous surface inferolateral to the internal acoustic meatus. B, enlargedview. The transverse crest separates the meatal fundus into a superior part where the facial canal and superior vestibularareas are situated, and an inferior part where the cochlear and inferior vestibular areas are located. The vertical crest sepa-rates the facial and superior vestibular areas. C, enlarged view of another internal acoustic meatus. The transverse crestdivides the meatal fundus into superior and inferior parts. The anterior part above the transverse crest is the site of the facialcanal and the posterior part is the site of the superior vestibular area. Below the transverse crest, the cochlear area is ante-rior and the inferior vestibular area is posterior. D, another internal acoustic meatus. The view is directed to expose the sin-gular foramen, for the singular branch of the inferior vestibular nerve that innervates the posterior ampullae. The inferior ves-tibular nerve also has a saccular and, occasionally, a utricular branch. Ac., acoustic; Arc., arcuate; CN, cranial nerve; Coch.,cochlear; Emin., eminence; Ext., external; For., foramen; Impress., impression; Inf., inferior; Int., internal; Mandib., mandibu-lar; Occipitomast., occipitomastoid; Parietomast., parietomastoid; Proc., process; Sig., sigmoid; Sp., spine; Sup., superior;Supramast., supramastoid; Trans., transverse; Trig., trigeminal; Vert., vertebral; Vest., vestibular.

Temporal Bone S213


The tympanic partThe tympanic part of the temporal bone is a curved plate

anterior to the mastoid process (Figs. 8.1, 8.2, and 8.4). Itsconcave posterior surface forms the anterior wall, floor,and part of the posterior wall of the external acousticmeatus. The roof and upper posterior wall are formed bythe squamosal part. Its surface contains a portion of thetympanic sulcus for attachment of the tympanic membrane,

which closes the medial end of the external canal. Theanterior surface, which is concave, forms the posterior wallof the mandibular fossa. Its lateral border forms most of themargin of the external acoustic meatus. Medially, it joinsthe petrous part at the petrotympanic fissure throughwhich the chorda tympani passes. The carotid canal andthe jugular foramen are located medial to the tympanicpart.

FIGURE 8.2. E, lateral view of the temporal bone. The squamosal part forms part of the lateral wall of the middle fossa, theposterior part of the zygomatic arch, and the upper part of the mandibular fossa. The tympanic part forms the posterior wall of themandibular fossa and almost all of the wall of the external canal. The styloid process is ensheathed at its base by the tympanic partand projects downward, serving as the attachment of several muscles. The mastoid part is located posteriorly and contains the mas-toid air cells that coalesce at the mastoid antrum. F, enlarged view of the external auditory canal. The spine of Henley, an excellentlandmark for locating the deep site of the lateral canal and tympanic segment of the facial nerve, is located along the posterosupe-rior margin of the external canal. The mastoid antrum is located deep to the depressed area, called the suprameatal triangle,located behind the spine of Henley. The view into the canal exposes the tympanic cavity, which has the promontory overlying thebasal turn of the cochlea and the oval and round windows in its medial wall. G, lateral surface of the temporal bone in the intactskull. The tympanic part forms the anterior and lower and part of the posterior wall of the external canal. The mandibular fossa isformed above and anteriorly by the squamosal part and behind by the tympanic part. The mastoid antrum is located posterosupe-rior to the spine of Henley, between the spine of Henley and the anterior part of the supramastoid crest. The asterion, the junctionof the lambdoid, parietomastoid, and occipital mastoid sutures, is usually located over the lower half of the junction of the sigmoidand transverse sinuses. The midpoint of the parietal mastoid suture is usually located at the anterior margin of the junction of thetransverse and sigmoid sinuses, and the lateral edge of the petrous ridge is located at the junction of the squamosal suture and thesupramastoid crest. H, the supra- and infratentorial areas have been exposed while preserving the bone at the site of the sutures.The asterion, located at the junction of the lambdoid, occipitomastoid, and parietomastoid sutures, overlies the lower half of thejunction of the transverse and sigmoid sinuses. The junction of the supramastoid crest and the squamosal suture is located at theposterior edge of the middle fossa and slightly anterior and above the junction of the transverse and sigmoid sinuses.

S214 Rhoton


The styloid process, a slender spicule ensheathed by theinferior border of the tympanic bone, projects into the infra-temporal fossa and is the site of attachment for the styloglos-sus, stylopharyngeus, and stylohyoid muscles (Fig. 8.5). It is

located immediately anterior to the emergence of the facialnerve from the stylomastoid foramen and is covered laterallyby the parotid gland. The stylomastoid foramen, the externalend of the facial canal, opens between the styloid and mastoid

FIGURE 8.3. A–D. Posterior surface of the temporal bone. A, the internal meatus is located near the center and the jugularforamen at the lower edge of the posterior surface. The sigmoid sinus descends along the posterior surface of the mastoidand turns forward on the occipital bone to pass through the sigmoid part of the jugular foramen. The inferior petrosal sinusdescends along the petroclival fissure and passes through the petrosal part of the jugular foramen. The subarcuate fossa islocated superolateral and the ostium for the vestibular aqueduct lateral to the internal acoustic meatus. The trigeminalimpression is a shallow trough on the upper surface of the temporal bone behind the foramen ovale. The arcuate eminenceoverlies the superior semicircular canals. B, temporal bone with the nerves preserved. The abducens nerve ascends to enterDorello’s canal. The trigeminal nerve passes above the petrous apex to enter the porus of Meckel’s cave. The facial and ves-tibulocochlear nerves enter the internal acoustic meatus, and the glossopharyngeal, vagus, and accessory nerves enter thejugular foramen. The posterior and superior semicircular canals have been exposed. C, enlarged view. The upper end of theposterior canal and the posterior end of the superior canal share the common crus. The endolymphatic duct extends down-ward from the vestibule and opens into the endolymphatic sac located beneath the dura inferolateral to the meatus. Theendolymphatic ridge, the bridge of bone forming the posterior lip of the vestibular aqueduct, has been preserved. The jugularbulb can be seen through the thin bone below the internal meatus. D, enlarged view of the fundus of the meatus afterremoval of the posterior wall. The upper edge of the porus has been preserved. The subarcuate artery enters the subarcuatefossa. The inferior vestibular nerve gives rise to the singular branch to the posterior ampullae, plus utricular and saccularbranches. The superior vestibular nerve innervates the ampullae of the superior and lateral semicircular canals and commonlygives rise to a utricular branch. A., artery; Ac., acoustic; Arc., arcuate; Car., carotid; CN, cranial nerve; Coch., cochlear;Emin., eminence; Endolymph., endolymphatic; Fiss., fissure; For., foramen; Hypogl., hypoglossal; Impress., impression; Inf.,inferior; Int., internal; Intermed., intermedius; Jug., jugular; Lat., lateral; N., nerve; Nerv., nervus; Pet., petrosal, petrous; Pet-rocliv., petroclival; Post., posterior; Semicirc., semicircular; Sig., sigmoid; Subarc., subarcuate; Sup., superior; Trig., trigemi-nal; Vest., vestibular.

Temporal Bone S215


processes. The facial nerve crosses the lateral surface of thestyloid process, and the external carotid artery crosses the tip.Resecting the styloid process and reflecting the attached mus-cles downward exposes the internal jugular vein as it exits thejugular foramen and the carotid artery as it enters the carotidcanal medial to the tympanic bone.

The squamous part

The externally convex surface of the squamosal part givesattachment to the temporalis muscle (Figs. 8.1, 8.2, and 8.5).

The supramastoid crest extends backward across its posteriorpart, giving attachment to the temporalis muscle and fascia.The suprameatal triangle, a depressed area, located below theanterior part of the crest and behind the posterosuperiormargin of the external meatus, marks the deep location of themastoid antrum. The cerebral surface of the squamosal part isconcave, accommodating the temporal lobe and joining thegreater wing of the sphenoid anteriorly. The zygomatic pro-cess of the squamosal part projects forward and with thezygomatic bone completes the zygomatic arch. The attach-

FIGURE 8.3. E–H. Posterior surface of the temporal bone. E, the petrous apex medial to the internal acoustic meatus hasbeen removed to expose the petrous carotid. The lateral genu of the petrous carotid, located at the junction of the verticaland horizontal segments of the petrous carotid, is situated below and medial to the cochlea. The jugular bulb extends upwardtoward the vestibule and semicircular canals adjacent to the posterior meatal wall. The inferior petrosal sinus courses alongthe petroclival fissure and enters the petrosal part of the jugular foramen, and the sigmoid sinus descends in the sigmoidgroove and enters the sigmoid part of the foramen. The glossopharyngeal, vagus, and accessory nerves pass through the cen-tral or intrajugular part of the foramen between the sigmoid and petrosal parts. F, bone has been removed along the anteriormargin of the meatal fundus to open the cochlea, and along the posterior margin to expose the vestibule. The jugular bulbextends upward toward the semicircular canals and vestibule. G, enlarged view. The cochlear nerve penetrates the modiolusof the cochlea where its fibers are distributed to the turns of the cochlear duct. The basal turn of the cochlea communicatesbelow the modiolus with the vestibule. H, enlarged view of the vestibule and cochlea. The stapes has been removed from theoval window. The promontory in the medial wall of the tympanic cavity is located lateral to the basal turn of the cochlea. Asilver fiber has been introduced into the superior canal, a red fiber into the lateral canal, and a blue fiber into the posteriorcanal. The ampullated ends are located at the bulbous ends of the three fibers. The common crus of the superior and poste-rior canals is located at the site where the tips of the blue and silver fibers overlap. The superior vestibular nerve passes tothe ampullae of the superior and lateral canals. The singular branch of the inferior vestibular nerve innervates theposterior ampullae. A small black fiber has been introduced into the opening of the endolymphatic duct into the vestibule.

S216 Rhoton


ment of the zygomatic process to the squama is wide giving itanterior and posterior edges, referred to as the anterior andposterior roots. The temporalis fascia attaches to the supe-rior border of the arch and the masseter attaches to the lowerborder. The posterior root of the zygomatic process blendsposteriorly into the suprameatal crest. The anterior root islocated at the anterior margin of the temporomandibularjoint, with the joint forming a rounded fossa on the lowermargin of the zygomatic process between the anterior andposterior roots. The upper margin of the zygomatic processbetween the two roots gives attachment to the posterior partof the temporalis muscle. The mandibular fossa, located onthe lower margin of the process between the two roots, isdelimited in front by the articular tubercle and posteriorly bythe postglenoid tubercle adjacent to its junction with thetympanic bone. The squamotympanic fissure is located be-tween the medial part of the squamosal part of the mandib-ular fossa and the medial part of the tympanic bone. Thepetrotympanic fissure is situated between the tympanic plateand the petrosal part and leads into the tympanic cavity; itcontains the anterior ligament of the malleus and the anteriortympanic branch of the maxillary artery. The anterior canal-iculus for the chorda tympani exits the tympanic cavity in thepetrotympanic fissure. The rootlets of the temporal branch ofthe facial nerve cross the lateral aspect of the zygomatic archand course through the subcutaneous tissues on the superfi-cial layer of the temporal fascia. During resection of the zy-gomatic arch, the superficial temporalis fascia should be care-fully dissected from the underlying deep fascia, starting asclose as possible to the tragal cartilage, and carried forward,reflecting the superficial fascia anteriorly to avoid damage tothe filaments of the temporal branch to the frontalis muscle.

The mastoid part

The mastoid is the posterior part of the temporal bone (Figs.8.1, 8.2, and 8.4). It projects downward to form the processthat is the site of attachment, from superficial to deep, of thesternocleidomastoid, splenius capitis and longissimus capitismuscles, and the posterior belly of the digastric muscle (Fig.8.5). The lower surface medial to the mastoid process isgrooved by the mastoid notch to which the posterior belly ofthe digastric attaches. Medial to the notch, the occipitalgroove gives passage to the occipital artery. The fascia cover-ing the anterior margin of the posterior belly of the digastricis continuous anteriorly with the connective tissue surround-ing the emergence of the mastoid segment of the facial nervefrom the stylomastoid foramen and can be used as a landmarkfor identifying the initial extracranial segment of the nerve.After exiting the stylomastoid foramen, the nerve divides inthe substance of the parotid gland into temporal, zygomatic,buccal, marginal mandibular, and cervical branches (Fig. 8.5).The temporal and zygomatic branches cross the zygomaticarch and the superficial fascia of the temporalis muscle. Keep-ing the connective tissue surrounding the nerve at the stylo-mastoid foramen intact during mobilization of the facial nervewill reduce the risk of facial nerve damage. The posteriorborder of the mastoid process is perforated by one or more

foramina through which an emissary vein to the sigmoidsinus and a dural branch from the occipital artery pass.

The medial aspect of the mastoid process is grooved by thesigmoid sinus (Figs. 8.1-8.4). The sinus represents the poste-rior limit of the mastoid cavity. The sinus meets the roof of thecavity at the level of the petrous ridge. The angle betweenthe superior petrosal and sigmoid sinuses and the middlefossa dura delimits a dural space called the sinodural angle.The sinodural angle is an important landmark when exposingthe contents of the mastoid. Inferiorly, the sigmoid sinuscurves medially and forward, crossing the occipital bone toenter the jugular foramen. The superior aspect of the jugularforamen corresponds to the apex of the jugular bulb andconstitutes the inferior limit of the mastoid cavity.

The medial limit of the mastoid cavity is formed by theblock of solid bone, the otic capsule, containing the bonylabyrinth (Figs. 8.4 and 8.6). The area of posterior fossa duramater that can be exposed through the mastoid cavity be-tween the sigmoid and superior petrosal sinuses, the oticcapsule, and the jugular bulb is called Trautman’s triangle.The size of this dural triangle is important in surgical proce-dures in which the dura delimited by the triangle must beopened medial to the sigmoid sinus. The distance from theanterior margin of the sigmoid sinus to the otic capsule atthe level of the posterior semicircular canal averages 8 mm(range, 6–9 mm) on the right side, and 7 mm (range, 4–9 mm)on the left (44).

The distance between the apex of the jugular bulb and thesuperior petrosal sinus is also an important determinate of thesize of exposure that can be achieved by opening Trautman’striangle. This distance is reduced if there is a high jugularbulb. The jugular bulb usually lies inferior to the ampulla ofthe posterior semicircular canal, but it can project superiorlyas far as the level of the lateral semicircular canal (27). Theaverage distance from the jugular bulb to the superior petro-sal sinus is 14 mm (range, 10–19 mm) on the right side, and 16mm (range, 11–21 mm) on the left (44).

The mastoid interior is composed of trabeculated bone,which coalesces to form a cavity, the mastoid antrum, thatcommunicates through an opening, the aditus, that leadsforward to the epitympanic part of in the tympanic cavity(Figs. 8.4 and 8.6). The lateral semicircular canal is medial tothe epitympanic recess. The medial wall of the antrum facesthe posterior semicircular canal. The roof is formed by thetegmen in the floor of the middle cranial fossa. The mastoidsegment of the facial canal courses adjacent to the anteroin-ferior margin of the antrum. The lateral wall of the mastoidantrum, through which it is usually approached surgically, isformed by the postmeatal part of the squamous temporalbone. The lateral wall of the antrum is located deep to thesuprameatal triangle, which is demarcated superiorly bythe suprameatal crest, located at the level of the floor of themiddle fossa; anteroinferior by the posterosuperior margin ofthe acoustic meatus, which indicates approximately the posi-tion of the descending or mastoid part of the facial canal; andposteriorly by a posterior vertical tangent to the posteriormargin of the external meatus. The air cells in the mastoidmay extend behind the sigmoid sinus and into the squamosal

Temporal Bone S217


FIGURE 8.4. Tympanic cavity and mastoid antrum. A, the tympanic bone forms the anterior, lower, and part of the posteriorwall of the external canal. The facial nerve exits the skull through the stylomastoid foramen, which is located medial to thetympanomastoid suture. The spine of Henley approximates the deep site of the tympanic facial segment and the lateral canal.The mastoid antrum is located between the posterosuperior wall of the external canal and middle fossa floor deep to thedepression behind the spine of Henle. B, a mastoidectomy has been completed to expose the capsule of the posterior and lat-eral canals and the tympanic and mastoid facial segments. C, the posterior and superior wall of the external canal and thetympanic membrane have been removed while preserving the malleus and chorda tympani. The mastoid segment of the facialnerve descends through the facial canal and gives rise to the chorda tympani, which passes upward and forward across thetympanic membrane and malleus neck. D, enlarged view. The head of the incus articulates with the head of the malleus, theshort process of the incus points backward toward the facial nerve, and the long process attaches to the stapes, which sits inthe oval window. The stapedial muscle passes forward below the tympanic segment of the facial nerve and attaches to theneck of the stapes. E, the incus has been removed to expose the stapes sitting in the oval window. The chorda tympani

S218 Rhoton


part of the temporal bone, the posterior root of the zygomaticprocess, the osseous roof of the external acoustic meatus, thefloor of the tympanic cavity near the jugular bulb, and thepetrous apex surrounding the carotid canal, eustachian tube,and labyrinth.

The tympanic cavity is a narrow air-filled space betweenthe tympanic membrane laterally and the promontory con-taining the auditory and vestibular labyrinth medially (Figs.8.4, 8.6, and 8.7). It communicates posteriorly with the mas-toid antrum and anteriorly through the eustachian tube withthe nasopharynx. It contains the malleus, incus, and stapes.The tympanic cavity opens upward into the epitympanicrecess, which contains the heads of the malleus and the incus.The roof of the tympanic cavity is formed by a thin plate, thetegmen tympani, which separates the middle fossa and tym-panic cavities, and also roofs the mastoid antrum and thetensor tympani. The thin floor of the tympanic cavity sepa-rates the cavity from the jugular bulb. The medial part of thefloor is perforated by an opening for the tympanic branchof the glossopharyngeal nerve. The lateral wall is formedby the tympanic membrane and the osseous ring to whichthe membrane attaches. The ring is deficient above near theopenings of the anterior and posterior canaliculi for thechorda tympani (Figs. 8.4 and 8.6). The posterior canalicu-lus for the chorda tympani arises from the facial canal a fewmillimeters above the mastoid foramen and ascends infront of the facial canal to open into the tympanic cavity atthe level of the upper part of the handle of the malleus. Thechorda tympani passes in close relation to the tympanicmembrane and the medial aspect of the neck of the malleusand forward to enter its anterior canaliculus at the medialaspect of the petrotympanic fissure, and descends verticallymedial to the sphenoid spine and lateral pterygoid muscleto join the lingual nerve.

The medial wall of the tympanic cavity, which forms thelateral boundary of the inner ear and the petrosal part of thetemporal bone, is the site of the promontory, the oval andround windows, and the prominence over the facial nerve(Figs. 8.2 and 8.4). The tympanic nerve plexus grooves thepromontory overlying the lateral bulge of the basal turn ofthe cochlea. The apex of the cochlea lies near the medial wallof the cavity anterior to the promontory. The oval window isposterosuperior to the promontory and connects the tympaniccavity to the vestibule, and is occupied by the footplate of the

stapes. The round window is posteroinferior to the oval win-dow and opens under the overhanging edge of the promon-tory. The prominence of the facial canal is located above theoval window. The posterior wall of the tympanic cavity ismainly the site of the aditus, the opening of the tympaniccavity, into the mastoid antrum. The medial wall of the aditushas a round prominence overlying the lateral semicircularcanal. The pyramidal eminence, which houses the stapedialmuscle, is located just behind the oval window and anterior tothe mastoid part of the facial canal. The stapedius extendsforward from the eminence to attach to the neck of the stapes.The fossa incudis is a small depression low and posterior inthe epitympanic recess; it contains the short process of theincus, which is fixed to the fossa by ligamentous fibers.

The anterior wall of the tympanic cavity narrows and leadsinto the eustachian tube, which communicates the nasophar-ynx with the tympanic cavity (Figs. 8.4, 8.7, and 8.8). It hasbony and cartilaginous parts. The bony part begins in theanterior part of the tympanic cavity and is directed anteriorlyand medially. It joins the cartilaginous part at the junction ofthe squamous and petrous parts of the temporal bone. Thecartilaginous part of the tube is attached to the lower marginof the sphenopetrosal groove, which is situated between thepetrous bone and the greater wing of the sphenoid bone, andits base lies directly under the mucous membrane of thelateral wall of the nasaopharynx. Both the petrous carotid andeustachian tube are directed anteromedially, with the eusta-chian tube being located along the anterior margin of thecarotid canal (Figs. 8.7 and 8.8). The tensor tympani muscleand its bony semicanal are located above the eustachian tube,parallel to the horizontal segment of the petrous carotid. Thecanals for the tensor tympani superiorly and the osseous partof the eustachian tube inferiorly open into the upper part ofthe anterior wall of the tympanic cavity. These canals areinclined downward, anteriorly, and medially; they open intothe angle between the squamous and petrous parts of thetemporal bone and are separated by a thin, bony septum. Thecanal for the tensor tympani extends posterolaterally on themedial wall of the tympanic cavity, to end above the ovalwindow where the posterior end of the canal curves laterallyto form a pulley, the trochleariform process, around which thetensor tympani tendon turns laterally to attach to the handleof the malleus.

Š

crosses the neck of the malleus. The promontory is located superficial to the basal turn of the cochlea. The labyrinth and fun-dus of the internal meatus are located medial to the tympanic cavity. A line directed medially through the skull along thelong axis of the external meatus will also approximate the site of the long axis of the internal meatus on the medial side ofthe promontory and acousticovestibular labyrinth. F, the stapes has been removed from the oval window. The handle of themalleus attaches to the tympanic membrane, the neck is crossed by the chorda tympani, and the head articulates with theincus, which has been removed. The tendon of the tensor tympani attaches to the upper part of the handle of the malleus.The stapedial muscle is housed within the pyramidal eminence and its tendon inserts on the stapedial neck. Chor., chorda;CN, cranial nerve; Emin., eminence; Endolymph., endolymphatic; Epitymp., epitympanic; Eust., eustachian; Jug., jugular; Lat.,lateral; Long., longus; M., muscle; Mast., mastoid; Memb., membrane; N., nerve; Post., posterior; Proc., process; Seg., seg-ment; Sig., sigmoid; Sp., spine; Squamomast., squamomastoid; Temp., temporal; Tymp., tympani, tympanic; Tympanomast.,tympanomastoid.

Temporal Bone S219


FIGURE 8.5. A–F. Muscular and osseous relationships. A, the skin and subcutaneous tissues have been removed to expose theparotid gland and the facial nerve branches that course deep to the parotid gland on their way to the facial muscles. Themasseter muscle has two heads: a more superficial anterior head, which passes downward to the lateral surface of the angleof the jaw, and a deeper posterior head, which arises from the medial surface of the zygomatic arch and passes to the man-dibular body. The sternocleidomastoid attaches to the lateral part of the superior nuchal line and mastoid process, descendsin an anterior direction, and is crossed by the greater auricular nerve. The temporalis fascia attaches to the upper surface ofthe zygomatic arch. The trapezius muscle attaches to the medial part of the superior nuchal line. The posterior triangle of theneck, located between the sternocleidomastoid and trapezius, has the semispinalis capitis, splenius capitis, and levator scapu-lae in its floor. The terminal branches of the occipital artery and the greater occipital nerve reach the subcutaneous tissuesby passing between the attachment of the trapezius and sternocleidomastoid muscles to the superior nuchal line. B, enlargedview. The facial nerve branches are exposed along the anterior edge of the parotid gland. C, the parotid gland has beenremoved to expose the facial nerve and its branches distal to the stylomastoid foramen. The nerve passes lateral to the styloid

S220 Rhoton


The petrous part

The petrous part of the temporal bone is wedged betweenthe sphenoid and occipital bones (Figs. 8.1 and 8.3). It containsthe acoustic and vestibular labyrinth and is the site of thejugular fossa and the facial and carotid canals (Figs. 8.3, 8.4,and 8.7). It has a base, apex, three surfaces and margins. Theapex is located in the angle between the greater wing of thesphenoid and the occipital bone and is the site of the carotidcanals medial opening. It forms the posterolateral limit of theforamen lacerum. The anterior surface faces the floor ofthe middle cranial fossa and its surface is grooved by thetrigeminal impression for the trigeminal ganglion; anterolat-eral to this, it forms the roof of the carotid canal (Figs. 8.1 and8.7). Lateral to the trigeminal impression is a shallow depres-sion, which partially roofs the internal acoustic meatus and islimited laterally by the arcuate eminence, which overlies thesuperior semicircular canal. The posterior slope of the arcuateeminence overlies the posterior and lateral semicircular ca-nals. Farther laterally, the roof covers the vestibule and part ofthe facial canal. The tegmen extends laterally from here androofs the mastoid antrum and tympanic cavities and the canalfor the tensor tympani. Opening the tegmen from above ex-poses the heads of the malleus, incus, the tympanic segmentof the facial nerve, and the superior and lateral semicircularcanals (Fig. 8.7). The tympanic segment of the facial nervebegins at the geniculate ganglion and ends at the level of thestapes, where the nerve turns downward below the lateralsemicircular canal. The tegmen anteriorly is grooved by thegreater petrosal nerve extending anterior and medial fromthe area in front of the arcuate imminence and crossing thefloor of the middle fossa toward the foramen lacerum (Figs.

8.7 and 8.8). The greater petrosal nerve can be identifiedmedial to the arcuate eminence as it leaves the geniculateganglion by passing through the facial hiatus to reach themiddle fossa floor. It runs beneath the dura of the middlefossa in the sphenopetrosal groove formed by the junction ofthe petrous and sphenoid bones, immediately superior andanterolateral to the horizontal segment of the petrous carotid.In a previous study, we found that bone of the middle cranialfossa was absent over the geniculate ganglion in 16% of thespecimens, thus exposing the facial nerve and geniculate gan-glion to the danger of injury during elevation of the dura fromthe floor of the middle fossa (31). Facial nerve injury can alsoresult from damaging the branch of the middle meningealartery, which passes through the facial hiatus to supply thenerve, or from traction applied to the ganglion when manip-ulating the greater petrosal nerve (30).

The lesser petrosal nerve from the tympanic plexus passesthrough the tympanic canaliculus, which is located anterior tothe facial hiatus and courses in an anteromedial directionparallel to the greater petrosal nerve (Fig. 8.8). The cochlea liesbelow the floor of the middle fossa in the angle between thelabyrinthine segment of the facial nerve and the greater petro-sal nerve, just medial to the geniculate ganglion, anterior tothe fundus of the internal acoustic meatus, and posterosupe-rior to the lateral genu of the petrous carotid artery. Thecochlea is separated from the petrous carotid by a 2.1 mm(range, 0.6–10.0 mm) thickness of bone and can be injuredduring exposure of the petrous carotid. The middle meningealartery, an important landmark when approaching the struc-tures of the middle fossa, enters the cranial cavity through theforamen spinosum of the sphenoid bone. The foramen spino-

Š

process, the external carotid artery, and mandibular neck. The superficial and deep heads of the masseter muscle areexposed. This lower end of the sternocleidomastoid muscle has been reflected posteriorly by dividing its attachment to theclavicle and sternum. The superficial temporal artery ascends in front of the ear. D, the upper part of the mandibular ramusand the lower part of the temporalis muscle and its attachment to the coronoid process have been removed while preservingthe inferior alveolar nerve. The infratemporal fossa is located medial to the mandible and on the deep side of the temporalismuscle. The upper and lower heads of the lateral pterygoid, which insert along the temporomandibular joint, and the superfi-cial head of the medial pterygoid, which extends from the lateral pterygoid plate to the angle of the jaw, have been exposed.The structures in the infratemporal fossa include the pterygoid muscles, branches of the mandibular nerve, the maxillaryartery, and the pterygoid venous plexus. The sternocleidomastoid muscle has been reflected out of the exposure to exposethe splenius capitis muscle. E, posterolateral view. The splenius capitis has been reflected downward to expose the longissi-mus capitis, superior oblique, and semispinalis capitis. The occipital artery passes along the occipital groove on the medialside of the digastric groove. F, the longissimus capitis has been reflected downward to expose the rectus capitis posteriorminor and major, which descend from the occipital bone to attach to the spinous process of C1 and C2, respectively; thesuperior oblique, which passes from the occipital bone to the transverse process of C1; and the inferior oblique, whichextends from the spinous process of C2 to the transverse process of C1. The vertebral artery, in its ascent from C2 to C1, isexposed medial to the attachment of the levator scapulae to the C1 transverse process. The C1 transverse process is situatedimmediately behind the internal jugular vein and a short distance below and behind the jugular foramen. A., artery; Alv.,alveolar; Ant., anterior; Aur., auricular; Brs., branches; Cap., capitis; Car., carotid; CN, cranial nerve; Cond., condyle; Constr.,constrictor; Eust., eustachian; Ext., external; Gl., gland; Gr., greater; Inf., inferior; Int., internal; Jug., jugular; Lat., lateral;Lev., levator; Long., longus; Longiss., longissimus; M., muscle; Maj., major; Mandib., mandibular; Max., maxillary; Med., medi-al; Memb., membrane; Min., minor; N., nerve; Obl., oblique; Occip., occipital; Pal., palatini; Parapharyng., parapharyngeal;Pet., petrosal; Post., posterior; Proc., process; Pteryg., pterygoid; Pterygopal., pterygopalatine; Rec., rectus; Scap., scapula;Semispin., semispinalis; Splen., splenius; Sternocleidomast., sternocleidomastoid; Suboccip., suboccipital; Sup., superior;Superf., superficial; Temp., temporal, temporalis; Tens., tensor; TM., temporomandibular; Trans., transverse; Tymp., tympanic;V., vein; Veli./Vel., veli; Vert., vertebral.

Temporal Bone S221


FIGURE 8.5. G–L. Muscular and osseous relationships. G, the mandibular condyle and ramus have been removed to expose the styloidprocess and attached muscles. The pterygoid muscles and some branches of the mandibular nerve have been removed to expose the auri-culotemporal nerve, which splits into two roots that surround the middle meningeal artery. The levator veli palatini, which attaches thelower margin of the eustachian tube, is in the medial part of the exposure. The longus capitis is exposed medial to the internal carotidartery in the retropharyngeal area. H, the muscles that attach to the styloid process have been divided at their origin. The facial nervecrosses the lateral surface of the styloid process. The attachment of the tensor veli palatine to the skull base extends between the foramenovale and the eustachian tube. I, the external auditory canal has been removed, but the tympanic membrane and cavity have been pre-served. The levator veli palatine and part of the tensor veli palatine have been removed and the membranous part of the eustachian tubeopened. The eustachian tube crosses anterior to and is separated from the petrous carotid by a thin shell of bone. The jugular bulb andlateral bend of the petrous carotid are located below the osseous labyrinth. The pterygopalatine fossa is exposed anteriorly. J, the eusta-chian tube has been resected and the mandibular nerve divided at the foramen ovale to expose the petrous carotid. This exposes the lon-gus capitis and rectus capitis anterior, both of which are located behind the posterior pharyngeal wall. K, the petrous carotid has beenreflected forward out of the carotid canal to expose the petrous apex medial to the carotid canal. L, the petrous apex and upper clivushave been drilled and the dura opened to expose the anterolateral aspect of the pons below the trigeminal nerve. The sigmoid sinus andthe jugular bulb have been removed to expose the nerves exiting the jugular foramen.

S222 Rhoton


sum is an average of 4.5 mm (range, 3–6 mm) anterolateral tothe carotid canal and 14.0 mm (range, 11.0–17.0 mm) antero-lateral to the geniculate ganglion (44).

The posterior surface of the petrosal part faces the posteriorcranial fossa and cerebellopontine angle and is continuous

with the mastoid surface (Figs. 8.1-8.3). The opening for theinternal auditory meatus is situated midway between the baseand the apex on the posterior surface. The lateral end of themeatus is divided into superior and inferior halves by thetransverse crest. The area above the transverse crest is further

FIGURE 8.6. A–D. Translabyrinthine exposure. A, the insert shows the site of the exposure directed through the mastoid. Thespine of Henley at the posterosuperior margin of the external meatus is a superficial landmark that approximates the deepsite of the lateral semicircular canal and the tympanic segment of the facial nerve. The mastoidectomy has been completed.The superior petrosal and sigmoid sinuses, the jugular bulb, and the facial nerve are usually skeletonized in the approach,leaving a thin layer of bone over them. The semicircular canals, which are located in the cortical bone medial to the cancel-lous mastoid and the mastoid antrum, have been exposed. The dura between the sigmoid and superior petrosal sinuses, thejugular bulb, and the labyrinth, which faces the cerebellopontine angle, is referred to as Trautman’s triangle. B, the mastoidantrum opens through the aditus into the epitympanic part of the tympanic cavity, which contains the upper part of the mal-leus and incus. The tympanic segment of the facial nerve passes between the lateral canal and the stapes in the oval windowand then turns downward as the mastoid segment. The chorda tympani arises from the mastoid segment of the facial nerveand passes upward and forward along the deep surface of the tympanic membrane crossing the neck of the malleus. Theincus, the head of which is located in the epitympanic area, has a long process that attaches to the stapes. C, the semicircularcanals and vestibule have been removed and the dura lining the internal acoustic meatus has been opened to expose the ves-tibulocochlear nerve. D, the dura has been opened to expose the petrosal cerebellar surface and the structures in the cer-ebellopontine angle. Anatomic variants that limit the exposure include an anterior position of the sigmoid sinus, a high jugu-lar bulb, or a low middle fossa plate. The jugular bulb may extend upward into the posterior wall of the internal acousticmeatus and be encountered as the posterior meatal wall is being removed by either the translabyrinthine or retrosigmoidapproaches. Ac., acoustic; A.I.C.A., anteroinferior cerebellar artery; Chor., chorda; CN, cranial nerve; Coch., cochlear; Inf.,inferior; Int., internal; Intermed., intermedius; Jug., jugular; Laby., labyrinthine; Lat., lateral; Mast., mastoid; N., nerve; Nerv.,nervus; Pet., petrosal; P.I.C.A., posteroinferior cerebellar artery; Post., posterior; Seg., segment; Sig., sigmoid; Sup., superior;Tymp., tympani, tympanic; V., vein; Vest., vestibular.

Temporal Bone S223


divided by the vertical crest, also called Bill’s bar, whichseparates the anteriorly located facial canal from the posteri-orly located superior vestibular area (29). The cochlea andinferior vestibular nerves penetrate the lateral end of themeatus below the transverse crest, with the cochlear nervebeing located anteriorly. The posterior wall of the meatus,lateral to the porus is the site of a small bony opening, thesubarcuate fossa, which gives passage to the subarcuate ar-tery, a branch of the anteroinferior cerebellar artery (AICA),which usually ends blindly in the region of the superiorsemicircular canal. Inferolateral to the porus of the meatus isthe opening for the vestibular aqueduct, which transmits theendolymphatic duct that opens below into the endolymphatic

sac located between the dural layers. The opening of thecochlear aqueduct, also called the cochlear canaliculus andoccupied by the perilymphatic duct, is situated inferior to theporus of the internal meatus at the anteromedial edge of thejugular foramen, just superior and lateral to where the glos-sopharyngeal nerve enters the intrajugular part of the jugularforamen.

The inferior surface is very irregular. The apex is connectedmedially to the clivus by fibrocartilage and gives attachmentto the levator veli palatini and the cartilaginous portion of theeustachian tube (Figs. 8.1 and 8.9). Behind this is the openingof the carotid canal, behind which is the jugular fossa thatcontains the jugular bulb. The small foramen for the tympanic

FIGURE 8.6. E–H.Translabyrinthine exposure. E,enlarged view of the exposurein the cerebellopontine angle.In this case, theglossopharyngeal and vagusnerves can be seen, although,in the translabyrinthineexposure, the jugular bulboften obstructs the view of thenerves entering the jugularforamen. F, thevestibulocochlear nerve hasbeen elevated to expose thefacial nerve. G, thelabyrinthine, tympanic, andmastoid segments of the facialnerve have been exposed inpreparation for transposition ofthe nerve for a transcochlearapproach. H, the facial nervehas been transposed backwardand the bone anterior to themeatal fundus has beenremoved to expose the cochleafor a transcochlear approach inwhich the cochlea is removedto gain access to the side ofthe clivus and front of thebrainstem. The cochlear nervehas been divided. The cochlearfibers innervating the cochlearduct pass through themodiolus.

S224 Rhoton


branch of the glossopharyngeal nerve is located on the ridgebetween the carotid canal and jugular foramen (Fig. 9.2). Onthe lateral wall of the jugular bulb is the mastoid canaliculusfor the auricular branch of the vagus nerve. The superiorborder, located along the petrous ridge, is grooved by thesuperior petrosal sinus and serves as the attachment ofthe tentorium cerebelli, except medially where it is crossed bythe posterior trigeminal root. The lower posterior border,located along the petroclival fissure, is the site of a groove in

which resides the inferior petrosal sinus that connects thecavernous sinus and the medial wall of the jugular bulb.Behind this, the jugular fossa of the temporal bone joins withthe jugular notch on the jugular process of the occipital boneto form the margins of the jugular foramen.

The jugular foramen is located at the lower end of thepetro-occipital fissure and is divided into a larger lateralopening, the sigmoid part, that receives the drainage of thesigmoid sinus, and a small medial part, the petrosal part, that

FIGURE 8.7. A–D. Middle fossa exposure of the temporal bone. A, superolateral view. The tentorium, except the edge, hasbeen removed. The dura has been removed from the middle fossa floor and cavernous sinus wall to expose the greater petro-sal nerve, middle meningeal artery, and the nerves in the sinus wall. B, the middle fossa floor has been opened to expose thecochlea, semicircular canals, petrous carotid artery, and the facial, cochlear, and superior vestibular nerves in the meatus.The superior canal bulges upward into the middle fossa below the arcuate eminence. The cochlear nerve passes below thefacial nerve to enter the cochlea, which is located above the lateral genu of the petrous carotid in the angle between the pre-geniculate facial and greater petrosal nerves. C, another temporal bone drilled to expose the internal acoustic meatus,cochlea, vestibule, semicircular canals, tympanic cavity, and external meatus. The vestibule is located posterolateral andthe cochlea is anteromedial to the fundus of the internal meatus. The vestibule communicates below the meatal funduswith the cochlea. The tensor tympani muscle and eustachian tube are layered along, but are separated from, the anterior sur-face of the petrous carotid by a thin layer of bone. The tegmen has been opened to expose the head of the incus and malleusin the epitympanic area. The internal acoustic meatus lies directly medial to, but is separated from, the external meatus bythe tympanic cavity and the labyrinth. D, the nerves in the meatus have been separated to expose the superior and inferiorvestibular, facial, and cochlear nerves. A., artery; Ac., acoustic; A.I.C.A., anteroinferior cerebellar artery; Car., carotid; CN,cranial nerve; Coch., cochlear; Eust., eustachian; Ext., external; Gang., ganglion; Genic., geniculate; Gr., greater; Inf., inferior;Lat., lateral; M., muscle; Men., meningeal; Mid., middle; N., nerve; Pet., petrosal, petrous; Post., posterior; S.C.A., superiorcerebellar artery; Sup., superior; Tens., tensor; Tent., tentorial; Tymp., tympani, tympanic; Vert., vertebral; Vest., vestibular.

Temporal Bone S225


transmits the inferior petrosal sinus (Fig. 9.1). The intrajugularpart, located between the sigmoid and petrosal parts, trans-mits the glossopharyngeal, vagus, and accessory nerves. Theanterior border is joined laterally to the temporal squama atthe petrosquamosal suture and medially articulates with thesphenoid’s greater wing.

The bony labyrinth consists of three parts: the vestibule, thesemicircular canals, and the cochlea. The vestibule, located inthe central part of the bony labyrinth, is a small cavity at theconfluence of the ampullate and nonampullated ends of thesemicircular canals. It is situated lateral to the meatal fundus,medial to the tympanic cavity, posterior to the cochlea, andsuperior to the apex of the jugular bulb (Figs. 8.3, 8.4, and 8.7).

The floor of the vestibule is separated from the apex of thejugular bulb by a thickness of bone that averages 6 mm(range, 4–8 mm) on the right side and 8 mm (range, 4–10 mm)on the left side (44). This distance is particularly importantduring translabyrinthine approaches since the height of thejugular bulb is a major determinant of the size of the exposureof the cerebellopontine angle that can be achieved with thisapproach. A high-placed jugular bulb may be the source oftroublesome bleeding and air emboli if it is opened duringexposure of the labyrinth or internal acoustic meatus.

The semicircular canals are situated posterosuperior to thevestibule (Figs. 8.3, 8.4, and 8.7). The anterior part of the lateralsemicircular canal is situated above the tympanic segment of

FIGURE 8.7. E–H. Middle fossa exposure of the temporal bone. E, enlarged view. The vestibule, into which the semicircularcanals open, communicates below the meatal fundus with the cochlea. The vertical crest, often called Bill’s bar, separates thesuperior vestibular and facial nerves at the meatal fundus. The tendon of the tensor tympani makes a right-angle turn aroundthe trochleariform process in the medial margin of the tympanic cavity to insert on the malleus. F, enlarged view. The supe-rior canal projects upward in the floor of the middle fossa. The lateral canal is situated above the tympanic segment of thefacial nerve in the posteromedial part of the epitympanic area, and the posterior canal is located lateral to the posterior wallof the internal acoustic meatus. G, bone has been removed below the greater petrosal nerve to expose the petrous carotid.The tensor tympani muscle above and the eustachian tube below are layered along the anterior surface of the petrouscarotid. H, enlarged view. Suture has been placed in the three semicircular canals. The anterior end of the superior and lat-eral canals and the lower end of the posterior canal are the site of the ampullae. The posterior end of the superior canal andthe upper end of the posterior canal join to form a common crus. The facial and superior vestibular nerves have beenremoved to expose the cochlear and inferior vestibular nerves. The singular branch of the inferior vestibular nerve innervatesthe posterior ampullae. The superior vestibular nerve innervates the superior and lateral ampullae.

S226 Rhoton


the facial nerve and can be used as a guide to locating thatsegment of the nerve. The posterior semicircular canal liesparallel to and in close proximity with the posterior surface ofthe petrous bone in the area just behind and lateral to thelateral end of the internal acoustic meatus. The superior semi-circular canal projects toward the floor of the middle fossa,usually in close relation to the arcuate eminence. Each canalhas an ampullated and a nonampullated end that opens intothe vestibule. The anterior end of the lateral and superiorcanals and the inferior end of the posterior canal are the site ofthe ampullae, which are innervated by the vestibular nerves.The posterior ends of the superior and posterior canals, theends opposite the ampullae, join to form a common crus thatopens into the vestibule. The superior vestibular nerve inner-vates the ampullae of the superior and lateral canals, and thesingular branch of the inferior vestibular nerve innervatesthe posterior ampulla. The vestibular nerves also havebranches to the utricle and saccule located within the vesti-bule. The internal auditory meatus can be found medial to thearcuate eminence at an angle of about 60 degrees medial fromthe long axis of the superior semicircular canal. The superiorcanal is the most susceptible to damage in completing themiddle fossa approach to the internal acoustic meatus. The

posterior canal may be damaged in removing the posteriorwall to expose the meatal contents by the retrosigmoid ap-proach (Fig. 8.3).

During surgical approaches to the cerebellopontine angle inwhich the posterior meatal lip is removed, care should betaken to avoid opening the vestibular aqueduct, vestibule,posterior semicircular canal, or the common crus (Figs. 8.2 and8.3). In our studies, we observed that there is a constant set ofrelationships among the structures around the posteriormeatal lip. The common crus of the posterior and superiorsemicircular canals is located lateral to the entrance of thesubarcuate artery into the subarcuate fossa. The vestibularaqueduct has an oblique orientation. It leaves the vesti-bule and runs in a posterior direction to open beneath thedura mater at a level corresponding to that of the posteriorsemicircular canal. The average distance between the poste-rior semicircular canal, at the level with the junction of thecommon crus, and the lateral edge of the porus was 7 mm(range, 5–9 mm) (44).

The carotid artery, at the point where it enters the carotidcanal, is surrounded by a strong layer of connective tissue thatmakes it difficult to mobilize the artery at this point (Figs. 8.9

FIGURE 8.8 A, superior view of the temporal bone andinfratemporal fossa and orbit. The floor of the middle fossa hasbeen removed to expose the temporalis muscle in the temporalfossa and the pterygoid muscles and branches of the thirdtrigeminal division in the infratemporal fossa. The posterior partof the middle fossa forming the upper surface of thetemporomandibular joint has been removed to expose themandibular condyle. The internal acoustic meatus extendslaterally from the posterior surface of the temporal bone. Themastoid is located behind the external canal and lateral to thesemicircular canals and vestibule. B, enlarged view. Thetrigeminal nerve has been reflected forward and bone has beenremoved over the eustachian tube, tensor tympani muscle,petrous carotid, and internal acoustic meatus. Dura has beenremoved from the lateral wall of the cavernous sinus to exposethe trochlear, trigeminal, and oculomotor nerves in the sinuswall and the abducens nerve passing below the petrosphenoidligament and through Dorello’s canal. The greater petrosalnerve is joined by the deep petrosal branches of the carotidsympathetic plexus to form the vidian nerve, which passesforward in the vidian canal, which has been unroofed. Thelesser petrosal nerve arises from the tympanic branch of theglossopharyngeal nerve, which passes across the promontory inthe tympanic nerve plexus and regroups to cross the floor of themiddle fossa, exiting the skull to provide parasympatheticinnervation through the otic ganglion to the parotid gland. Thetensor tympani muscle and eustachian are layered along, butare separated from, the anterior surface of the petrous carotidby a thin layer of bone. A., artery; Car., carotid; Cav.,cavernous; Chor., chorda; CN, cranial nerve; Cond., condyle;Eust., eustachian; Gang., ganglion; Gen., geniculate; Gr.,greater; Lat., lateral; Less., lesser; Lig., ligament; M., muscle;

Mandib., mandibular; Max., maxillary; N., nerve; Ophth., ophthalmic; Pet., petrosal, petrous; Pteryg., pterygoid; Semicirc.,semicircular; Sphen., sphenoid; Temp., temporal; Tens., tensor; Tymp., tympani, tympanic.

Temporal Bone S227


FIGURE 8.9. Inferior views of anaxial section of the skull base. A, theinfratemporal fossa is surrounded bythe maxillary sinus anteriorly, themandible laterally, the sphenoidpterygoid process anteromedially,and the parapharyngeal spaceposteromedially, and contains themandibular nerve and maxillaryartery and their branches, themedial and lateral pterygoidmuscles, and the pterygoid venousplexus. B, part of the lateralpterygoid muscle has been removedto expose the branches of thetrigeminal nerve coursing in theinfratemporal fossa below thegreater sphenoid wing. Thepterygopalatine fossa is locatedbetween the posterior maxillary wallanteriorly, the sphenoid pterygoidprocess posteriorly, the nasal cavitymedially, and the infratemporal fossalaterally. The pharyngeal recess(fossa of Rosenmuller) projectslaterally from the posterolateralcorner of the nasopharynx with itslateral apex facing the internalcarotid artery laterally and theforamen lacerum above. Theposterior nasopharyngeal wall isseparated from the lower clivus andthe upper cervical vertebra by thelongus capitis, and thenasopharyngeal roof rests against theupper clivus and the posterior partof the sphenoid sinus floor. C, thesphenoid pterygoid process has beenremoved to expose the maxillarynerve passing through the foramenrotundum to enter thepterygopalatine fossa where it givesrise to the infraorbital nerve, whichcourses in the roof of the maxillarysinus. The maxillary nerve within thepterygopalatine fossa gives off com-

municating rami to the pterygopalatine ganglion. The vidian nerve, formed by the union of the deep petrosal nerve from the ca-rotid sympathetic plexus and the greater petrosal nerve, courses forward through the vidian canal to join the pterygopalatine gan-glion. The terminal part of the petrous carotid is exposed above the foramen lacerum. D, enlarged view with highlighting of thepre- (red ) and poststyloid (yellow) compartments of the parapharyngeal space. The styloid diaphragm, formed by the anterior partof the carotid sheath, separates the parapharyngeal space into pre- and poststyloid parts. The prestyloid compartment, a narrowfat-containing space between the medial pterygoid and tensor veli palatini, separates the infratemporal fossa from the medially lo-cated lateral nasopharyngeal region containing the tensor and levator veli palatini and the eustachian tube. The poststyloid compartment,located behind the prestyloid part, contains the internal carotid artery, internal jugular vein, and the cranial nerves IX through XII. A.,artery; Cap., capitis; Car., carotid; CN, cranial nerve; Cond., condyle; Eust., eustachian; For., foramen; Gl., gland; Gr., greater; Infraorb.,infraorbital; Infratemp., infratemporal; Int., internal; Jug., jugular; Lat., lateral, lateralis; Lev., levator; Long., longus; M., muscle; Mandib.,mandibular; Max., maxillary; N., nerve; Nasolac., nasolacrimal; Occip., occipital; Pal., palatini; Parapharyng., parapharyngeal; Proc., pro-cess; Pteryg., pterygoid; Pterygopal., pterygopalatine; Rec., rectus; Tens., tensor; V., vein; Vel., veli.

S228 Rhoton


and 8.10) (38, 39). The vertical segment of the artery passesupward in the canal toward the genu, where it curvesanteromedially to form the horizontal segment. The eusta-chian tube and the tensor tympani muscle are located par-allel to and along the anterior margin of the horizontalsegment, where they are separated from the artery by a thinlayer of bone.

The trigeminal ganglion and the adjacent part of the poste-rior root and their surrounding dural and arachnoidal cavern,called Meckel’s cave, sit in an impression on the upper surfaceof the petrous apex above the medial part of the petrouscarotid (Figs. 8.1, 8.7, and 8.8). The length of the horizontalsegment of the petrous carotid that can be exposed by remov-

ing bone lateral to the trigeminal ganglion averages 8.1 mm(range, 4.0–11.0 mm) (44). The length that can be exposed canbe increased if the mandibular branch of the trigeminal nerveis retracted or divided, after which the average length that canbe exposed increases to 20.1 mm (range, 17.5–28.0 mm) (Figs.8.7 and 8.8) (10, 17). Gaining this added exposure can beparticularly helpful during surgical procedures that are di-rected through the petrous apex to complete a vascular anas-tomosis, to occlude the artery for control of bleeding, and toallow for mobilization of the vertical and horizontal segmentsof the artery (40). A venous plexus of variable size, an exten-sion of the cavernous sinus within the periosteal covering ofthe distal part of the canal, surrounds the artery.

FIGURE 8.10. A–D. Preauricularsubtemporal-infratemporal fossaapproach. A, the scalp flap hasbeen reflected forward. The flapis positioned so that a neckdissection as well as afrontotemporal craniotomy canbe completed. The scalp flap hasbeen reflected forward whileprotecting the facial nerve and itsbranches. The neck dissection hasbeen completed below theparotid gland. The facial nervebranches passing deep to theparotid have been preserved. B,the dissection has been carriedaround the parotid gland toexpose the branches of the facialnerve. The internal jugular veinand internal carotid artery areexposed below the gland. C, theparotid gland has been removedto expose the branches of thefacial nerve distal to thestylomastoid foramen. D, asegment of the mandibular ramushas been removed, leavingthe mandibular condyle in themandibular fossa, to expose themaxillary artery and pterygoidmuscles in the infratemporalfossa. Branches of the thirdtrigeminal division pass betweenthe lateral and medial pterygoidmuscles. The inferior alveolarnerve descends to enter theinferior alveolar foramen andcanal.

Temporal Bone S229


The facial nerve in the temporal bone, which often blocksaccess to lesions within and deep to the temporal bone, isdivided into three segments (Figs. 8.4, 8.5, and 8.7). The first,or labyrinthine segment, which is located in the petrous part,extends from the meatal fundus to the geniculate ganglionand is situated between the cochlea anteromedially and thesemicircular canals posterolaterally. The labyrinthine segmentends at the site at which the greater superficial petrosal nervearises from the facial nerve at the level of the geniculateganglion. From there, the nerve turns laterally and posteriorlyalong the medial surface of the tympanic cavity, thus givingthe name tympanic segment to that part of the nerve. Thetympanic segment runs between the lateral semicircular canalabove and the oval window below. As the nerve passes belowthe midpoint of the lateral semicircular canal, it turns verti-cally downward and courses through the petrous part adja-cent to the mastoid part of the temporal bone; thus the thirdsegment, which ends at the stylomastoid foramen, is calledthe mastoid or vertical segment.

Petroclival region

These transtemporal operative approaches are often di-rected to the petroclival region located where the posteriorsurface of the petrous temporal bone meets the clival part ofthe occipital bone along the petroclival fissure. The junction ofthe two bones forms a line that extends from the jugularforamen to the petrous apex (Fig. 8.1). From a surgical stand-

point, the intradural compartments of the petroclival regionare divided along this petroclival line into 1) an inferior spacerelated to the medulla and to the structures around the re-gion of the foramen magnum; 2) a middle space related to thepons and to the structures in the prepontine and cerebel-lopontine angle; and 3) a superior space related to the con-tents of the interpeduncular cistern, and to the sellar andparasellar regions.

The inferior petroclival spaceThe inferior petroclival space corresponds to the anterior sur-

face of the medulla and adjacent part of the clivus and anteriormargin of the foramen magnum (4). The neurovascular struc-tures in this region are those contained in the premedullarycistern. The superior limit is the junction of the pons and me-dulla. The inferior limit is the rostral margin of the first cervicalnerve root, the site of the junction of the spinal cord and themedulla. The inferior petroclival space includes the lower fourcranial nerves, lower part of the cerebellum, the vertebral arteryand its branches, and the structures around the occipital condyle.

The middle petroclival spaceThe middle petroclival space corresponds to the anterolat-

eral surface of the pons and cerebellum. Its superior limit is atthe pontomesencephalic sulcus and the lower limit is at thepontomedullary sulcus. The lateral limits are formed by theposterior surface of the petrous bone and by the contents of

FIGURE 8.10. E, a frontotemporal craniotomy has been completed and the dura of the lateral wall of the cavernoussinus has been elevated. In addition, the lateral orbital wall has been removed to expose the globe, extraocular muscles,and lacrimal gland. F, enlarged view of the region of the cavernous sinus. The PCA and SCA have been exposed coursingabove and below the oculomotor and trochlear nerves, respectively. The optic nerve is exposed above the internalcarotid artery. An opening has been made into the lateral wall of the sphenoid sinus between the first and seconddivisions. The maxillary nerve passes forward to join the terminal branches of the maxillary artery in the pterygopalatinefossa. The maxillary nerve continues forward along the floor of the orbit as the infraorbital nerve. The superior ophthalmicvein descends across the origin of the lateral rectus muscle and enters the anterior portion of the cavernous sinus. A., artery;A.I.C.A., anteroinferior cerebellar artery; Alv., alveolar; Bas., basilar; Brs., branches; Cap., capitis; Car., carotid; Cav., cavern-ous; CN, cranial nerve; Ext., external; Front., frontal; Gl., gland; Inf., inferior; Infraorb., infraorbital; Int., internal; Jug., jugu-lar; Lac., lacrimal; Lat., lateral; Long., longus; M., muscle; Max., maxillary; Med., medial; N., nerve; Ophth., ophthalmic;P.C.A., posterior cerebral artery; Pet., petrosal, petrous; Pteryg., pterygoid; Pterygopal., pterygopalatine; Rec., rectus; S.C.A.,superior cerebellar artery; Sphen., sphenoid; Submandib., submandibular; Sup., superior; Temp., temporal; Tens., tensor; TM.,temporomandibular; Tymp., tympani; V., vein; Vert., vertebral.

S230 Rhoton


the cerebellopontine angle including the trigeminal, abdu-cens, facial, and vestibulocochlear nerves, the basilar artery,and the AICA and the superior petrosal veins.

The superior petroclival spaceThe superior petroclival space is located anterior to the

midbrain and corresponds to the anterior part of the tentorialincisura. It extends anteriorly and laterally to the sellar andparasellar regions. Its roof is formed by the diencephalicstructures forming the floor of the third ventricle. The poste-rior limit is formed by the cerebral peduncles and the posteriorperforated substance. The inferior limit is situated above theorigin of the trigeminal nerve at the pontomesencephalic sulcus.It includes the intradural segment of the oculomotor and troch-lear nerves, the basilar artery and its branching into the posterior

cerebral artery (PCA) and superior cerebellar artery (SCA), andthe cavernous carotid and its intracavernous branches to thedura of the upper clivus. The medial edge of the tentoriumdivides the superior petroclival space into infra- and supraten-torial compartments.

Adjacent structures

The structures important in accessing the temporal bonefrom posteriorly and laterally have already been reviewed. Thissection reviews the structures located in front of the temporalbone that are important in reaching lesions that involve the boneor involve both the bone and areas anterior to it. They includeseveral muscles, like the temporalis and masseter, the infratem-poral fossa, and the parapharyngeal spaces.

FIGURE 8.10. G–J.Preauricular subtemporal-infratemporal fossa approach.G, the floor of the middle fossahas been resected back to thelevel of the tensor tympanimuscle and eustachian tube,and the petrous carotid artery.The nerves exiting the jugularforamen and hypoglossal canalpass laterally between theinternal carotid artery andinternal jugular vein to reachtheir end organs. H, theeustachian tube and tensortympani have been resectedand the bone lateral to theforamen ovale removed. Thisexposes the full length of thepetrous carotid. I, the petrouscarotid has been reflectedforward out of the carotidcanal to expose the petrousapex medial to the jugularforamen and lateral wall of theclivus. J, the petrous apex andadjacent part of the clivusmedial to the jugular foramenand cochlea have beenremoved and the dura openedto expose the junction of thevertebral and basilar arteriesand the origin of the AICA.

Temporal Bone S231


The temporalis muscle, along with the deep temporal ves-sels, passes between the gap formed by the zygomatic archand the floor of the temporal fossa (Fig. 8.5). The muscleattaches to the coronoid process of the mandible. The super-ficial and the deep temporalis fasciae attach, respectively, tothe lateral and medial aspects of the upper border of thezygomatic arch. Inferiorly, the parotid fascia invests the pa-rotid gland and the masseter muscle and attaches to the lowerborder of the zygomatic arch. The masseter muscle has twosuperimposed layers. A superficial layer which attaches to thezygomatic process of the maxilla and anterior part of thelower border of the zygomatic arch and a deep layer whichattaches to the medial aspect of the whole zygomatic arch.Inferiorly it inserts onto the angle and ramus of the mandible.

The parotid gland, the parotid duct, and the branches of thefacial nerve are located superficial to the masseter muscle(Figs. 8.5, 8.9, and 8.10). In surgical procedures in which themandibular condyle is resected or displaced inferiorly, theparotid gland, along with the branches of the facial nerve, canbe dissected from the underlying masseter to avoid excessivetraction on the facial nerve and to reduce the risk of facialpalsy (33).

Muscles commonly encountered in operative approaches tothe region of the temporal bone include the posterior belly ofthe digastric muscle and the muscles attached to the styloidprocess. The posterior digastric belly originates in the digas-tric groove, lateral to the occipital groove in which the occip-ital artery courses, and inserts onto the hyoid bone. Themuscles attached to the styloid process, the stylohyoid, stylo-glossus, and stylopharyngeus muscles, extend to the hyoidbone, tongue, and pharyngeal wall, respectively.

Infratemporal fossaThe infratemporal fossa, a route through which some tem-

poral bone lesions can be reached, is a not uncommon site ofinvolvement by lesions that also involve the temporal bone(11). The osseous boundaries of the infratemporal fossa arethe posterolateral maxillary surface anteriorly, the lateralpterygoid plate anteromedially, the mandibular ramus later-ally, and the tympanic part of the temporal bone and thestyloid process posteriorly. The fossa is domed anteriorly bythe infratemporal surface of the greater sphenoid wing, thesite of the foramina ovale and spinosum, and posteriorly bythe squamous part of the temporal bone (Figs. 8.8-8.10). Theinferior, posteromedial, and superolateral aspects are openwithout bony walls.

The structures located in the infratemporal fossa are thepterygoid muscles and venous plexus and the branches of themaxillary artery and mandibular nerve. The lateral pterygoidmuscle crosses the upper part of the infratemporal fossa,originating from the upper and lower heads; the upper headarises from the infratemporal surface of the greater sphenoidwing, and the lower head originates from the lateral ptery-goid plate (Figs. 8.8-8.10). Both heads pass posterolaterally andinsert on the neck of the mandibular condylar process and thearticular disc of the temporomandibular joint. The medial ptery-goid muscle crosses the lower part of the infratemporal fossa

and arises with superficial and deep heads; the superficial headarises from the lateral aspect of the palatine pyramidal processand the maxillary tuberosity and passes superficial to the lowerhead of the lateral pterygoid; and the deep head originates fromthe medial surface of the lateral pterygoid plate and the ptery-goid fossa between the two pterygoid plates and passes deep tothe lower head of the lateral pterygoid. Both heads descendbackward and laterally to attach to the medial surface ofthe mandibular ramus below the mandibular foramen. Thesphenomandibular ligament, located medial to the mandibularcondylar process, descends from the sphenoid spine to attach tothe lingula of the mandibular foramen. The structures located orpassing between the sphenomandibular ligament and the man-dible are the lateral pterygoid and the auriculotemporal nervesuperiorly, and the inferior alveolar nerve, the parotid gland, themaxillary artery and its inferior alveolar branch inferiorly.

The maxillary artery is divided into three segments: man-dibular, pterygoid, and pterygopalatine (Figs. 8.8-8.10). Themandibular segment arises from the external carotid arterynear the posterior border of the condylar process, passesbetween the process and the sphenomandibular ligament,along the inferior border of the lower head of the lateralpterygoid, and gives rise to the deep auricular, anterior tym-panic, middle and accessory meningeal, and the inferior alve-olar arteries. The middle meningeal ascends medial to thelateral pterygoid to enter the foramen spinosum, the accessorymeningeal arises from the maxillary or middle meningeal toenter the foramen ovale, and the inferior alveolar descendsto enter the mandibular foramen. The pterygoid segmentusually courses lateral to, but occasionally medial to, thelower head of the lateral pterygoid and gives rise to the deeptemporal, pterygoid, masseteric, and buccal arteries. Thepterygopalatine segment courses between the two heads ofthe lateral pterygoid and enters the pterygopalatine fossa bypassing through the pterygomaxillary fissure. Its branchingwill be described with the pterygopalatine fossa.

The pterygoid venous plexus is located in the infratemporalfossa and has two parts: a superficial part located betweenthe temporalis and lateral pterygoid; and a deep part situ-ated between the lateral and medial pterygoids anteriorly,and between the lateral pterygoid and the parapharyngealspace posteriorly. The deep part is more prominent and con-nects with the cavernous sinus by emissary veins passingthrough the foramina ovale and spinosum, and occasionallythrough the sphenoidal emissary foramen (foramen of Vesalius).The main drainage of the pterygoid plexus is through the maxillaryvein to the internal jugular vein.

The mandibular nerve enters the infratemporal fossa bypassing through the foramen ovale on the lateral side of theparapharyngeal space, where it gives rise to several smallerbranches, and then divides into a smaller anterior trunk and alarger posterior trunk (Figs. 8.8-8.10). The anterior trunk givesrise to the deep temporal and masseteric nerves, which supplythe temporalis and the masseter, respectively, and the nerveto the lateral pterygoid. The buccal nerve, which conveyssensory fibers, passes anterolaterally between the two headsof the lateral pterygoid, and descends lateral to the lowerhead to reach the buccinator and the buccal mucosa. The

S232 Rhoton


posterior trunk gives off the lingual, inferior alveolar, andauriculotemporal nerves, which descend medial to the lateralpterygoid. The lingual and inferior alveolar nerves, the formercoursing anterior to the latter, pass between the lateral andmedial pterygoids. The auriculotemporal nerve usually splitsto encircle the middle meningeal artery and passes postero-laterally between the mandibular ramus and the sphenoman-dibular ligament. The chorda tympani nerve, which con-tains the taste fibers from the anterior two-thirds of the tongueand the parasympathetic secretomotor fibers to the subman-dibular and sublingual salivary glands, enters the infratem-poral fossa through the petrotympanic fissure, descends me-dial to the auriculotemporal and inferior alveolar nerves, andjoins the lingual nerve. The otic ganglion is situated immedi-ately below the foramen ovale on the medial side of themandibular nerve. The ganglion receives the lesser petrosalnerve, which crosses the floor of the middle fossa anterolat-eral to the greater petrosal nerve to exit through the foramenovale or the more posteriorly situated canaliculus innomina-tus and conveys parasympathetic secretomotor fibers to theparotid gland via the auriculotemporal nerve. The medialpterygoid nerve arises from the medial aspect of the mandib-ular nerve close to the otic ganglion and descends to supplythe medial pterygoid and tensor veli palatini. The nervusspinosus, a meningeal branch, also arises near the otic gan-glion and ascends through the foramen spinosum to innervatethe middle fossa dura.

Parapharyngeal spaceThe parapharyngeal space is located in the lateral pharyn-

geal wall and is shaped like an inverted pyramid, with its baseon the skull base superiorly and its apex at the hyoid boneinferiorly. The parapharyngeal space is subdivided into pre-styloid and poststyloid compartments by the styloid dia-phragm, a fibrous sheet that also constitutes the anterior partof the carotid sheath (Figs. 8.5 and 8.9). The prestyloid part,situated anteriorly between the fascia covering the opposingsurfaces of the medial pterygoid and tensor veli palatini, is athin fat-filled compartment separating the structures in theinfratemporal fossa from the eustachian tube and the tensorand levator veli palatini muscles in the lateral nasopharyngealwall. The upper portion of the prestyloid part is situatedbetween two fascial sheets, which are oriented in a sagittalplane. The lateral sheet arises from the medial surface of themedial pterygoid, passes upward, backward, and medial tothe mandibular nerve and the middle meningeal artery, in-corporating the sphenomandibular ligament posteriorly, andreaching the retromandibular deep lobe of the parotid gland.The medial sheet is formed by the fascia overlying the lateralsurface of the tensor veli palatini and is continuous inferiorlywith the fascia over the superior pharyngeal constrictor andposteriorly with the thick styloid diaphragm, which enve-lopes the stylopharyngeus, styloglossus, and stylohyoid andblends into the carotid sheath. The superior border is locatedwhere the two fascial sheets fuse together and insert in theskull base along a line extending backward from the ptery-goid process lateral to the origin of the tensor veli palatini,

medial to the foramina ovale and spinosum to the sphenoidspine and the posterior margin of the glenoid fossa. Thesharply angled inferior boundary is situated at the junction ofthe posterior digastric belly and the greater hyoid cornu. Thepoststyloid part, which contains the internal carotid artery,internal jugular vein, and the initial extracranial segment ofcranial nerves IX through XII, is separated from the infratem-poral fossa by the posterolateral portion of the prestyloid part.The glossopharyngeal nerve exits the skull through the intra-jugular part of the jugular foramen, anterior to the vagus andaccessory nerves, and passes forward, medial to the styloidprocess in close relationship to the lateral surface of the ca-rotid artery as the artery enters the carotid canal (Fig. 8.9).Care is required to avoid injury to the glossopharyngeal nerveif the artery is to be mobilized at the carotid canal. The vagusnerve leaves the skull through the anteromedial edge of theintrajugular part of the foramen and courses deep withinthe carotid sheath, between the internal carotid artery and thejugular vein. The accessory nerve exits the intrajugular partand runs backward, lateral to the jugular vein and medial tothe styloid process and the posterior belly of the digastricmuscle, to innervate the sternocleidomastoid muscle.

The hypoglossal nerve exits through the hypoglossal canal,deep to the jugular vein and to the nerves emerging from thejugular foramen, and runs downward, between the carotidartery and the jugular vein (Figs. 8.9 and 8.10). It becomessuperficial at the level of the angle of the jaw where it crossesthe internal and external carotid arteries, close to the level ofthe common carotid bifurcation, to innervate the tongue.

Pterygopalatine fossaThe pterygopalatine fossa, which opens laterally into the

medial part of the infratemporal fossa, is bounded posteriorlyby the sphenoid pterygoid process, medially by the palatineperpendicular plate, that bridges the interval between themaxilla and pterygoid process, and opens superiorly throughthe medial part of the inferior orbital fissure into the orbitalapex (Figs. 8.5, 8.9, and 8.10) (11). The fossa contains themaxillary nerve, pterygopalatine ganglion, maxillary artery,and their branches, all embedded in fat tissue. Its lateralboundary, the pterygomaxillary fissure, opens into the infra-temporal fossa and allows passage of the maxillary arteryfrom the infratemporal into the pterygopalatine fossa, wherethe artery gives rise to its terminal branches. The lower part ofthe fossa is funnel-shaped, with its inferior apex openinginto the greater and lesser palatine canals, which transmit thegreater and lesser palatine nerves and vessels, and communi-cate with the oral cavity. The sphenopalatine foramen, locatedin the upper part of the fossa’s medial wall, conveys thesphenopalatine nerve and vessels, and opens into the superiornasal meatus just above the root of the middle nasal concha.The foramen rotundum opens just below the superior orbitalfissure through the superior part of the posterior wall of thefossa. The pterygoid canal opens through the sphenoid ptery-goid process inferomedial to the foramen rotundum and con-veys the vidian nerve carrying autonomic fibers to the ptery-gopalatine ganglion. The maxillary nerve, after entering the

Temporal Bone S233


fossa, gives off ganglionic branches to the pterygopalatineganglion. It then deviates laterally just beneath the inferiororbital fissure, giving rise to, in order, the zygomatic andposterosuperior alveolar nerves outside of the periorbita. Itthen turns medially as the infraorbital nerve, passing throughthe inferior orbital fissure to enter the infraorbital groove,where the anterior and middle superior alveolar nerves arise.Finally, it exits the infraorbital foramen to terminate on thecheek. The pterygopalatine ganglion, located in front of thepterygoid canal and inferomedial to the maxillary nerve, re-ceives communicating rami from the maxillary nerve andgives rise to the greater and lesser palatine nerves from thelower surface of the ganglion, the sphenopalatine nerve andpharyngeal branch from the medial surface, and the orbitalbranch from the superior surface. The vidian nerve is formedby the union of the greater petrosal nerve, which conveysparasympathetic fibers arising from the facial nerve at thelevel of the geniculate ganglion, and the deep petrosal nerve,which conveys sympathetic fibers from the carotid plexus, toreach the lacrimal gland and nasal mucosa. The parasympa-thetic fibers synapse in the pterygopalatine ganglion, whereasthe sympathetic fibers do not. The sympathetic fibers synapsein the superior cervical sympathetic ganglion.

The third or pterygopalatine segment of the maxillary ar-tery enters the pterygopalatine fossa by passing through thepterygomaxillary fissure. This segment courses in an anterior,medial, and superior direction and gives rise to the infraor-bital artery, which passes through the inferior orbital fissureand courses with the infraorbital nerve; the posterosuperioralveolar artery, which descends to pierce the posterolateralwall of the maxilla; the recurrent meningeal branches, whichpass through the foramen rotundum; and the greater andlesser palatine arteries, which descend through the greaterand lesser palatine canals; the vidian artery to the pterygoidcanal; the pharyngeal branch to the palatovaginal canal; andfinally the sphenopalatine artery, which passes through thesphenopalatine foramen to reach the nasal cavity and is con-sidered to be the terminal branch of the maxillary arterybecause of its large diameter. The arterial structures in thepterygopalatine fossa are located anterior to the neuralstructures.

Arterial relationships

The arteries that may be involved in pathological abnor-malities involving the temporal bone include the upper cer-vical and petrous portions of the internal carotid artery, theposteriorly directed branches of the external carotid artery,and the upper portion of the vertebral artery.

Common carotid arteryThe common carotid artery bifurcates into the internal and

external carotid arteries at the level of the upper border of thethyroid cartilage. The internal carotid artery initially ascendsrelatively superficial in the carotid triangle of the neck, butassumes a much deeper position after passing medial to theposterior belly of the digastric (Figs. 8.9 and 8.10). Below thedigastric, it is crossed by the hypoglossal nerve and the ansa

cervicalis, and by the lingual and facial veins. Medial to thedigastric, it is crossed by the stylohyoid muscle and the oc-cipital and posterior auricular arteries. Superior to the digas-tric, the internal carotid artery is separated from the externalcarotid artery by the styloid process and the muscles attachedto it. At the entrance into the carotid canal, the artery isinvolved by a dense sheath of connective tissue and is sepa-rated from the internal jugular vein by the hypoglossal nerveand by the nerves exiting from the jugular foramen.

The internal carotid artery passes, almost straightly up-ward, posterior to the external carotid artery and anterome-dial to the internal jugular vein to reach the carotid canal. Atthe level of the skull base, the internal jugular vein coursesjust posterior to the internal carotid artery, being separatedfrom it by the carotid ridge. Between them, the glossopharyn-geal nerve is located laterally and the vagus, accessory, andhypoglossal nerves medially.

After the internal carotid artery enters the carotid canalwith the carotid sympathetic nerves and surrounding venousplexus, it ascends a short distance (the vertical segment),reaching the area below and slightly behind the cochlea,where it turns anteromedially at a right angle (the site of thelateral bend) and courses horizontally (the horizontal seg-ment) toward the petrous apex (Figs. 8.8-8.10). At the medialedge of the foramen lacerum, it turns sharply upward at thesite of the medial bend to enter the posterior part of thecavernous sinus.

External carotid arteryThe external carotid artery ascends anterior to the internal

carotid artery on the posteromedial margin of the parotidgland and medial to the digastric and stylohyoid muscles.Proximal to its terminal bifurcation into the maxillary and thesuperficial temporal arteries, it gives rise to six branches thatcan be divided into anterior and posterior groups according totheir directions. The latter group is related to the region of thetemporal bone.

The ascending pharyngeal artery, the first branch of theposterior group, often provides the most prominent supply tothe meninges around the jugular foramen (18). It arises eitherat the bifurcation or from the lowest part of the external orinternal carotid arteries. Rarely, it arises from the origin of theoccipital artery. It courses upward between the internal andthe external carotid arteries, giving rise to numerous branchesto neighboring muscles, nerves, and lymph nodes. Its menin-geal branches pass through the foramen lacerum to be dis-tributed to the dura lining the middle fossa and through thejugular foramen or the hypoglossal canal to supply the sur-rounding dura of the posterior cranial fossa. The ascendingpharyngeal artery also gives rise to the inferior tympanicartery, which reaches the tympanic cavity by way of thetympanic canaliculus along with the tympanic branch of theglossopharyngeal nerve.

The occipital artery, the second and largest branch of theposterior group, arises from the posterior surface of the ex-ternal carotid artery and courses obliquely upward betweenthe posterior belly of the digastric muscle and the internal

S234 Rhoton


jugular vein, and then medial to the mastoid process andeither superficial or deep to the longissimus capitis muscle(Fig. 8.5). It courses deep to the latter muscle if it courses in theoccipital groove of the mastoid bone, which is located medialto the digastric groove. After passing the longissimus capitismuscle, the occipital artery courses deep to the splenius capi-tis muscle, finally reaching a subcutaneous location by pierc-ing the fascia between the attachment of the sternocleidomas-toid and the trapezius muscles to the superior nuchal line. Theoccipital artery gives rise to several muscular and meningealbranches, anastomoses with other branches of the externalcarotid including the ascending pharyngeal and also withbranches of the vertebral artery. Its meningeal branches,which enter the posterior fossa through the jugular foramenor the condylar canal, may make a significant contribution totumors of the jugular foramen.

The posterior auricular artery, the last branch in the poste-rior group, arises above the posterior belly of the digastricmuscle and travels between the parotid gland and the styloidprocess. At the anterior margin of the mastoid process, itdivides into auricular and occipital branches, which are dis-tributed to the postauricular and the occipital regions, respec-tively. The stylomastoid branch, which arises below the stylo-mastoid foramen, enters the stylomastoid foramen to supplythe facial nerve. Its loss can lead to a facial palsy, even thoughit anastomoses with the petrosal branch of the middle men-ingeal artery. The posterior auricular branch may share acommon trunk with the occipital artery, or sometimes it isabsent, in which case, the occipital artery gives rise to thestylomastoid artery. Members of the anterior group, whoseorigins may be visualized in exposing lesions in the region,include the superior thyroid, lingual, and facial arteries.

The superficial temporal artery arises from the externalcarotid artery in the substance of the parotid gland behind theneck of the mandible where it is crossed by the temporal andzygomatic branches of the facial nerve (Fig. 8.5). It ascendsover the posterior root of the zygoma and divides into ante-rior and posterior branches that run with the superficial tem-poral vein and the auriculotemporal nerve over the superficialtemporalis fascia.

Vertebral arteryThe vertebral artery and its meningeal, posterior spinal,

and posteroinferior cerebellar branches, which may be ex-posed in approaches directed through the temporal bone, aredetailed in the chapter on the foramen magnum (4, 20, 24).

Venous relationships

The venous drainage of the structures of the skull base isthrough the internal jugular veins, the sinuses in the duramater, and a series of emissary veins communicating theintra- and extracranial compartments (25). The superior petro-sal sinus sits on the petrous ridge and connects the cavernousand transverse sinuses. It receives tributaries from the inferiorsurface of the temporal lobe and from the petrosal veins thatdrain the cerebellum and brainstem. The inferior petrosalsinus courses along the petro-occipital fissure and drains the

clival area. It consists of one or more channels that, at its lowerend, course rostral or caudal to or between the nerves passingthrough the jugular foramen. It enters the medial wall of thejugular bulb just anterior to where the cranial nerves descendin the anteromedial wall of the jugular bulb (18). It joins thecavernous sinus at its upper margin. The transverse sinusbegins at the level of the internal occipital protuberance andpasses laterally and forward to the posterolateral part of thetemporal bone where it joins the superior petrosal sinus andcontinues as the sigmoid sinus. It receives drainage from thetentorial surface of the cerebellum through the tentorial si-nuses and from the temporal lobe through the vein of Labbe.The basilar venous plexus consists of multiple interconnectingchannels situated between the layers of dura mater on theclivus. It forms the largest communication between the pairedcavernous sinus and communicates through the inferiorpetrosal sinuses with the sinuses in the region of the foramenmagnum (10).

SURGICAL APPROACHES

The suboccipital retrosigmoid approach, the traditionalneurosurgical route to intradural pathologies arising in theregion of the cerebellopontine angle, lower clivus, and fora-men magnum, is reviewed in the chapter on the cerebellopon-tine angle. The approaches reviewed here are those directedthrough the temporal bone.

Middle fossa approach

This section focuses on the middle fossa approach to theinternal acoustic meatus rather than on the more extensiveapproaches directed through the petrous apex to the petroclivalregion or the more extended approaches directed through thetemporal bone lateral to the internal acoustic meatus. The middlefossa approach to the internal acoustic meatus is usually selectedfor small tumors that are located predominantly within theinternal acoustic meatus in which there is an opportunity topreserve hearing. With this approach, the meatus is approachedfrom above, through a temporal craniotomy located above theear and zygoma (Figs. 8.7 and 8.11) (2). The dura under thetemporal lobe is elevated from the floor of the middle cranialfossa until the arcuate eminence and the greater petrosal nerveare identified. The distance from the inner table of the skull to thefacial hiatus, through which the greater petrosal nerve passes,ranges from 1.3 to 2.3 cm (average, 1.7 cm) (42). When separatingthe dura from the floor of the middle fossa, one should remem-ber that bone may be absent over all or part of the geniculateganglion. In our previous study of 100 temporal bones, all or partof the geniculate ganglion and the genu of the facial nerve werefound to be exposed in the floor of the middle fossa in 15 bones(15%) (31). In 15 other specimens, the geniculate ganglion wascompletely covered, but no bone extended over the greaterpetrosal nerve. The greatest length of greater petrosal nervecovered by bone was 6.0 mm. More than 50% of the specimenshad less than 2.5 mm of greater petrosal nerve covered. It also isimportant to remember that the petrous segment of the carotidartery may be exposed without a covering of bone in the floor ofthe middle fossa deep to the greater petrosal nerve (17) In a

Temporal Bone S235


FIGURE 8.11. Middle fossa approach to the internal acoustic meatus. A, the vertical line shows the site of the scalp incision andthe stippled area outlines the bone flap bordering the middle fossa floor. B, the dura has been elevated to expose the middle men-ingeal artery, the greater petrosal nerve, and the arcuate eminence. C, bone has been removed to expose the junction of thegreater petrosal nerve and the geniculate ganglion. A portion of the upper wall of the internal meatus has been removed. Theupper surface of the arcuate eminence has been drilled to expose the superior semicircular canal. In the middle fossa approach, foran acoustic neuroma, the cochlea and semicircular canal are not opened, as seen in this dissection illustrating some of the impor-tant structures that are to be avoided in opening the meatus. D, enlarged view. The cochlea, located below the middle fossa floorin the angle between the facial and greater petrosal nerves, has been opened in the area anteromedial to the meatal fundus. Theroof of the meatus has been opened to expose the superior vestibular nerve, which innervates the ampullae of the superior andlateral canals and the meatal segment of the facial nerve. E, the vestibule and semicircular canals are located posterolateral and thecochlea is located anteromedial to the meatal fundus. The tensor tympani is layered along the anterior edge and the greater petro-sal nerve above the petrous carotid. F, enlarged view. The vertical crest (Bill’s bar) separates the facial and superior vestibularnerves at the meatal fundus. The superior and inferior vestibular nerves are located posteriorly and the facial and cochlear nervesanteriorly in the meatus, with the cochlear nerve passing below the facial nerve to enter the modiolus. The labyrinthine segment ofthe facial nerve courses superolateral to the cochlea. A., artery; Ac., acoustic; Arc., arcuate; Car., carotid; CN, cranial nerve; Coch.,cochlear; Emin., eminence; Gang., ganglion; Genic., geniculate; Gr., greater; Inf., inferior; Int., internal; Laby., labyrinthine; M.,muscle; Meat., meatal; Men., meningeal; Mid., middle; N., nerve; Pet., petrosal, petrous; Post., posterior; Seg., segment; Sup., supe-rior; Tens., tensor; Tymp., tympani; Vert., vertebral; Vest., vestibular.

S236 Rhoton


previous study, we found that a 7-mm length of petrous carotidartery may be exposed without a bony covering in the areabelow where the greater petrosal nerve passes below the lateralmargin of the trigeminal ganglion to reach the vidian canal at theanterior margin of the anterior margin of the foramen lacerum(30, 31). The foramen spinosum and middle meningeal arteryand the foramen ovale and third trigeminal division are situatedat the anterior margin of the extradural exposure. The extraduralexposure can usually be completed without obliterating the mid-dle meningeal artery at the foramen spinosum.

Two different methods are used for exposing the internalacoustic meatus. One is to remove bone over the greaterpetrosal nerve and to follow it to the geniculate ganglion andthe genu of the facial nerve. From here, the labyrinthineportion of the facial nerve is followed to the lateral end of theinternal auditory canal, after which the canal is unroofed. Theother method is begun by drilling just in front of the petrousridge in the area medial to the arcuate eminence. The anglebetween the long axis of the superior semicircular canal or thegreater petrosal nerve and the long axis of the internal acous-

FIGURE 8.12. A–D. Anterior petrosectomy and extendedmiddle fossa approach. A, the site of the bone flap is thesame as shown in Figure 8.11A. The dura has been elevatedfrom the floor of the middle fossa. Bone has been removedto expose the geniculate ganglion, the dura lining theinternal acoustic meatus, the tensor tympani, some of thepetrous carotid, and the superior semicircular canal. B, thebone of the petrous apex between the trigeminal nerve andthe internal acoustic meatus has been removed to exposethe side of the clivus. C, the exposure under the trigeminal nerve extends to the edge of the inferior petrosal sinus. D, theposterior fossa dura has been opened to expose the prepontine cistern, basilar artery, and abducens nerve. A., artery; Ac.,acoustic; A.I.C.A., anteroinferior cerebellar artery; Bas., basilar; Car., carotid; Cav., cavernous; Chor., chorda; CN, cranialnerve; Ext., external; Gang., ganglion; Gen., geniculate; Genic., geniculate; Inf., inferior; Int., internal; Laby., labyrinthine;Lat., lateral; M., muscle; Mast., mastoid; Men., meningeal; Mid., middle; N., nerve; P.C.A., posterior cerebral artery; Pet.,petrosal, petrous; P.I.C.A., posteroinferior cerebellar artery; Post., posterior; S.C.A., superior cerebellar artery; Seg., segment;Sup., superior; Tens., tensor; Tymp., tympani; Tent., tentorial; Trig., trigeminal; Tymp., tympani, tympanic.

Temporal Bone S237


tic meatus is helpful in selecting the site for drilling. The longaxis of the central part of the internal acoustic meatus islocated an average of 61 degrees behind the long axis of thegreater petrosal nerve and an average of 37 degrees medial tothe long axis of the arcuate eminence and superior semicircu-lar canal. The drilling is directed anterolateral to the meatalfundus where the vertical crest is identified.

The lateral part of the bone removal near the meatal fundusis limited posteriorly by the superior semicircular canal,which is located a few millimeters behind and oriented par-allel to the labyrinthine segment of the facial nerve (Figs. 8.7and 8.11). The anteromedial edge of the exposure is limited bythe cochlea, which sits only a few millimeters anterior to thesite of bone removal, in the angle between the labyrinthineportion of the facial nerve and the greater petrosal nerve. Thecochlea and the semicircular canals should be avoided in this

approach if hearing is to be preserved. The vertical crest,which is identified at the upper edge of the meatal fundus,provides a valuable landmark for identifying the facial nerve.In the final stage of bone removal, the upper wall of theinternal auditory canal is removed to expose the dura liningthe entire superior surface of the internal auditory canalfrom the vertical crest to the porus. The dura is opened toexpose the pathology.

The extended middle fossa approach used for the removalof larger acoustic neuromas includes wider opening of theposterior part of the petrous pyramid (21, 28, 42, 43). Thisapproach combines different degrees of resection of the bonylabyrinth with the subtemporal transtentorial routes (Fig.8.12). Extending the resection of the petrous bone posteriorlyover the mastoid and the bony labyrinth exposes the wholeintrapetrous course of the facial nerve, and provides access to

FIGURE 8.12. E–H. Anterior petrosectomy and extended middle fossa approach. E, additional bone has been removedaround the internal acoustic meatus and the dura opened to expose the facial and vestibulocochlear nerves. F, the exposurehas been extended lateral to the internal acoustic meatus. The tegmen has been opened to expose the head of the incus inthe epitympanic area. The osseous capsule of the labyrinth has been opened to expose the semicircular canals. The presig-moid dura behind the labyrinth has been exposed and opened. G, a translabyrinthine approach directed through the middlefossa has been completed by removing the semicircular canals and vestibule. The dura has been opened to give an exposurethrough the middle fossa similar to that seen with the presigmoid approach. The labyrinthine, tympanic, and mastoid seg-ments of the facial nerve have been exposed. H, this extended middle fossa exposure extends from the lateral wall of the cav-ernous sinus, across the trigeminal nerve to the area lateral to the internal acoustic meatus, and provides wide access to theanterior part of the posterior fossa.

S238 Rhoton


FIGURE 8.13. A–F. Subtemporal exposure of the right middle, infratemporal, and posterior fossae. A, the insert shows the side of thescalp incision. A frontotemporal craniotomy has been completed and the dura has been elevated from the middle fossa floor and lateralwall of the cavernous sinus. B, enlarged view. The bony roof over the geniculate ganglion and internal meatus has been removed and thedura lining the meatus opened to expose the facial and superior vestibular nerves. C, additional middle fossa floor has been removed toexpose the petrous carotid, the cochlea in the angle between the greater petrosal nerve and pregeniculate part of the facial nerve, thesemicircular canals and tympanic cavity. The tensor tympani muscle and eustachian tube are exposed in front of the petrous carotidartery. D, the bone between the superior and posterior canals has been removed to expose the vestibule with which both ends of thesemicircular canals communicate. The vestibule contains the utricle and saccule and communicates below the fundus of the meatus withthe cochlea. The meatal segment of the facial nerve courses in the internal acoustic meatus, the labyrinthine segment between the semi-circular canals and the cochlea, the tympanic segment between the anterior margin of the lateral canal and the oval window on themedial side of the tympanic cavity, and the mastoid segment descends to exit the stylomastoid foramen. E, the petrous apex, medial tothe cochlea and extending under the trigeminal nerve, has been removed to expose the lateral edge of the clivus and the posterior fossadura. F, the medial tentorial edge has been divided behind the petrous ridge to expose the oculomotor, trochlear, and trigeminal nervesand the basilar artery. A., artery; A.I.C.A., anteroinferior cerebellar artery; Alv., alveolar; Ant., anterior; Bas., basilar; Car., carotid; Chor.,chorda, choroidal; CN, cranial nerve; Comm., communicating; Eust., eustachian; Gang., ganglion; Gen., geniculate; Genic., geniculate;Gr., greater; Inf., inferior; Int., internal; Jug., jugular; Laby., labyrinthine; Lat., lateral; M., muscle; Mandib., mandibular; Mast., mastoid;Max., maxillary; Meat., meatal; Men., meningeal; Mid., middle; N., nerve; P.C.A., posterior cerebral artery; Pet., petrosal, petrous; Post.,posterior; S.C.A., superior cerebellar artery; Seg., segment; Sup., superior; Temp., temporal; Tens., tensor; Trig., trigeminal; Tymp., tym-pani, tympanic; V., vein; Vert., vertebral; Vest., vestibular.

Temporal Bone S239


FIGURE 8.13. G–L. Subtemporal exposure of the right middle, infratemporal, and posterior fossae. G, the dural opening has beenextended downward to expose the lateral edge of the clivus and the inferior petrosal sinus coursing along the petroclival fissure.The abducens nerve and the AICA are in the lower margin of the exposure. H, an osteotomy of the zygomatic arch and the floorof the middle fossa surrounding the mandibular fossa has been completed to aid in exposing the infratemporal fossa. I, the mandib-ular fossa and floor of the middle fossa, extending medially to the level of the foramen ovale, have been removed. Branches of themandibular nerve and maxillary artery are exposed in the infratemporal fossa. The greater petrosal nerve joins the deep petrosalnerve from the carotid sympathetic plexus to form the vidian nerve, which passes forward in the vidian canal to reach the pterygo-palatine fossa. J, the upper portion of the cervical carotid is exposed medial to the jugular foramen. The petrous carotid crossesbehind the eustachian tube and tensor tympani. K, the eustachian tube and tensor tympani have been resected, the petrous carotidreflected forward out of the carotid canal, the petrous apex removed, and the posterior fossa dura opened to expose the vertebralartery and the AICA. L, enlarged view. The right vertebral artery has been displaced forward to expose the left vertebral artery.The AICA passes toward the nerves entering the internal acoustic meatus.

S240 Rhoton


the cerebellopontine angle by a combination of subtemporal,translabyrinthine, and presigmoid routes, all directed throughthe posterior part of the floor of the middle fossa.

Subtemporal anterior transpetrosal approach

This approach is made through a temporal craniotomy thatextends down to the floor of the middle fossa (Figs. 8.12 and

8.13) (19). The dura is carefully elevated from the floor of themiddle fossa to expose the middle meningeal artery, whichmay be obliterated and divided at the foramen spinosum.Further elevation of the dura toward the petrous ridge willexpose the arcuate eminence and greater petrosal nerve pos-teriorly. The cochlea, which is to be preserved, and the ante-rior wall of the internal auditory canal constitute the lateral

FIGURE 8.14. A–D. Presigmoidapproach. A, the insert shows thetemporo-occipital craniotomy andthe mastoid exposure. Themastoidectomy has beencompleted and the dense corticalbone around the labyrinth hasbeen exposed. The tympanicsegment of the facial nerve andthe lateral canal are situated deepto the spine of Henley.Trautman’s triangle, the patch ofdura in front of the sigmoid sinus,faces the cerebellopontine angle.B, the presigmoid dura has beenopened and the superior petrosalsinus and tentorium divided,taking care to preserve the vein ofLabbe that joins the transversesinus, and the trochlear nerve thatenters the anterior edge of thetentorium. The abducens andfacial nerves are exposed medialto the vestibulocochlear nerve.The posteroinferior cerebellarartery courses in the lower marginof the exposure with theglossopharyngeal and vagusnerves. The SCA passes below theoculomotor and trochlear nervesand above the trigeminal nerve.C, the semicircular canals havebeen opened. The superior canalis located under the middle fossa’sarcuate eminence and theposterior canal is locatedimmediately lateral to theposterior wall of the internalacoustic meatus. D, labyrinthineexposure in another specimen.The tympanic segment of thefacial nerve courses below the lateral canal and turns downward as the mastoid segment where it gives origin to thechorda tympani, seen ascending along the inner surface of the tympanic membrane and neck of the malleus. The headof the malleus and incus are located in the epitympanic area above the level of the tympanic membrane. The mastoidantrum communicates through the aditus with the epitympanic area and tympanic cavity. A., artery; Ac., acoustic;A.I.C.A., anteroinferior cerebellar artery; Bas., basilar; Br., branch; Chor., chorda; Cist., cisternal; CN, cranial nerve;Coch., cochlear; Gang., ganglion; Genic., geniculate; Inf., inferior; Int., internal; Jug., jugular; Laby., labyrinthine; Lat.,lateral; Marg., margin; Mast., mastoid; Meat., meatal; Memb., membrane; N., nerve; Pet., petrosal; P.I.C.A.,posteroinferior cerebellar artery; Post., posterior; S.C.A., superior cerebellar artery; Seg., segment; Sp., spine; Sup.,superior; Tymp., tympani, tympanic; V., vein; Vert., vertebral; Vest., vestibular.

Temporal Bone S241


limit of the exposure through the petrous apex. The bone layerover the superior wall of the internal auditory canal, whichaverages 5 mm (range, 3–7 mm) in thickness, can be removedwith a drill to improve the exposure (44). The petrous carotidforms the anterior limit of the exposure. The limit above themedial part of the bone resection is the trigeminal nerve inMeckel’s cave. Drilling is directed behind the petrous carotid,through the petrous apex medial to the cochlea and under thetrigeminal nerve. The petrous apex is removed and the boneremoval is extended to the lateral side of the clivus, exposing

the inferior petrosal sinus at the lateral edge of the clivus. Care isrequired to prevent damage to the abducens nerve as it passesthrough Dorello’s canal located at the upper edge of the petro-clival fissure. The width of the bone resection from the trigemi-nal impression to the posterior wall of the internal auditory canalaverages 13 mm (range, 9–14 mm) (44). The depth of the expo-sure, from the trigeminal ganglion to the petroclival fissure,averages 13 mm (range, 9–17 mm). The cochlea lies below thefloor of the middle fossa near the apex of the angle formed bythe greater petrosal nerve anteriorly and the internal acoustic

FIGURE 8.14. E–H. Presigmoidapproach. E, thelabyrinthectomy has beencompleted to expose the internalacoustic meatus. F, the duralining the meatus has beenopened and the facial nerve hasbeen transposed posteriorly. Thefacial segments are the cisternalsegment located in the cisternmedial to the meatal porus, themeatal segment that extendslaterally from the porus to themeatal fundus, the labyrinthinesegment that is located betweenthe fundus and the geniculateganglion, the tympanic segmentthat arises at the ganglion andthe sharp turn, the genu, andpasses between the lateralsemicircular canal and the ovalwindow, and the mastoidsegment that descends to exitthe stylomastoid foramen. Thelabyrinthine segment coursesbetween the semicircular canalsand vestibule on itsposterolateral side and thecochlea on its anteromedialmargin. The superior andinferior vestibular nerves havelost their end organs with thedrilling of the semicircularcanals and vestibule. Thecochlear nerve passes laterallyto enter the cochlea, which isstill preserved in the boneanteromedial to the fundus ofthe meatus. G, the cochlearnerve has been divided andreflected and bone removed toexpose the cochlea. H, thetranscochlear exposure,completed by removing the

cochlea and surrounding petrous apex, provides access to the front of the brainstem and vertebrobasilar junction, but atthe cost of loss of hearing due to the labyrinthectomy and almost certain temporary or permanent facial weaknessassociated with the posterior transposition of the facial nerve.

S242 Rhoton


meatus posteriorly. The cochlea is to be avoided if hearing is tobe preserved.

After the bone removal is completed, the superior petrosalsinus is obliterated and divided in the area just lateral to thetrigeminal nerve, and the dural incision is extended across thetentorium. The dural leaflets of the tentorium are retractedwith sutures and the dural incision is carried downward to

the lower margin of the opening through the petrous apex.The approach is then directed between the lower margin ofthe trigeminal nerve above, and the internal acoustic meatusinferiorly and laterally (20).

The exposure is small, as described above, and may requiresignificant temporal lobe retraction, especially if the goal is toreach the lower aspect of the brainstem. To reach the anterior

FIGURE 8.15. A–D. Com-parison of the retrosig-moid approach and the mini-mal mastoidectomy,retrolabyrinthine, translabyrin-thine, and transcochlearapproach modifications of thepresigmoid approach. A, ret-rosigmoid approach. The leftcerebellum has been elevated toexpose the cranial nerves Vthrough XI in the cerebel-lopontine angle. The illustra-tions from each step are to becompared with the viewsfrom the other modificationsof the approach. B, the facialand vestibulocochlear nervesand the flocculus have beenretracted to expose the sideof the basilar artery. C, forthe minimal mastoidectomy,only enough bone is removedin front of the sigmoid sinusto open the presigmoid duraand divide the superior petro-sal sinus and tentorium. D,the presigmoid dura has beenopened and the sigmoid sinushas been retracted posteri-orly. The view is approxi-mately the same as that seenwith the retrosigmoid expo-sure. The retrosigmoid ap-proach provides a better viewof the nerves entering thejugular foramen. A., artery;A.I.C.A., anteroinferior cere-bellar artery; Bas., basilar;Cist., cisternal; CN, cranialnerve; Coch., cochlear;Flocc., flocculus; Inf., infe-rior; Laby., labyrinthine; Lat.,lateral; Mast., mastoid; Meat., meatal; N., nerve; Pet., petrosal;P.I.C.A., posteroinferior cerebellar artery; Post., posterior; Presig.,presigmoid; S.C.A., superior cerebellar artery; Seg., segment; Sig., sigmoid;Suboccip., suboccipital; Sup., superior; Tymp., tympanic; V., vein; Vest.,vestibular.

Temporal Bone S243


aspect of the pons, the view must be directed from lateral tomedial above the internal auditory canal. The angles of viewthrough the area of the petrousectomy can be increased if thecranium is approached at a higher level through a frontotem-poral craniotomy combined with zygomatic arch resection.

Translabyrinthine approachIn the translabyrinthine approach, the internal acoustic me-

atus and cerebellopontine angle are approached through amastoidectomy and labyrinthectomy (Fig. 8.6) (16, 29, 38)There are two goals of bone removal in this approach. Thefirst is to expose the dura of Trautman’s triangle on theposterior surface of the temporal bone facing the cerebel-lopontine angle. The second is to remove enough bone to be ableto identify the nerves lateral to the tumor as they course through

the internal auditory canal and by the transverse and verticalcrests. The approach may also be combined with a retrosigmoidor a supra- and infratentorial presigmoid approach.

A retroauricular incision starts above the pinna and extendsinferiorly to the mastoid tip (3). A flap of periosteum and softtissues overlying the mastoid and retromastoid areas is ele-vated. The cortical bone over the mastoid is drilled away andthe mastoid air cells are removed, exposing the mastoid an-trum, the cortical bone around the labyrinth, and the digastricridge leading anteriorly to the mastoid segment of the facialnerve as it exits the stylomastoid foramen and the sinoduralangle. Drilling is continued to expose the semicircular canalsand to skeletonize the sigmoid sinus, middle fossa dura,mastoid segment of the facial nerve, and the upper surface ofthe jugular bulb, leaving only a thin shell of bone over these

FIGURE 8.15. E–H. Comparison of theretrosigmoid approach and the minimalmastoidectomy, retrolabyrinthine,translabyrinthine, and transcochlearapproach modifications of thepresigmoid approach. E, the bonycapsule around the semicircular canalsand the facial nerve have been exposedfor the retrolabyrinthine variant of thepresigmoid approach. F, the exposure

with the retrolabyrinthineversion does not differsignificantly from thatachieved with the minimalmastoidectomy. G, thesemicircular canals andvestibule have been removedand the dura lining theinternal acoustic meatus hasbeen opened to complete thetranslabyrinthine exposure.This yields an exposure of theinternal acoustic meatus butprovides only minimalimprovement in the exposureof the structures medial to theporus of the meatus. H, thenerves have been separatedbeginning laterally at thefundus of the meatus andextending the cleavage planemedially toward the brainstem.The superior vestibular nerveis behind the facial nerve andthe inferior vestibular nerve isbehind the cochlear nerve.

S244 Rhoton


structures. The lateral semicircular canal is the most laterallyprojecting canal and is the first one encountered by this ap-proach. It provides a valuable landmark in identifying thetympanic segment of the facial nerve and the other canals. Thenerve is found below the lateral canal. The retrofacial air cellsare removed and the dome of the jugular bulb is identifiedinferiorly. In removing bone behind the internal acoustic me-atus, it is important to remember that the jugular bulb maybulge upward behind the posterior semicircular canal or in-ternal auditory meatus. The vestibular aqueduct and the en-dolymphatic sac may be opened and removed during thebone removal between the meatus and the jugular bulb. Thecochlear canaliculus will be seen deep to the vestibular aque-duct as bone is removed in the area between the meatus andthe jugular bulb. The lower end of the cochlear canaliculus issituated just above the area where the glossopharyngeal nerveenters the medial half of the jugular foramen. The labyrinthec-tomy portion of the procedure involves removing the semi-circular canals and the vestibule to expose the dura lining theinternal auditory canal. The lateral and posterior semicircularcanals are drilled away. As the bone removal proceeds medi-ally, the ampullae of the lateral and superior semicircularcanals are exposed. At this point some bleeding can occur asthe subarcuate artery is encountered in the bone near thecenter of the superior semicircular canal. The vestibule is anoval-shaped cavity located immediately lateral to the internalacoustic meatus, which forms the communication between thesemicircular canals and the cochlea. Bone is removed medialand posterior to the vestibule, completely exposing it anteriorand inferior to the facial nerve. Care is required to avoidinjury to the facial nerve as it courses below the lateral canal

and the ampullae of the posterior canal and around the su-perolateral margin of the vestibule.

The internal auditory canal is located medial and anterior tothe tympanic segment of the facial nerve. The dura lining theinternal canal is exposed by drilling away the semicircularcanals and vestibule and the bone around the superior, pos-terior, and inferior margins of the internal canal. Further boneremoval at the lateral end of the meatus exposes the trans-verse and vertical crests (Fig. 8.2). The intrameatal portion ofthe facial nerve is separated from the superior vestibularnerve at the lateral end of the canal by the vertical crest, alsocalled Bill’s bar, that can be used to positively identify thefacial nerve (13, 16). The initial part of labyrinthine segment ofthe facial nerve, which lies just in front of the vertical crest, isexposed at the meatal fundus. After identifying the facialnerve, the dura lining the meatus is opened. The dural inci-sion in Trautman’s triangle is V-shaped with the apex of the“V” extending to the incision along the meatal dura. One limbof the “V” extends below the superior petrosal sinus and theother limb extends above the jugular bulb. The dural flap isthen reflected posteriorly to expose the structures in the me-atus and the cerebellopontine angle. The subarcuate artery, orthe AICA, may be encountered in the dura of Trautman’striangle. Usually, the subarcuate artery arises from the AICAand passes through the dura on the upper posterior wall ofthe meatus as a fine stem. Occasionally, however, the subar-cuate artery, along with its origin from the AICA, may beincorporated into the dura on the posterior face of the tem-poral bone. The approach may include transection of theexternal canal and obliteration of the middle ear with packingof the eustachian tube at closure.

FIGURE 8.15. I and J. Compari-son of the retrosigmoidapproach and the minimal mas-toidectomy, retrolabyrinthine,translabyrinthine, and transco-chlear approach modifications ofthe presigmoid approach. I, thelabyrinthine, tympanic, and mas-toid segments of the facial nervehave been exposed in prepara-tion for the posterior transposi-tion of the nerve needed tocomplete the transcochlearexposure. J, the facial nerve hasbeen transposed and the cochleaand petrous apex removed tocomplete the transcochlearexposure of the anterior aspectof the brainstem and the basilarartery.

Temporal Bone S245


FIGURE 8.16. A–F. Comparison of the retrosigmoid and the various modifications of the presigmoid exposure. The modifica-tions of the presigmoid approach include the minimal mastoidectomy, retrolabyrinthine, partial labyrinthine, translabyrin-thine, modified transcochlear, and the full transcochlear approach with facial nerve transposition. A, the scalp incision(insert) is positioned for a supra- and infratentorial exposure through a temporo-occipital craniotomy. A temporo-occipitalcraniotomy has been completed and the dura opened to expose the temporal lobe and the retrosigmoid area. The transverseand sigmoid sinuses have been preserved. The cerebellum has been retracted to expose the nerves in the cerebellopontineangle. B, enlarged view of the retrosigmoid exposure to compare with the exposure obtained with the various modification ofthe presigmoid approach. C, in the retrosigmoid exposure the vestibulocochlear nerve has been elevated and the glossopha-ryngeal nerve depressed to expose the basilar artery at the origin of the AICA. D, subtemporal exposure. The temporal lobehas been elevated to expose the optic tract and oculomotor nerve and the PCA, internal carotid, and anterior choroidal arter-ies. E, the tentorium has been opened while preserving the trochlear nerve. The SCA courses below and the PCA above the

S246 Rhoton


Transcochlear approach

The transcochlear approach is primarily an anteromedialextension of the translabyrinthine approach (Fig. 8.6) (3, 15,16). It usually includes division and closure of the externalcanal, resection of at least the posterior part of the osseousexternal canal, and the tympanic membrane and ossicles, andobliteration of the eustachian tube. After exposing the duralining the internal auditory canal, as described for the trans-labyrinthine approach, the incus is removed and the facialnerve is exposed from the geniculate ganglion to the stylo-mastoid foramen. The greater superficial petrosal nerve istransected and the facial nerve is transposed posteriorly. Inthe final stage, the bone removal is carried through the facialcanal, after nerve transposition, and the cochlea and adjacentpart of the petrous apex are drilled away (Fig. 8.6).

Medially, the bone removal extends to the edge of theclivus, exposing the inferior petrosal sinus from the jugularbulb below to the superior petrosal sinus above. The ascend-ing portion of the petrous carotid is exposed at the anteriorlimit of the dissection. The bone removal, which now extendsto the lateral edge of the clivus, could easily be carried medi-ally into the clivus. Extending the dural opening in this areapermits visualization of the abducent nerve medial to theinternal acoustic meatus, the lower margin of the trigeminalnerve, the nerves entering the jugular foramen, a segment ofthe basilar artery, and the origin and initial segment of theAICA.

An alternative to transposing the facial nerve is to completean extensive bone removal in the hypotympanic and retrofa-cial areas extending forward to the carotid canal, thus skele-tonizing the mastoid segment of the facial nerve and leavingit suspended in a shell of bone, as described by Gantz andFisch (7). In this approach, the external auditory canal isclosed as a blind sac and the tympanic membrane, incus, andbody of the malleus are removed (7). A mastoidectomy isperformed, including the removal of the retrofacial, retrolaby-rinthine, and supralabyrinthine compartments. The facialnerve is identified at its tympanic segment and at the stylo-mastoid foramen. The inferior part of the tympanic bone isremoved to expose the infralabyrinthine compartment, thejugular bulb, and the intrapetrous carotid artery. The retrofa-cial dissection is carried medially and superiorly, removingthe semicircular canals and vestibule. The dissection of theposterior fossa dura is carried inferiorly around the internalauditory canal and under the facial canal. The cochlea isdrilled away by working inferior and anterior to the facial

canal. The facial canal is then left as a bridge over the opera-tive field and the dura is exposed between the carotid arteryand the jugular bulb.

Combined supra- and infratentorialpresigmoid approach

The presigmoid approach combines the supra- and infrat-entorial craniotomy centered on the mastoid and varyingdegrees of mastoid and labyrinthine resection (Fig. 8.14).The minimal degree of mastoid resection, which we refer to asa minimal mastoidectomy, exposes only enough of the presig-moid dura to open the dura in front of the sigmoid sinus forexposure of the cerebellopontine angle (Figs. 8.15 and 8.16).The next more extensive degree of mastoid resection, theretrolabyrinthine modification, is a more complete mastoid-ectomy exposing the bony capsule of the semicircular canalsand skeletonizing at least a portion of the facial nerve. In thepartial labyrinthectomy, one or two of the semicircular canals,commonly the superior and/or posterior canals, are resectedwith preservation of the lateral canal. Removal of these canalsmay, but not always, be associated with the loss of hearing(37). The posterior canal may be removed to increase access tothe posterior fossa, and removing the superior canal alonegives a more direct access to the petrous apex along themiddle fossa. The next more extensive modification is thetranslabyrinthine approach, in which the semicircular canalsand vestibule are resected uniformly, resulting in the loss ofhearing. The translabyrinthine approach provides excellentaccess to the internal auditory canal. The next more extensivemodification is the transcochlear approach, in which the co-chlea located anteromedial to the fundus of the meatus isremoved, thus providing access to the medial part of thepetrous apex and the side of the clivus. Another modification,which we call the extended translabyrinthine approach, and issimilar to the transcochlear approach, involves drilling boneboth anterior and posterior to the facial nerve, leaving thefacial nerve skeletonized in a column of bone and workingboth anterior and posterior to the facial nerve to remove thecochlea and access the side of the clivus. Gaining access fordrilling the cochlea anterior to the facial nerve commonlyrequires that at least part of the posterior part of the externalcanal be removed, that the tympanic cavity be obliterated, andthat the internal carotid artery be exposed below thepromontory.

In evaluating these approaches in our laboratory, we havefound that the minimal mastoidectomy gives approximately

Š

oculomotor and trochlear nerves. F, minimal mastoidectomy modification of the presigmoid approach. The minimal mastoid-ectomy approach is completed by removing only enough bone in the front of the sigmoid sinus so that the presigmoid duracan be opened to expose the posterior cranial fossa. The bony capsule of the labyrinth is not exposed in the minimal mastoid-ectomy as it is in the retrolabyrinthine approach. The exposure shown with the minimal mastoidectomy in this figure is to becompared with the retrosigmoid exposure shown in B. A., artery; Ac., acoustic; A.I.C.A., anteroinferior cerebellar artery;Ant., anterior; Bas., basilar; Car., carotid; Chor., choroidal; CN, cranial nerve; Comm., communicating; Inf., inferior; Int.,internal; Lat., lateral; Mast., mastoid; P.C.A., posterior cerebral artery; Ped., peduncle; Pet., petrosal; P.I.C.A., posteroinferiorcerebellar artery; Post., posterior; S.C.A., superior cerebellar artery; Seg., segment; Sig., sigmoid; Sup., superior; Temp., tem-poral; Tent., tentorial; Tr., trunk; Trans., transverse; V., vein; Vert., vertebral.

Temporal Bone S247


S248 Rhoton


the same exposure as the retrolabyrinthine approach, but isdone at reduced risk since the semicircular canals and facialnerve are not skeletonized (Figs. 8.14 and 8.15). Removing theposterior canal increases access to the posterior fossa, butaccess is only slightly increased over that achieved with theretrolabyrinthine approach. Removing the superior canal in-creases access to the middle fossa and petrous apex andreduces the needed retraction of the temporal lobe. The trans-labyrinthine approach does not significantly increase the ac-cess to the area medial to the porus of the internal acousticmeatus over that achieved with the minimal mastoidectomyor retrolabyrinthine approach, but does provide access to theinternal auditory canal. The transcochlear modification, inwhich bone is removed up to the edge of the clivus, doessignificantly increase access to the front of the brainstem andclivus over that achieved with the lesser degrees of bonyresection. The retrosigmoid, the presigmoid minimal mastoid-ectomy, and the retrolabyrinthine approaches were comparedand yielded nearly the same exposure of the cerebellopontineangle, but the retrosigmoid approach did not provide theadditional exposure of the middle fossa and petrous apex thatcould be achieved in the combined supra- and infratentorialpresigmoid approach.

The skin incision is started in the temporal region above thezygoma, and extends above the ear and downward in thesuboccipital area medial to the mastoid process (Figs. 8.14,8.15, and 8.17). The skin flap is reflected forward to the levelof the external auditory canal. The temporal muscle is ele-vated and reflected anteriorly, and the muscles over the mas-toid and suboccipital areas are swept inferiorly. A temporo-occipital craniotomy is performed and the transverse sinus isexposed. After the bone flap is elevated, a mastoidectomy iscarried out without entering the labyrinth. The sigmoid sinusis skeletonized from the sinodural angle to the jugular bulb.Bone is removed superiorly to expose the floor of the middlefossa and the superior petrosal sinus. Trautman’s triangle isexposed in the area lateral to the otic capsule.

The dura mater is then incised along the base of the tem-poral craniotomy, while preserving the junction of the vein of

Labbe with the transverse sinus. The posterior fossa dura isopened anterior to the sigmoid sinus in Trautman’s triangle.The dural incision is extended across the superior petrosalsinus to join the dural incision in the temporal dura. Afterdivision of the superior petrosal sinus, the tentorium is in-cised parallel to and just behind the petrous ridge and supe-rior petrosal sinus. This dural incision is extended from thesite of division of the superior petrosal sinus through themedial edge of the tentorium to the incisura behind where thetrochlear nerve enters the tentorial edge. Care is taken toavoid injury to the IVth cranial nerve in its course near thetentorial margin. The posterior portion of the temporal lobe iselevated and the sigmoid sinus is displaced posteriorly alongwith the cerebellar hemisphere while preserving the junctionof the vein of Labbe with the sigmoid sinus. The sigmoidsinus limits the ability for superior retraction of the temporallobe and can be ligated to improve the exposure if bilateralvenous angiography show adequate communication throughthe torcular to the opposite side (24). The petroclival regioncan be exposed from the middle fossa and tentorial incisura tonear the foramen magnum, although access to the lowerpetroclival region may be limited by the jugular bulb. Thepresigmoid exposure provides a shorter working distance tothe petroclival area and provides multiple angles for dissec-tion. The major arteries in the posterior fossa are easily acces-sible. The exposure can also be combined with a far-lateralapproach (Fig. 8.17).

Subtemporal preauricular infratemporal fossa approach

The subtemporal preauricular infratemporal approach isdirected through the infratemporal and middle fossae to thepart of the anterior surface of the petrous bone located medialto the cochlea and to the petroclival region (Figs. 8.10, 8.13,and 8.18). This description outlines the full extent of theanatomic exposure available through this approach, but it canoften be tailored to a smaller, more limited, approach. Acurvilinear incision starting in the frontal region turns down-ward in front of the ear into the cervical region. The incision

Š

FIGURE 8.16. G–N. Comparison of the retrosigmoid and the various modifications of the presigmoid exposure. G, deepexposure with the minimal mastoidectomy with retraction of the vestibulocochlear and glossopharyngeal nerves, to be com-pared with the retrosigmoid approach shown in C. The exposure is similar to that obtained with the retrosigmoid approach.H, retrolabyrinthine approach in which more extensive drilling of the mastoid has been completed to expose the osseous cap-sule of the semicircular canals. I, the dura has been folded forward after completing the retrolabyrinthine exposure. Theexposure differs little from that obtained with the minimal mastoidectomy exposure shown in F and G. J, the exposure withthe posterior canal partial labyrinthectomy is similar to that achieved with the minimal mastoidectomy. K, the partial laby-rinthectomy has been extended by removing the superior canal in addition to removal of the posterior canal. L, the infraten-torial exposure does not differ significantly from that achieved with the minimal mastoidectomy, as shown in F and G.Removal of the superior canal reduces the required temporal lobe retraction and aids in the exposure along the middle fossafloor and petrous apex. M, translabyrinthine exposure in which the semicircular canals and the vestibule have been removed.This adds the internal auditory canal to the exposure, but does not improve the exposure of the structures medial to themeatus, as compared with the minimal mastoidectomy or even the retrosigmoid approach. N, the facial nerve has been trans-posed posteriorly out of the field and the cochlea has been removed to complete the transcochlear approach. This approachgreatly improves access to the front of the brainstem, clivus, and basilar artery, but is done at the cost of a temporary or per-manent facial paralysis and loss of hearing.

Temporal Bone S249


may be extended downward only to the area just below thetragus if only the petrous apex and upper part of the infra-temporal fossa are to be exposed, but it can be extended ontothe upper neck if a neck dissection is needed. The skin flap isseparated from the underlying tissues and reflected forward.The facial nerve and its major branches are identified distal tothe stylomastoid foramen and followed to the parotid gland.The parotid gland is separated from the masseteric fascia toavoid excessive stretching of the facial nerve at the stylomas-toid foramen (33, 38, 39). The superficial temporalis fascia inwhich the upper facial branches course is separated from thetemporalis muscle and is reflected forward to prevent damageto the branch of the facial nerve to the frontalis muscle as thezygomatic arch is exposed. The zygomatic arch is divided atits anterior and posterior ends, and the temporalis muscle,with the overlying segment of the zygomatic arch, is reflecteddownward. The mandibular condyle and the capsule of thetemporomandibular joint are either dislocated downward orexcised. The temporomandibular joint can be removed in asingle piece for later replacement by dividing the mandibularneck below the condyle and osteotomizing the middle fossafloor around the mandibular fossa (Fig. 8.18). The internalcarotid artery, the internal jugular vein, and the vagus, acces-sory, and hypoglossal nerves may be exposed in the neck ifneeded. The posterior belly of the digastric muscle may bedivided and the styloid process resected.

A frontotemporal craniotomy is then performed. The durais elevated from the floor of the middle fossa to expose andobliterate the middle meningeal artery at the foramen spino-sum and to expose the arcuate eminence, the third trigeminaldivision at the foramen ovale, and the greater petrosal nerve.The greater petrosal nerve is transected if necessary to avoidtraction on the facial nerve. The floor of the middle fossa, includ-ing the lateral and inferior aspects of the superior orbital fissure,and the lateral margin of the foramina ovale may be removed toexpose the structures in the infratemporal fossa.

If needed, bone can be removed medial to the mandibularfossa to expose the eustachian tube and the tensor tympanimuscle, both of which may be resected (Figs. 8.10, 8.13, and8.18). The bone removal is continued inferiorly, exposing theascending portion of the petrous carotid. In this segment, thecarotid artery is surrounded by a periosteal sheath, whichencloses a periarterial venous plexus that is an extension ofthe cavernous sinus. At the entrance of the carotid canal, adense fibrocartilaginous ring encircles the artery. If mobiliza-tion of the artery is required, care must be taken when divid-ing the ring not to damage the IXth cranial nerve that is inclose proximity to the carotid canal as it exits the jugularforamen. After mobilizing the carotid artery and displacing itforward, the petrous apex and the clival region to the level ofthe foramen magnum can be approached medial to and be-hind the artery. During drilling, the very hard cortical bonealong the petrous apex gives place to a crumbly cancellousbone in the region of the clivus, as the dura of the anterior andlateral aspects of the posterior fossa is being exposed. The areaexposed is limited by Meckel’s cave superiorly, by the cochleaand internal auditory canal laterally, by the abducens nerve inits course through the Dorello’s canal medially, and by the

hypoglossal canal inferiorly. If the dura is opened, the struc-tures along the lateral and anterior aspects of the upper me-dulla and lower two-thirds of the pons will be exposed (41).The tentorium can be divided to give access to the upper clivalregion.

Dividing the third trigeminal division above the foramenovale will permit exposure of the junction of the petrous andcavernous carotid along with the structures in the inferolat-eral portion of the cavernous sinus (17, 39). The pterygopal-atine fossa, parapharyngeal space, lateral maxilla, and orbitcan be exposed farther anteriorly. The lateral aspect of thesphenoid bone and the sphenoid sinus can also be ap-proached by removing bone medial to the maxillary nerve atthe root of the pterygoid process.

Postauricular transtemporal approach

The postauricular transtemporal approach is most com-monly selected for lesions that involve the mastoid and tym-panic cavities and track along the nerves and arteries to reachthe middle and infratemporal fossa (Figs. 8.19 and 8.20). It can,however, be tailored at its posterior margin to include aretrosigmoid, far-lateral, or presigmoid exposure of the pos-terior fossa or, at its anterior limits, to include exposure of thepterygopalatine fossa and lateral parts of the maxillary orbitor anterior cranial fossa.

A question mark incision is started behind the hairline inthe temporal region, extending behind the ear over the mas-toid process and continuing inferiorly in front of the sterno-cleidomastoid muscle onto the neck. The skin flap is thenreflected forward and the external auditory canal is divided atthe bone-cartilage junction and closed as a blind sac. Thesternocleidomastoid muscle is detached from the mastoidprocess and reflected inferiorly. The periosteum and posteriorportion of the temporalis muscle are reflected anteriorly, thusexposing the temporal, mastoid, and retromastoid areas. Theposterior belly of the digastric muscle is divided and reflectedinferiorly. At this point, the facial nerve is identified distal tothe stylomastoid foramen and is followed, along with itsmajor branches, into the substance of the parotid gland (5).The internal jugular vein, the carotid bifurcation, and theglossopharyngeal, vagus, accessory, and hypoglossal nervesare exposed and isolated in the neck. This allows for proximalcontrol of the internal carotid artery and ligation of the mainfeeding vessels from the external carotid artery to a neoplasmearly in the procedure.

After this, temporal and/or retromastoid craniotomies maybe performed with a simple mastoidectomy. The remainingskin of the external auditory canal, the tympanic membrane,the malleus, incus, and stapes arch (leaving the footplate) areremoved. The facial nerve is completely skeletonized from thegeniculate ganglion to the stylomastoid foramen.

If exposure of the jugular foramen and lower clival regionis desired, a new facial canal is created by drilling a groove inthe bone of the anterior attic wall, between the geniculateganglion and the root of the zygoma. The facial nerve iscarefully freed at the stylomastoid foramen, while leavingsome of the surrounding connective tissue attached to the

S250 Rhoton


nerve, and the nerve is transposed anteriorly into the newbony groove of the epitympanum and imbedded for its pro-tection into the parotid tissue (5).

The dura of the middle fossa and the sigmoid sinus fromthe sinodural angle to the jugular bulb is skeletonized. Thenthe sigmoid sinus and the jugular vein are ligated in thissequence, and the sigmoid sinus divided. Part of the wall ofthe sinus, bulb, and/or vein may be excised to increase theexposure. This allows for dissection of the lower cranial

nerves at the jugular foramen, as well as for their mobilizationand posterior displacement if necessary. The posterior mobi-lization of the lower cranial nerves allows for a direct expo-sure of the structures along the lateral and anterior aspects ofthe medulla and lower pons without the necessity for brainretraction. Dissection in the area of the jugular foramen hasproven to be extremely difficult, as the lower cranial nervesare particularly fragile and difficult to isolate from the sur-rounding tissues.

FIGURE 8.17. A–D. Combinedpresigmoid and far-lateralapproach. A, the insert showsthe site of the scalp incision andmastoid tip. The scalp flap hasbeen reflected forward. Themastoidectomy exposes thedense cortical bone housing thesemicircular canals. The boneflap is outlined. The occipitalartery courses backwardbetween the digastric andsuperior oblique. B, enlargedview. The tympanic segment ofthe facial nerve courses belowthe lateral canal. The chordatympani arises from the mastoidsegment of the facial nerve. Themastoid antrum, which has beendrilled away, opens through theaditus into the epitympanic partof the tympanic cavity. C, thepresigmoid and temporal duralincisions have been outlined. D,the temporal and presigmoiddura has been opened. One goalof the procedure is to preservethe vein of Labbe, whichempties into the transversesinus. A., artery; A.I.C.A.,anteroinferior cerebellar artery;Atl-Occip., atlanto-occipital;Cap., capitis; Car., carotid;Chor., chorda; Cist., cisternal;CN, cranial nerve; Epitymp.,epitympanic; For., foramen;Gang., ganglion; Genic.,geniculate; Hypogl., hypoglossal;Inf., inferior; Jug., jugular; Laby.,labyrinthine; Lat., lateral; Lev.,levator; M., muscle; Meat.,meatal; Memb., membrane;Men., meningeal; N., nerve;Obl., oblique; Occip., occipital;P.C.A., posterior cerebral artery;P.I.C.A., posteroinferior cerebellar artery; Plex., plexus; Post., posterior; Rec., rectus; S.C.A., superior cerebellar artery; Scap.,scapula; Seg., segment; Semicirc., semicircular; Sig., sigmoid; Sp., spine; Suboccip., suboccipital; Sup., superior; Temp.,temporal; Trans., transverse; Tymp., tympani, tympanic; V., vein; Vert., vertebral; Vest., vestibular.

Temporal Bone S251


Exposure of the middle clival structures requires removal ofthe bony labyrinth, as described for the translabyrinthine ap-proach. The internal auditory canal is exposed, the facial nerveidentified, and the cochlear and vestibular nerves divided. Thegreater superficial petrosal nerve is sectioned at its origin fromthe geniculate ganglion. The facial nerve is freed from allits attachments in the temporal bone and reflected posteriorly.The bony portion of the external auditory canal and the tym-panic bone are drilled away, exposing the ascending portion ofthe intrapetrous carotid artery medial to the eustachian tube.

The dissection is continued by drilling away the cochlea,starting at its basal turn, to expose part of the horizontalsegment of the petrous carotid artery. Anterior displacementof the carotid artery and removal of the cochlea provides awide exposure of the lateral and anterior portions of the pons

and medulla. This exposure extends from the inferior aspectof the trigeminal ganglion to the foramen magnum. The ex-posure may be carried medially into the clivus and retropha-ryngeal space and anteriorly to expose the mucosa of thesphenoid sinus.

If the approach is to be extended to the parasellar andparasphenoidal areas, the zygomatic arch is divided and re-flected inferiorly with the masseter muscle. The temporalismuscle is separated from its attachment to the coronoid pro-cess of the mandible and reflected anteriorly and superiorly.A temporal craniotomy is then performed, and extensive boneis removed along the whole lateral aspect of the middlecranial fossa. The ascending ramus of the mandible is eitherdisplaced anteriorly or resected, and the petrous carotid isexposed distally to the proximal portion of the intracavernous

FIGURE 8.17. E–H. Combinedpresigmoid and far-lateralapproach. E, the dural incision hasbeen extended throughTrautman’s triangle and across thesuperior petrosal sinus andtentorium, taking care to preservethe vein of Labbe and thetrochlear nerve. The semicircularcanals have been opened. F,enlarged view. The posterior canalfaces the posterior fossa lateral tothe internal acoustic meatus. Thesuperior canal projects upward,below the arcuate eminence,toward the floor of the middlefossa. The lateral canal is a usefullandmark for identifying thetympanic segment of the facialnerve, which courses between thecanal and the stapes sitting in theoval window. The epitympanicarea opens through the aditus intothe mastoid antrum. G, thelabyrinthectomy has beencompleted and the dura lining themeatus opened to expose thecisternal, meatal, labyrinthine,tympanic, and mastoid segmentsof the facial nerve. The SCAcourses above the trigeminalnerve. H, enlarged view along theopened tentorial incisura. Theoculomotor and trochlear nervescourse between the PCA and SCA.The SCA rests against the uppersurface of the trigeminal nerve.

S252 Rhoton


segment after removing the cartilaginous portion of the eu-stachian tube. The cavernous sinus can be approached and theintracavernous carotid artery exposed by dividing the man-dibular segment of the trigeminal nerve. The approach canalso be extended to the retrosigmoid area and down thevertebral artery to the C1 to C2 level, or to the suboccipitaltriangle for a far-lateral or transcondylar exposure. The lateralorbit and pterygopalatine fossa can be accessed at the anteriorlimit of the exposure.

DISCUSSION

Pathologies can arise anywhere within the petroclival re-gion and frequently are not restricted to a single anatomiccompartment of the cranial base. Involvement of multiplecranial nerves and arteries occurs because cranial base tumors

tend to achieve considerable size before producing clinicalmanifestation (32). The distinction between the benign ormalignant tumors in this area is not rigid because manybenign tumors can have a very invasive characteristic. Theselection of the best surgical approach depends on the loca-tion, extension, size, and nature of the pathology.

An advantage of these approaches directed through thetemporal bone to the petroclival area is that they reach thearea through tissue planes outside the oropharynx. They pro-vide another route by which anterior intradural lesions situ-ated medial to the nerves entering the internal acoustic me-atus and jugular foramen can be approached without enteringthe nasopharynx. They also provide an avenue of exposurefor lesions that involve the temporal and sphenoid bones inaddition to the clivus. One or a combination of the lateral

FIGURE 8.17. I–L. Combined presigmoid and far-lateral approach. I, the insert shows the site of the additional skin incisionneeded to add a retrosigmoid craniotomy and far-lateral approach. The scalp flap has been reflected to expose the suboccipi-tal triangle located between the superior and inferior oblique and the rectus capitis posterior major and in the depths ofwhich the vertebral artery courses with a dense venous plexus. J, the venous plexus has been removed to expose the marginsof the suboccipital triangle. K, the rectus capitis posterior major and the inferior oblique have been reflected medially andthe superior oblique laterally to expose the vertebral artery and surrounding venous plexus behind the atlanto-occipital joint.L, the venous plexus has been removed to expose the vertebral artery coursing with the C1 nerve behind the atlanto-occipitaljoint and across the upper edge of the posterior atlantal arch.

Temporal Bone S253


approaches is frequently used to expose intra- or extraduralclival lesions that also involve the temporal and sphenoidbones. They also provide access to the anterior aspect of themidbrain, pons, and medulla and to the cerebellopontineangle and nerves in the posterior fossa. They may also pro-vide better access to the temporal bone, jugular foramen, andpetrous segment of the internal carotid artery than the otheranterior or posterior approaches. The area may be approachedfrom directly lateral through the mastoid, labyrinth, and co-chlea, as in the translabyrinthine and transcochlear approach-es; from above through a subtemporal middle fossa route;from behind in the retrosigmoid suboccipital approach; orfrom multiple directions using such combined supra- andinfratentorial approaches as the presigmoid approach, towhich a translabyrinthine or transcochlear approach maybe added. Alternative or extended approaches, most ofwhich include some route through the mastoid and petrousparts, include the anterior transpetrosal, the subtemporal pre-auricular infratemporal, and the far-lateral transcondylarapproach.

The retrosigmoid suboccipital approach, described in thechapter on the cerebellopontine angle, offers a wide view ofthe cerebellopontine angle and of the intradural structuresbehind the ipsilateral lower clivus, but the dural surface of thepetrous apex, upper clivus, and tentorial incisura are not wellseen from this exposure (26, 35, 36, 46) (Figs. 8.15 and 8.16).Removal of posterior wall of the internal auditory canalthrough the retrosigmoid provides access to the contents ofthe meatus as far lateral as the vertical and transverse crests.The vestibule can be opened if needed to remove a tumorextending into the labyrinth. Care is required to avoid injuryto the posterior semicircular canal and common crus if there isthe possibility of preserving hearing (29). The retrosigmoidapproach provides easy access to the intradural part of cranialnerves V, VII, VIII, and IX through XII. It also provides access

to the nerve-related segments of the arteries of the posteriorcirculation. The vertebrobasilar junction can be exposed insome cases, although the lower cranial nerves and the jugulartubercle are frequent obstacles. Retraction of the pons andworking between the cranial nerves is necessary to reach theorigin of the AICA from the basilar artery. The far lateralmodification of the retrosigmoid approach, described in thechapter on the far lateral approach, was devised to provide abetter exposure of the lateral and anterior aspects of thecervicomedullary junction (45).

The presigmoid approach (1, 8, 32) combines a supra- andinfratentorial exposure with various degrees of petrousec-tomy, while preserving the junction of the vein of Labbe withthe transverse sinus (Figs. 8.14-8.17). The amount of resectionof the petrous bone can vary from a retrolabyrinthine minimalmastoidectomy exposure to a translabyrinthine or transco-chlear exposure with posterior displacement of the facialnerve. In selected cases, where angiography shows patency ofthe communication between the two transverse sinuses acrossthe midline, the sigmoid sinus can be ligated to improve theexposure (24). Preservation of the drainage of the vein ofLabbe and avoidance of excessive temporal lobe retraction aremajor goals of this approach to the upper clival region. Ap-proaching the structures in the inferior petroclival space maybe restricted by the jugular bulb, which could be overcome bydivision of the sigmoid sinus or by working posterior to it(36). The major advantages of this approach are the shorterworking distance to clival lesions and the various angles fordissection that are provided. The approach provides access tothe ipsilateral cranial nerves III through XII and to the majorarteries in the posterior circulation. A major drawback to thisexposure is provided by the anatomic variants, describedbelow, that limit the size of the exposure through Trautman’striangle and the labyrinth.

FIGURE 8.17. M and N, combinedpresigmoid and far-lateral approach.M, a suboccipital craniotomy hasbeen completed, the posterior archand posterior ramus of thetransverse process of the atlasremoved, and the dural incision hasbeen outlined. The posteriormeningeal artery arises before thevertebral artery penetrates the dura.The C1 nerve root adheres to thelower margin of the vertebralartery. N, the dura has been openedand the nerves passing toward thejugular foramen exposed. Bone hasbeen removed above the atlanto-occipital joint to expose thehypoglossal nerve in the hypoglossalcanal. The accessory rootlets crossthe jugular tubercle on their wayto the jugular foramen.

S254 Rhoton


FIGURE 8.18. Preauricularsubtemporal-infratemporal fossaapproach. A, the scalp incision is posi-tioned so that a frontotemporal crani-otomy can be completed. The opera-tion is often completed with anincision that extends downward onlyto the level of the tragus. However, itcan be extended if a neck dissection isneeded. The scalp flap has beenreflected forward, taking care to pro-tect the branches of the facial nerve.B, the temporalis muscle has beenrefracted forward and the craniotomycompleted. The mandibular condyleand fossa and a portion of the zygo-matic arch were removed in a singlepiece, as shown in the insert, and themiddle fossa floor removed. C, expo-sure after removal of the middle fossafloor lateral to the foramen ovale andbefore resection of the tensor tympanimuscle. The lower orifice of thecarotid canal is located in front of thejugular foramen. The eustachian tube,which passes across the front of thepetrous carotid, has been opened. D,the tensor tympani and eustachiantube have been resected to expose thehorizontal segment of the petrouscarotid. E, the internal carotid arteryhas been reflected forward and thepetrous apex drilled to expose theposterior fossa dura and the inferiorpetrosal sinus coursing along the pet-roclival fissure. F, the dura facing thepetrous apex has been opened and thevertebral arteries and AICA exposed.This exposure is directed through thepetrous apex medial to the cochleaand jugular foramen and does not riskloss of facial nerve function or hear-ing, as do the approaches directedthrough the petrous apex that requirefacial nerve transposition and resec-tion of the labyrinth. A., artery;A.I.C.A., anteroinferior cerebellarartery; Brs., branches; Car., carotid;CN, cranial nerve; Eust., eustachian;Gang., ganglion; Gl., gland; Gr., great-er; Inf., inferior; Int., internal; Jug.,jugular; M., muscle; Max., maxillary;Men., meningeal; Mid., middle; N.,nerve; Pet., petrosal, petrous; Post.,posterior; Temp., temporal; Tens., ten-sor; TM., temporomandibular; Trig.,trigeminal; Tymp., tympani; V., vein;Vert., vertebral; Zygo., zygomatic.

Temporal Bone S255


The translabyrinthine approach provides access to the facialnerve from its origin at the brainstem to the stylomastoidforamen, and exposure of the contents of the internal auditorymeatus (Fig. 8.6) (12, 14). The lateral surface of the pons, theinferior aspect of the origin of the trigeminal nerve, and thefacial and vestibulocochlear nerve complexes are well visual-ized, but exposure of the region inferior to the jugular bulb,above the trigeminal nerve, and anterior to the internal acous-

tic meatus is usually poor. The extent of exposure achievedwith the translabyrinthine approach is dependent on severalanatomic factors. A high jugular bulb, an anteriorly placed orlarge sigmoid sinus, or a low middle fossa plate may severelyrestrict the exposure (22, 27).

The transcochlear approach shares similar limitations withthe translabyrinthine exposure, although the posterior trans-position of the facial nerve in the transcochlear approach

FIGURE 8.19. A–D. Anatomic basis ofthe postauricular transtemporalapproach. A, the incision sweeps widelyaround the posterior margin of the earso that a retrosigmoid, presigmoid, andfar-lateral exposure can be obtainedbehind the ear, and a subtemporal,infratemporal, pterygopalatine, andorbital exposure can be obtained infront of the ear. B, the scalp flap hasbeen reflected forward, the externalcanal transected, and the parotid glandand superficial branches of the facialnerve exposed. C, thesternocleidomastoid muscle has beenreflected. The neck dissection exposesthe internal jugular vein, C1 transverseprocess, and the glossopharyngeal,vagus, accessory, and hypoglossalnerves. The accessory nerve is retractedforward. D, the parotid gland has beenremoved to expose the temporofacialand cervicofacial trunks of the facialnerve and the temporomandibular joint.The splenius capitis muscle has beenreflected downward to expose thesuperior and inferior oblique muscles,which insert on the transverse processof C1 and border the suboccipitaltriangle in which the vertebral arterycourses. A., artery; Alv., alveolar; Aur.,auricular; Br., branch; Brs., branches;Cap., capitis; Car., carotid; Cerv.,cervical; Chor., chorda, choroid; CN,cranial nerve; Coch., cochlear; Cond.,condyle; Endolymph., endolymphatic;Eust., eustachian; Ext., external; Fac.,facial; Gang., ganglion; Genic.,geniculate; Gl., gland; Gr., greater;Hypogl., hypoglossal; Inf., inferior;Infraorb., infraorbital; Infratemp.,infratemporal; Int., internal; Jug.,jugular; Laby., labyrinthine; Lat., lateral; Lev., levator; M., muscle; Mandib., mandibular; Mast., mastoid; Max., maxillary;Med., medial; N., nerve; Obl., oblique; Occip., occipital; Pal., palatini; P.C.A., posterior cerebral artery; Ped., peduncle; Pet.,petrosal, petrous; P.I.C.A., posteroinferior cerebellar artery; Plex., plexus; Post., posterior; Proc., process; Pteryg., pterygoid;Pterygopal., pterygopalatine; Rec., rectus; S.C.A., superior cerebellar artery; Scap., scapula; Seg., segment; Semicirc.,semicircular; Sig., sigmoid; Sphen., sphenoid; Splen., splenus; Sternocleidomast., sternocleidomastoid; Sup., superior; Superf.,superficial; Symp., sympathetic; Temp., temporal; Tens., tensor; TM., temporomandibular; Trans., transverse; Tymp., tympani,tympanic; V., vein; Vel., veli; Vert., vertebral; Vest., vestibular.

S256 Rhoton


allows better visualization of the structures anterior to theinternal auditory canal (15, 16). The area of exposure is verynarrow and restricted by the maintenance of the bony externalauditory canal, but can be increased by resecting the posteriorpart of the canal. Transposition of the facial nerve may befollowed by a transient or permanent facial palsy.

The subtemporal anterior transpetrosal approach uses ex-tradural resection of the anterior petrous pyramid via a tem-poral craniotomy (Figs. 8.12 and 8.13). It may be combinedwith zygomatic resection to increase access to the floor of themiddle fossa (20). The area of the petrous apex removalextends from just medial to the internal auditory canal and

cochlea to the petrous apex and petroclival junction, and fromthe petrous ridge posteriorly to the carotid canal anteriorly. Asignificant degree of temporal lobe retraction may be re-quired. This may be reduced by using a frontotemporal cra-niotomy with zygomatic resection. Although only a smallwindow in the petrous bone is provided, exposure can beexpanded by dividing the adjacent part of the tentorium. Thelateral and anterior surfaces of the pons and the upper clivusand adjacent part of the cavernous sinus can be approachedthrough this route (Fig. 8.13). The facial, vestibulocochlear,trigeminal, and abducens nerves can be identified. The pe-trous carotid may limit the surgeon’s line of vision and restrict

FIGURE 8.19. E–H. Anatomic basis ofthe postauricular transtemporal approach.E, a segment of the mandibular ramus hasbeen removed to expose the upper andlower head of the lateral pterygoid andthe maxillary artery in the infratemporalfossa. The inferior alveolar canal andnerve have been exposed. F, themandibular ramus, in front of the inferioralveolar canal, has been removed toprovide a wider exposure of theinferotemporal fossa. The upper head ofthe lateral pterygoid muscle passesbackward from the inferotemporalsurface of the greater sphenoid wing andthe lower head passes upward from thelateral pterygoid plate. Both heads inserton the mandibular neck and the jointcapsule. The superficial head of themedial pterygoid muscle passes from themaxillary tuberosity and pterygoid plateto the mandibular angle. The deep headof the medial pterygoid arises from thepterygoid fossa between the pterygoidplates. G, enlarged view of theinfratemporal area after removal of themandibular condyle and lateral pterygoidmuscles. The branches of the mandibularnerve are exposed below the foramenovale. The largest branches are thelingual and superior alveolar nerves,which are predominantly sensory. Theauriculotemporal nerve arises as tworoots, which often pass around themiddle meningeal artery before joining.H, the pterygoid muscles, a segment ofthe maxillary artery, and the mandibularand facial nerve branches have beenreflected or removed to expose theinternal jugular vein exiting the jugularforamen on the medial side of the

stylomastoid foramen, the internal carotid artery ascending to enter the carotid canal, the tensor and levator veli palatinidescending from their origin bordering the eustachian tube, and the terminal segment of the maxillary artery entering thepterygopalatine fossa.

Temporal Bone S257


access to the inferior part of the petroclival region, but thisrestriction may be overcome with anterior mobilization of theartery (39, 41). The approach provides access to the anterioraspect of the brainstem and basilar artery in the area betweenthe trigeminal nerve above and the facial and vestibuloco-chlear nerves below. In approaching the basilar arterythrough this route, the size and location of the lesion inrelation to the petrous ridge is critical. The trigeminal nervecan be mobilized to improve the exposure, although this mayresult in postoperative facial hypesthesia (19, 20). The anteriortranspetrosal approach can be used alone for extradural pathol-ogies restricted to the petrous apex or as a surgical step toapproaching intradural pathologies in the petroclival region. Itprovides a route for resecting extradural lesions that extend fromthe level of the trigeminal nerve to the foramen magnum.

Removal of the posterior part of the petrous pyramid hasbeen used for acoustic neuroma removal as part of extendedapproaches directed through the middle fossa (21, 28, 42, 43)(Fig. 8.12). The extended approaches combine different de-grees of resection of the bony labyrinth with the subtemporaltranstentorial routes. Extending the resection of the petrousbone posteriorly over the mastoid and the bony labyrinthexposes the whole intrapetrous course of the facial nerve, andprovides access to the cerebellopontine angle by a combina-tion of subtemporal, translabyrinthine, and presigmoid routes(Figs. 8.12 and 8.13) (9).

The subtemporal preauricular infratemporal approachreaches the skull base from an anterolateral direction (Figs.8.10, 8.13, and 8.18). Division of the zygomatic arch, resectionor displacement of the mandibular condyle, and extensive

FIGURE 8.19. I–L. Anatomic basis of thepostauricular transtemporal approach. I, amastoidectomy has been completed toexpose the semicircular canals and themastoid segment of the facial canal. Theendolymphatic sac sits under the presigmoiddura. J, the external canal has been resectedto expose the structures in the tympaniccavity. The tympanic segment of the facialnerve courses between the lateralsemicircular canal and the stapes sitting inthe oval window. The chorda tympani arisesfrom the mastoid segment of the facialnerve, passes forward along the innersurface of the tympanic membrane and theneck of the malleus to enter its anteriorcanaliculus, exits the skull along thepetrotympanic suture, and joins the lingualnerve in the infratemporal fossa. Thepromontory overlies the basal turn of thecochlea. The tendon of the tensor tympanimuscle makes a right-angle turn around thetrochleiform process to insert on themalleus. K, the incus and malleus have beenremoved while preserving the stapes andthe tensor tympani muscle. The petrouscarotid has been exposed. The nervesexiting the jugular foramen have beenretracted forward to expose the hypoglossalnerve exiting the hypoglossal canal. L, afrontotemporal craniotomy has beencompleted and the floor of the middlecranial fossa removed. The semicircularcanals have been exposed above the jugularbulb and the stapes has been removed fromthe oval window. The maxillary nerve hasbeen exposed in the pterygopalatine fossa.The membranous wall of the eustachiantube has been opened to expose the tube’sopening into the nasopharynx.

S258 Rhoton


FIGURE 8.19. M–R. Anatomic basis ofthe postauricular transtemporal approach.M, a retrosigmoid craniotomy has beencompleted and the nerves in thecerebellopontine angle exposed. Thevestibulocochlear nerve has beendepressed to expose the facial nerve. N,the facial nerve has been reflectedforward out of the facial canal. Thepromontory has been drilled to exposethe cochlea and the vestibule. Both endsof the semicircular canals open into thevestibule, as does the basal turn of thecochlea. The jugular bulb has beenremoved to expose the jugular fossa inwhich the bulb resides. The jugular bulbis located below the vestibule. The nervesexiting the jugular foramen have beenreflected backward to expose thehypoglossal nerve exiting the hypoglossalcanal. The nerves passing through thejugular foramen and hypoglossal canalexit the skull on the medial side of theinternal jugular vein and descendbetween the internal carotid artery andinternal jugular vein. O, the bone abovethe occipital condyle has been drilled toexpose the hypoglossal nerve in thehypoglossal canal. P, the posterior wall ofthe internal acoustic meatus has beenremoved to provide this presigmoidinferolateral view of the nerves in theinternal meatus. The cochlear nerveseparates off the main bundle of thevestibulocochlear nerve and penetratesthe modiolus. The inferior vestibularnerve divides into the singular nerveto the posterior ampullae and a branch tothe saccule. The superior vestibular nerveinnervates the superior and lateralampullae and sends a branch to theutricle. Q, the medial wall of the jugularfossa has been removed and the nervespassing through the jugular foramen havebeen exposed. The glossopharyngealnerve passes through the foramenanterior to the vagus and accessorynerves. A large superior petrosal veinascends to the superior petrosal sinus. R,the glossopharyngeal, vagus, andaccessory rootlets arise behind and thehypoglossal rootlets arise anterior to theinferior olive.

Temporal Bone S259


FIGURE 8.19. S–X. Anatomic basis of the postauricular transtemporal approach. S, enlarged view of the medial wall of the tympanic cav-ity before mobilizing the facial nerve. The stapedial muscle passes forward from the pyramidal eminence below the facial nerve andattaches on the neck of the stapes. The tensor tympani muscle passes backward and laterally, giving rise to a narrow tendon that makes asharp turn around the trochleariform process at the lateral end of its semicanal to insert on the handle of the malleus. The basal turn ofthe cochlea is located deep to the promontory. The tympanic segment of the facial nerve courses above the stapes. T, enlarged view ofthe labyrinth. The semicircular canals have been unroofed and the stapes has been removed from the oval window. The round window islocated below and behind the oval window. U, the facial nerve has been reflected forward out of the facial canal and the vestibule hasbeen opened. The ampullae of the superior and the lateral canal open into the vestibule anteriorly and are innervated by the superiorvestibular nerve. Only the upper edge of the superior canal was preserved in opening the vestibule. The ampullae of the posterior canal islocated at its lower end and is innervated by the singular branch of the inferior vestibular nerve. V, a probe is directed through the vesti-bule to the inner surface of the membrane covering the round window, which is located behind and below the oval window. W,enlarged view of the labyrinth after opening the promontory to expose the cochlea. The jugular bulb is located below the vestibule andsemicircular canals and the lateral genu of the internal carotid artery in position below the cochlea. The cochlea wraps around the modi-olus through which the branches of the cochlear nerve are distributed to the cochlear duct. X, the temporal lobe has been elevated toexpose the internal carotid, PCA, and SCA in the basal cisterns. The dura has been elevated from the lateral wall of the cavernous sinus.

S260 Rhoton


resection of the lateral part of the middle fossa floor exposesthe infratemporal fossa, the nasopharynx, the para- and ret-ropharyngeal areas, and the ethmoid, sphenoid, and maxil-lary sinuses. The approach also provides access to the uppercervical and petrous carotid. The cavernous sinus also can beapproached through its lateral and basal aspects. Anteriordisplacement of the petrous carotid allows direct access to theclivus and for extensive resection of the petrous bone medialto the cochlea. This exposes the extradural clival region fromthe level of the trigeminal nerve to the foramen magnum (33,36, 38, 39). The approach can also provide access to the intra-dural space ventral to the brainstem (41). The exposure of thecerebellopontine angle and foramen magnum is limited be-cause the approach is carried anterior and medial to cranialnerves VII through XII and the cochlea is not resected (36).Anterior transposition of the petrous carotid artery allowsunhindered exposure of the origin of the AICA and the ver-tebrobasilar junction. The approach could be used as an alter-

native lateral route to vascular lesionsof the midbasilar artery or at the ver-tebrobasilar junction, when these le-sions cannot be exposed through ei-ther the retromastoid or subtemporaltranstentorial approaches.

The postauricular transtemporal ap-proach, which combines a transco-chlear exposure with an infratemporalapproach, may be used as an alterna-tive to the preauricular infratemporalapproach when the pathology involvesthe mastoid and the infratemporalfossa and extends to the facial recess,hypotympanic area, and jugular bulb(5, 6, 34) (Figs. 8.19 and 8.20). The struc-tures of the lower and middle clivuscan be exposed without the need forbrain retraction. The facial nerve is dis-

placed anterosuperiorly and the sigmoid sinus ligated and divided.Displacement of the facial nerve from its bony canal seriouslyinterferes with its vascular supply and temporary or permanentloss of function is to be expected (33). Resection of the jugular bulballows for exposure of the lower cranial nerves in the jugular fora-men. Mobilization of the nerves in the medial part of the jugularforamen is extremely difficult and nerve damage is likely to occur ifit is attempted. The lateral and anterior surfaces of the lower pons,medulla, and cervicomedullary junction are well exposed. The ex-tent of exposure of the major arteries is dependent on the differentanatomic variants and direction of displacement of the vessels.Exposure of the structures of the middle clivus requires posteriorfacial nerve displacement and drilling of the labyrinth with conse-quent destruction of any residual hearing. The lateral and part ofthe anterior surfaces of the pons can be exposed up to the point ofemergence of the trigeminal nerve. Exposure of the superior petro-clival space requires that the transtemporal exposure be combinedwith a subtemporal exposure. The transtemporal approach can

FIGURE 8.19. Y and Z, anatomicbasis of the postauriculartranstemporal approach. Y,overview before opening the dura.The postauricular approach offersthe potential for providingretrosigmoid, presigmoid, and far-lateral exposures and can be usedto access the infratemporal andpterygopalatine fossae, the orbit,and the subtemporal areas. In thiscase, the exposure extends from theretrosigmoid area forward to theorbit. The maxillary sinus has beenopened below the orbital floor. Z,overview of exposure after openingthe dura.

Temporal Bone S261


FIGURE 8.20. A–F. Postauricular transtemporal approach. This exposure includes the transtemporal and infratemporal approaches incombination with a craniotomy. A, the scalp flap has been reflected forward to expose the sternocleidomastoid, parotid gland, and thegreater auricular nerve. B, the external canal has been divided to reflect the flap forward for a parotid and neck dissection that exposesthe facial nerve and its trunks, the posterior digastric belly, and the internal jugular vein. C, the mastoidectomy has been completed toexpose the presigmoid dura, the sigmoid sinus, and the semicircular canals. The mandibular condyle has been resected to provide accessto the infratemporal fossa. D, a temporo-occipital craniotomy has been completed, the zygomatic arch opened, and the temporalis mus-cle reflected to expose the maxillary artery and pterygoid muscles in the infratemporal fossa. E, enlarged view of the temporal and infra-temporal exposures. The posterior wall of the external canal has been removed. The auriculotemporal branch of the mandibular nerve isoften split into two rootlets by the middle meningeal artery. F, enlarged view of the tympanic cavity. The anterior part of the lateral semi-circular canal is located above the tympanic segment of the facial nerve. The promontory overlies the basal cochlear turn. A., artery; Ac.,acoustic; Aur., auricular; Bas., basilar; Car., carotid; Chor., chorda; CN, cranial nerve; Cond., condyle; Ext., external; Gl., gland; Gr., great-er; Inf., inferior; Int., internal; Jug., jugular; Lat., lateral; M., muscle; Mandib., mandibular; Mast., mastoid; Max., maxillary; Mid., middle;Men., meningeal; N., nerve; Pet., petrosal, petrous; Proc., process; Seg., segment; Semicirc., semicircular; Sig., sigmoid; Sternocleidomast.,sternocleidomastoid; Sup., superior; Temp., temporal; Trans., transverse; Tymp., tympani, tympanic; V., vein; Vert., vertebral.

S262 Rhoton


FIGURE 8.20. G–L. Postauricular transtemporal approach. G, the external canal has been resected in preparation forexposing the petrous carotid. H, the junction of the cervical and petrous carotid has been exposed in the area below thepromontory. The lateral margin of the stylomastoid and jugular foramina have been removed to expose the jugular bulbbelow the semicircular canals. I, the mandibular nerve has been exposed below the foramen ovale. A more extensiveexposure of the petrous carotid has been completed so that the artery can be reflected forward out of the carotid canalto provide access for drilling of the petrous apex. J, the petrous carotid has been reflected forward and the petrous apexremoved to expose the clivus and inferior petrosal sinus. K, the facial nerve has been moved out of the facial canal, anda total labyrinth and petrous apicectomy have been completed. L, a segment of the sigmoid sinus and the jugular bulbhave been removed to expose the nerves passing through the jugular foramen. The dura has been opened and the facialnerve displaced posteriorly. The temporal lobe has been elevated to expose the subtemporal area while preserving thevein of Labbe.

Temporal Bone S263


easily be extended to the infratemporal fossa, and the same expo-sure provided by the preauricular approach can be achieved. Whenthis approach is combined with an infratemporal fossa exposureand anterior displacement of the intrapetrous carotid artery, thepetrous part of the temporal bone can be completely removed,providing the widest possible exposure of the petroclival region(Figs. 8.19 and 8.20). The retrosigmoid, far-lateral, and transcondylarexposures can be obtained at the posterior margin of the exposure,and the anterior limit can be extended to include the pterygopala-tine fossa and lateral part of the maxilla, orbit, and anterior cranialfossa.

Extensive removal of lesions involving the skull base fre-quently require reconstruction of the resultant bony, neural,and dural defects. The presence of cerebrospinal fluid leaksand the close proximity to contaminated spaces of the oro- ornasopharynx increases the risks of meningitis. Opened sinusesshould be obliterated, dural incisions and openings should besutured and sealed, nerves should be reanastomosed or grafted,and devascularized grafts of bone or dura should be coveredwith vascularized tissue whenever possible.

Reprint requests: Albert L. Rhoton, Jr., M.D., Department of Neuro-logical Surgery, University of Florida Brain Institute, P.O. Box 100265,100 South Newell Drive, Building 59, L2-100, Gainesville, FL32610-0265.

REFERENCES

1. Al-Mefty O, Fox JL, Smith RR: Petrosal approach for petroclivalmeningiomas. Neurosurgery 22:510–517, 1988.

2. Brackmann DE: The middle fossa approach, in Sekhar LN,Janecka IP (eds): Surgery of Cranial Base Tumors. New York, RavenPress, 1993, pp 367–377.

3. Brackmann DE: Translabyrinthine/transcochlear approaches, inSekhar LN, Janecka IP (eds): Surgery of Cranial Base Tumors. NewYork, Raven Press, 1993, pp 351–365.

4. de Oliveira E, Rhoton AL Jr, Peace D: Microsurgical anatomy ofthe region of the foramen magnum. Surg Neurol 24:293–352,1985.

5. Fisch U, Pillsbury HC: Infratemporal fossa approach to lesions inthe temporal bone and base of the skull. Arch Otolaryngol 105:99–107, 1979.

6. Fisch U, Fagan P, Valavanis A: The infratemporal fossa approachfor the lateral skull base. Otolaryngol Clin North Am 7:513–552,1984.

7. Gantz BJ, Fisch U: Modified transotic approach to the cerebel-lopontine angle. Arch Otolaryngol 109:252–256, 1983.

8. Hakuba A, Nishimura S, Inoue Y: Transpetrosal-transtentorialapproach and its application in the therapy of retrochiasmaticcraniopharyngiomas. Surg Neurol 24:405–415, 1985.

9. Hakuba A, Nishimura S, Jang BJ: A combined retroauricular andpreauricular transpetrosal-transtentorial approach to clivus me-ningiomas. Surg Neurol 30:108–116, 1988.

10. Harris FS, Rhoton AL Jr: Anatomy of the cavernous sinus: Amicrosurgical study. J Neurosurg 45:169–180, 1976.

11. Hitotsumatsu T, Rhoton AL Jr: Unilateral upper and lower sub-total maxillectomy approaches to the skull base: Microsurgicalanatomy. Neurosurgery 46:1416–1453, 2000.

12. Hitselberger WE, House WF: Surgical approaches to acoustictumors. Arch Otolaryngol 84:286–291, 1966.

13. House WF: Middle cranial fossa approach to the petrous pyra-mid. Arch Otolaryngol 78:460–469, 1963.

14. House WF: Evolution of transtemporal bone removal of acoustictumors. Arch Otolaryngol 80:731–742, 1964.

15. House WF, Hitselberger WE: The transcochlear approach to theskull base. Arch Otolaryngol 102:334–342, 1976.

16. House WF, De la Cruz A, Hitselberger WE: Surgery of the skullbase: Transcochlear approach to the petrous apex and clivus.Otolaryngology 86:770–779, 1978.

17. Inoue T, Rhoton AL Jr, Theele D, Barry ME: Surgical approachesto the cavernous sinus: A microsurgical study. Neurosurgery26:903–932, 1990.

18. Katsuta T, Rhoton AL Jr, Matsushima T: The jugular foramen:Microsurgical anatomy and operative approaches. Neurosurgery41:149–202, 1997.

19. Kawase T, Shiobara R, Toya S: Anterior transpetrosal-transtentorialapproach for sphenopetroclival meningiomas: Surgical method andresults in 10 patients. Neurosurgery 28:869–876, 1991.

20. Kawase T, Toya S, Shiobara R, Mine T: Transpetrosal approach foraneurysms of the lower basilar artery. J Neurosurg 63:857–861, 1985.

21. King TT, Morrison AW: Translabyrinthine and transtentorial re-moval of acoustic nerve tumors: Results in 150 cases. J Neurosurg52:210–216, 1980.

22. King TT, Morrison AW: Translabyrinthine operation for the re-moval of acoustic nerve tumors, in Schmidek HH, Sweet WH(eds): Operative Neurosurgical Techniques. New York, W.B.Saunders Co., 1988, vol 1, pp 685–704.

23. Lister JR, Rhoton AL Jr, Matsushima T, Peace D: Microsurgicalanatomy of the posterior inferior cerebellar artery. Neurosurgery10:170–199, 1982.

24. Malis LI: Surgical resection of tumors of the skull base, in WilkinsRH, Rengachary SS (eds): Neurosurgery. New York, McGraw-Hill,1985, vol 1, pp 1011–1021.

25. Matsushima T, Rhoton AL Jr, de Oliveira E, Peace D: Microsur-gical anatomy of the veins of the posterior fossa. J Neurosurg59:63–105, 1983.

26. Mayberg MR, Symon L: Meningiomas of the clivus and apicalpetrous bone: Report of 35 cases. J Neurosurg 65:160–167, 1986.

27. McElveen JT: The translabyrinthine approach to the cerebel-lopontine angle tumors, in Wilkins RH, Rengachary SS (eds):Neurosurgery Update I: Diagnosis, Operative Technique, and Neuro-oncology. New York, McGraw-Hill, 1990, pp 415–423.

28. Morrison AW, King TT: Experiences with a translabyrinthine-transtentorial approach to the cerebellopontine angle. J Neuro-surg 38:382–390, 1973.

29. Pait TG, Harris FS, Paullus WS, Rhoton AL Jr: Microsurgicalanatomy and dissection of the temporal bone. Surg Neurol 8:363–391, 1977.

30. Paullus WS, Pait TG, Rhoton AL Jr: Microsurgical exposure of thepetrous portion of the carotid artery. J Neurosurg 47:713–726, 1977.

31. Rhoton AL Jr, Pulec JL, Hall GM, Boyd AS Jr: Absence of boneover the geniculate ganglion. J Neurosurg 28:48–53, 1968.

32. Samii M, Ammirati M, Mahran A, Bini W, Sepehrnia A: Surgeryof petroclival meningiomas: Report of 24 cases. Neurosurgery24:12–17, 1989.

33. Schramm VL Jr: Infratemporal fossa surgery, in Sekhar LN,Schramm VL Jr (eds): Tumors of the Cranial Base: Diagnosis andTreatment. Mount Kisco, Futura Pub. Co., 1987, pp 421–437.

34. Sekhar LN, Estonillo R: Transtemporal approach to the skull base:An anatomical study. Neurosurgery 19:799–808, 1986.

35. Sekhar LN, Jannetta PJ: Cerebellopontine angle meningiomas:Microsurgical excision and follow up results. J Neurosurg 60:500–505, 1984.

S264 Rhoton


36. Sekhar LN, Jannetta PJ, Burkhart LE, Janosky JE: Meningiomasinvolving the clivus: A six-year experience with 41 patients. Neuro-surgery 27:764–781, 1990.

37. Sekhar LN, Schessel DA, Bucur SD, Raso JL, Wright DC: Partiallabyrinthectomy petrous apicectomy approach to neoplastic andvascular lesions of the petroclival area. Neurosurgery 44:537–550,1999.

38. Sekhar LN, Schramm VL Jr, Jones NF: Operative management oflarge neoplasms of the lateral and posterior cranial base, inSekhar LN, Schramm VL Jr (eds): Tumors of the Cranial Base:Diagnosis and Treatment. Mount Kisco, Futura Publishing Co, 1987,pp 655–682.

39. Sekhar LN, Schramm VL Jr, Jones NF: Subtemporal-preauricularinfratemporal fossa approach to large lateral and posterior cranialbase neoplasms. J Neurosurg 67:488–499, 1987.

40. Sekhar LN, Schramm VL Jr, Jones NF, Yonas H, Horton J,Latchaw RE, Curtain H: Operative exposure and management ofthe petrous and upper cervical internal carotid artery. Neuro-surgery 19:967–982, 1986.

41. Sen CN, Sekhar LN: The subtemporal and preauricular infratem-poral approach to intradural structures ventral to the brain stem.J Neurosurg 73:345–354, 1990.

42. Shiobara R, Ohira T, Kanzaki J, Toya S: A modified extendedmiddle cranial fossa approach for acoustic nerve tumors. J Neuro-surg 68:358–365, 1988.

43. Tator CH, Nedzelski JM: Facial nerve preservation in patients withlarge acoustic neuromas treated by a combined middle fossatranstentorial translabyrinthine approach. J Neurosurg 57:1–7, 1982.

44. Tedeschi H, Rhoton AL Jr: Lateral approaches to the petroclivalregion. Surg Neurol 41:180–216, 1994.

45. Wen HT, Rhoton AL Jr, Katsuta T, de Oliveira E: Microsurgicalanatomy of the transcondylar, supracondylar, and paracondylarextensions of the far-lateral approach. J Neurosurg 87:555–585,1997.

46. Yasargil MG, Mortara RW, Curcic M: Meningiomas of basal pos-terior cranial fossa, in Krayenbuhl H (ed): Advances and TechnicalStandards in Neurosurgery. Wien, Springer-Verlag, 1980, vol 17, pp3–115.

Anatomy of the human ear, a drawing by Max Brodel using Wolff’s carbon pencil and dust on Ross stippleboard.Courtesy, W.B. Saunders Co. (Also see pages S210 and S266.)

Temporal Bone S265
