Surgical treatment of complex intracranial aneurysms: Commentary

SURGICAL TREATMENT OF COMPLEXINTRACRANIAL ANEURYSMS

COMPLEX INTRACRANIAL ANEURYSMS include not only giant aneurysms (classicallylarger than 25 mm in diameter) but also smaller aneurysms in difficult locations of thehuman brain and cranial base. Such lesions are associated with a high risk of subarach-noid hemorrhage and progressive neurological deterioration or death caused by masseffect or stroke. In the past 30 years, the understanding and treatment of these lesionshave progressed considerably. Nonetheless, a deep understanding of these lesions,including the nuances of blood flow dynamics, natural history, and potential therapeu-tic options, is necessary when one is managing such aneurysms. The senior author’s(RFS) clinical experience with more than 5000 brain aneurysms was reviewed. We alsoreviewed recent literature on the surgical management of giant cerebral aneurysms,focusing on the most up-to-date microsurgical techniques. Combinations of therapiescan be used in an attempt to provide a solution to various clinical dilemmas associ-ated with the management of these difficult lesions. The synergistic association betweenmicrosurgery and endovascular modalities is also illustrated. On the basis of the knowl-edge obtained over the years, indirect and multimodality approaches are becomingmore common as neurosurgeons strive to improve patient outcomes.

KEY WORDS: Cerebral revascularization, Complex aneurysm, Giant aneurysm, Microneurosurgery

Neurosurgery [SHC Suppl 3]:SHC1289–SHC1299, 2008 DOI: 10.1227/01.NEU.0000318092.86562.F

NEUROSURGERY VOLUME 62 | NUMBER 6 | JUNE 2008 SUPPLEMENT | SHC1289

GIANT ANEURYSMS

Ricardo A. Hanel, M.D., Ph.D.Department of Neurosurgery,Mayo Clinic,Jacksonville, Florida

Robert F. Spetzler, M.D.Division of Neurological Surgery,Barrow Neurological Institute,St. Joseph’s Hospital and Medical Center,Phoenix, Arizona

Reprint requests:Robert F. Spetzler, M.D.,c/o Neuroscience Publications,Barrow Neurological Institute,350 West Thomas Road,Phoenix, AZ 85013.Email: [email protected]

Received, December 18, 2007.

Accepted, March 31, 2008.

Giant and complex intracranial aneurysms are amongthe most challenging lesions faced by neurosurgeons.The poor natural history of these lesions is related to

their mass effect on the surrounding brain tissue, to embolithat can dislodge to downstream vascular territory, and to theirhigh risk for rupture compared with that of other aneurysms.The complexity of these lesions usually makes their treatmentmore difficult, and they are associated with a high incidence ofcomplications. Consequently, considerable expertise is requiredto manage such lesions.

Detailed preoperative planning includes magnetic resonanceimaging (MRI), computed tomographic angiography (CTA),and catheter-based angiography. Balloon test occlusion of theparent vessel can often provide additional valuable informationfor surgical planning. The treatment of complex aneurysmsshould be based on a balance between the risks associated witheach treatment and its benefit to the patient.

Although preoperative planning serves as a guide for eachprocedure, surgeons must be prepared to respond to clinicalscenarios as they arise. Depending on intraoperative findings,procedures often begin with the options of direct clipping,wrapping, and potential bypass. Thus, surgeons should befamiliar with all aspects of cerebrovascular surgery, includingcranial base approaches for ideal exposure, proximal and dis-

tal control, advanced clipping and wrapping skills, and bypassand microsuturing techniques.

We reviewed the senior author’s (RFS) experience with com-plex intracranial aneurysms obtained from more than 5000treated aneurysms. Strategies for treating these lesions areemphasized, including the decision to treat, preoperative plan-ning, use of cranial base approaches, and surgical techniques.

DEFINITION

Classically, giant intracranial aneurysms are defined aslesions with a diameter of greater than 25 mm (15). Many otherfeatures also play a critical role in defining the complexity of ananeurysm: its location, previous treatments, and the presenceor absence of collateral circulation, intraluminal thrombus, andcalcification of the aneurysmal wall. Similar technical chal-lenges are found with some lesions smaller than 25 mm, whichare termed complex intracranial aneurysms. The same princi-ples of treatment are applicable to both giant and complexintracranial aneurysms.

The biological nature and behavior of saccular and fusiformaneurysms probably differ from those of complex aneurysms.For the sake of simplicity, however, we consider both in the dis-cussion of the general principles that follows.

ONLINEDIGITAL

VIDEO

EPIDEMIOLOGY

Only about 5% of intracranial aneurysms are giant (1, 9, 23).A significantly greater proportion of giant aneurysms occur inthe pediatric population (5). Typically, these lesions involvesegments of the internal carotid artery (ICA), especially thecavernous and paraclinoid segments, followed by the verte-brobasilar region. The remainder involve primarily the middlecerebral artery (MCA) and anterior cerebral artery (1, 5).

Morphologically, giant aneurysms are typically divided intosaccular and fusiform types. Fusiform aneurysms tend to arisein the territories of the vertebrobasilar arteries and MCAs. Themost common clinical presentations are subarachnoid hemor-rhage, intracerebral hemorrhage, or both (1, 9, 17). Other man-ifestations include mass effect, occlusion of perforating vessels,distal embolic events, and seizures. Occasionally, asymptomaticlesions are found incidentally on noninvasive imaging.

NATURAL HISTORY

The natural history of untreated giant cerebral aneurysms isremarkably poor. In the International Study for UnrupturedIntracranial Aneurysms, Wiebers et al. (25) reported that the 5-year incidence of rupture was 40% for anterior and 50% forposterior circulation giant aneurysms or 8 to 10% per year. Inthe series of Peerless et al. (18), the mortality rate of patientswho did not present with hemorrhage was higher than 60%within 2 years, and all surviving patients had marked neuro-logical disabilities. The prognosis was even worse for patientswho became symptomatic with subarachnoid hemorrhage.

TREATMENT PLANNING

Treatment of giant and complex aneurysms requires carefulplanning, with meticulous acquisition and review of allneeded information before treatment. The choice of therapeu-tic modality and approach is based on this information.Different imaging modalities can add important information.Computed tomographic scanning is best for the evaluation ofcalcification. MRI is ideal for evaluation of the presence ofintraluminal thrombus, perilesional edema, and possible asso-ciated infarcts. Both CTA and magnetic resonance angiogra-phy allow three-dimensional reconstruction of the lesion andits surroundings to facilitate preoperative visualization of sur-gical challenges. After clipping procedures, CTA is the nonin-vasive method of choice for evaluating residual or recurrentaneurysms. Magnetic resonance angiography is best for eval-uating aneurysms in need of coiling.

Although used less frequently for cerebral aneurysms in gen-eral, catheter-based angiography is often used to evaluate com-plex giant aneurysms as recent improvements in noninvasiveimages modalities (i.e., CTA and magnetic resonance angiogra-phy) have become available. This option can provide valuableinformation about the direction of blood flow and the possibil-ity of assessing collateral flow to a given vascular territory.Rotational catheter-based angiography with three-dimensional

reconstruction provides the most accurate evaluation of theaneurysmal neck and is important for treatment planning.

Balloon Test Occlusion and the Allcock TestMuch refined since its introduction by Matas (16) in 1911,

temporary carotid occlusion offers valuable information duringpreoperative planning for complex aneurysms. With knownlimitations regarding its predictive value, temporary occlusionof a major cranial vessel allows surgeons to assess the viabilityof collateral flow and, occasionally, to improve their under-standing of the anatomy of the lesion. For example, during thetreatment of giant cavernous aneurysms, the results of tempo-rary occlusion can indicate the type of flow replacementneeded. If balloon occlusion is tolerated, no replacement or,more often, a superficial temporal artery (STA)-to-MCA bypassis indicated. If, however, temporary occlusion evokes neurolog-ical deficits, a high-caliber conduit is needed to replace targetvessel flow.

The use of Allcock’s test (Patient 2) allows surgeons to assessthe patency and caliber of the posterior communicating arter-ies, information that is especially important when aneurysms ofthe basilar artery are treated (3, 19). Balloon test occlusion wasoriginally described as angiographic injection of the vertebralartery simultaneously with unilateral compression of thecarotid artery. However, improved catheter and balloon tech-nology now allows variations in which the basilar artery prox-imal to the aneurysm can be temporarily occluded safely tosimulate sacrifice of the basilar artery.

TREATMENT

General ConsiderationsThe goal of treatment of giant intracranial aneurysms is to

exclude the lesion from the circulation while preserving func-tion in the neural tissues fed by the parent vessel. A multidis-ciplinary approach that includes both surgical and endovascu-lar expertise is often needed to manage such complex lesions.

To discuss the options for endoluminal treatment and recon-struction for giant and complex intracranial aneurysms isbeyond the scope of this article. However, they should be con-sidered when treatment is planned. Advances in endovasculartechnology such as modified stents (covered, partially covered,or low porosity) and new embolic agents will probablyimprove therapeutic options for these complex lesions.

Combined morbidity and mortality rates for the surgicaltreatment of unruptured giant aneurysms (including cognitivedysfunction) vary between 20 and 45%, depending on the loca-tion of the aneurysm and the patient’s age. Older patients andpatients with posterior circulation lesions tend to have thepoorest outcomes (25). Contemporary rates of surgical mortal-ity for treated giant aneurysms, whether ruptured and unrup-tured, vary from 6 to 22% (6, 12, 20). Good or excellent out-comes have been reported in 61 to 87% of patients (6, 12, 20).Patients who become symptomatic with subarachnoid hemor-rhage and mass effect have the worst surgical outcomes (12).

SHC1290 | VOLUME 62 | NUMBER 6 | JUNE 2008 SUPPLEMENT www.neurosurgery-online.com

HANEL AND SPETZLER

Patients harboring giant aneurysms tend to be older thanthose with smaller aneurysms (5). They also tend to havemultiple medical comorbid conditions and a higher risk forcomplications associated with general anesthesia. Comparedwith less complex lesions, giant aneurysms have a higherrate of arterial wall calcifications, atherosclerotic plaque, andintraluminal thrombus. These features complicate direct clipreconstruction. Occasionally, adjunctive treatment techniques,including profound hypothermia and circulatory arrestand flow redirection with or without flow augmentation/replacement, are necessary. Each adjunct incurs an independ-ent risk for complications.

At our center, the decision making process for treating theselesions is individually tailored in each patient. All of the abovefactors are considered and weighed against the risks associ-ated with each potential intervention. Depending on the strat-egy needed to secure an aneurysm, the surgical morbidity andmortality rates for these patients vary tremendously, from 10 to15% for direct clipping and an in situ graft as needed toapproximately 30% when circulatory arrest and hypoperfusionare recommended.

Cerebral Protection and Intraoperative MonitoringFor many years at this institution, barbiturate-induced elec-

troencephalographic burst suppression has been routine duringthe treatment of intracranial aneurysms. These agents are mosteffective when administered before periods of ischemia. Theyreduce cerebral blood volume and metabolism, which helpsprotect the brain. During periods of circulatory arrest, mildhypertension is also used to maximize collateral blood flow.Somatosensory evoked potentials and motor evoked potentialsare recorded in all vascular procedures; additional monitoringis used on the basis of the anatomic area being manipulated.

Surgical TechniqueFundamental principles of aneurysm surgery are especially

important when one is treating the most challenging aneu-rysms. Obtaining proximal and distal vascular control, sharpdissection, meticulous preservation of perforators, circumferen-tial dissection of the aneurysm, and the surgical exposure thatminimizes neural damage is far more difficult to achieve withgiant aneurysms, which often have a calcified neck and intra-luminal thrombus.

Surgical ExposureThe use of cranial base approaches (Fig. 1) to enhance expo-

sures and to minimize damage to and retraction of neural tis-sue has been standard for 15 years. Many articles from thisinstitution have addressed the application and value of suchapproaches for common locations involving giant aneurysms(Table 1) (4, 7, 8, 11–14, 22).

For lesions involving the anterior circulation, we routinelyuse the orbitozygomatic (OZ) craniotomy and its variants(mini-modified, modified, or full OZ) (Fig. 2) tailored to theamount of exposure necessary for a given lesion. For lesionsinvolving the posterior circulation, one or a combination of thefollowing approaches is used (Fig. 3): OZ craniotomy and itsvariants, the transpetrosal approach (Fig. 4), and the far-lateralapproach. When necessary, additional dissection with removalof the posterior clinoid and clivus (i.e., the transcavernousapproach) can be used to enhance exposure of the proximalbasilar artery (2, 4).

Proximal and Distal Vascular ControlProximal and distal vascular control is a basic principle of

aneurysm surgery that is especially important when complexlesions are treated. The aneurysmal wall of giant lesions is oftenthick, atherosclerotic, and relatively unlikely to rupture intraop-eratively. Nonetheless, the size of the body of the aneurysm


SURGICAL TREATMENT OF COMPLEX INTRACRANIAL ANEURYSMS

TABLE 1. Selection of surgical approach based on location ofcomplex aneurysma

Cranial base approach Location

OZ craniotomy tailored Supraclinoid ICA, ICA to lesion (mini-modified, bifurcation, proximalmodified, or full OZ) ACA, MCA

OZ, interhemispheric Distal ACA

OZ Basilar artery apex, SCA

Far lateral Vertebral artery

Far lateral, suboccipital PICA

Far lateral, petrosal VB junction

OZ, petrosal or far lateral AICA, midbasilar trunk

a OZ, orbitozygomatic; ICA, internal carotid artery; ACA, anterior cerebral artery;MCA, middle cerebral artery; SCA, superior cerebellar artery; PICA, posterior inferiorcerebellar artery; VB, vertebrobasilar; AICA, anterior inferior cerebellar artery.

FIGURE 1. Cranial base approaches (shaded areas)for giant aneurysms. The appropriate approach can pro-vide access to almost all vascular lesions. Courtesy ofBarrow Neurological Institute.

itself precludes visualization of the circumference of the lesion,preventing appropriate circumferential dissection. When vas-cular control is achieved, the surgeon can arrest blood flow tothe lesion and proceed with one of several maneuvers, such assuction decompression, opening and resection of the aneurys-mal contents, and endarterectomy of the aneurysmal wall.

For aneurysms of the ICA, such as ophthalmic and otheraneurysms of the paraclinoid region, proximal control can beobtained by exposing the cervical carotid artery. Other options,such as exposure of the petrous carotid artery via Glasscock’striangle, exposure of the clinoid segment with an anterior cli-noidectomy, and endoluminal occlusion with balloons at differ-ent levels, including at the neck of the aneurysm, have beendescribed (13, 24). For lesions of the anterior cerebral arteriesand MCAs, proximal control can often be obtained withoutdifficulty. Exposure of a proximal segment of vessel to enablevascular control of lesions of the posterior circulation is farmore difficult to obtain. For these lesions, maximal surgicalexposure is essential to obtain successful vascular control.

Hypothermic circulatory arrest offers the ultimate in vascu-lar control. The indications for this technique are decreasing asadvances are made in bypass techniques and endovascularneurosurgery. Nonetheless, circulatory arrest permits the sur-geon to work in a bloodless surgical field with no risk ofaneurysmal rupture. The aneurysmal wall can be collapsed togain a crucial few millimeters of exposure. Relaxation of theaneurysm also allows dissection and preservation of the perfo-rating arteries.

Ponce et al. (unpublished data) recently summarized the sen-ior author ’s (RFS) experience with this technique. Theseauthors retrospectively reviewed 105 patients (65 women and40 men; mean age, 44.8 yr) who underwent 107 deep hypother-mic circulatory arrest procedures between 1985 and 2005. Of 97posterior circulation aneurysms, 60 involved the basilar apex.Seven patients harbored anterior circulation aneurysms. Theperioperative mortality rate was 13.3% (14 patients). Follow-upwas available from 84 of the 91 patients discharged after theprocedure (92.3%). Of these, 65 patients were the same or bet-ter after surgical intervention (77% of those who survived), 10patients were worse, and nine patients had died. The meanpostoperative Glasgow Outcome Scale score was 4. If the peri-operatively deceased group is analyzed with the patients avail-able for follow-up, the combined morbidity and mortality ratewas 33%. However, the cause of death for the nine patientsdeceased at the time of follow-up cannot be known precisely,and these patients could skew the data. An encouraging resultwas that at the time of follow-up the annual hemorrhage rateafter microsurgical clipping under cardiac standstill was 0.5%per year, and 92% of the patients had required no further treat-ment of their aneurysm.

These data demonstrate that deep hypothermic circulatoryarrest remains an important treatment for complex and giantposterior circulation aneurysms. When compared with the nat-ural history of these aneurysms, the risks associated with car-diac standstill are acceptable. Given the relatively high morbid-ity and mortality rates associated with this technique, it is


HANEL AND SPETZLER

FIGURE 3. Illustration of selected approach for eacharea of the vertebrobasilar system, which can be dividedinto five segments. The upper two-fifths of the basilarartery can be accessed via an OZ craniotomy, the mid-dle fifth via a petrosal approach, and the lower two-fifths via a far-lateral craniotomy. Courtesy of BarrowNeurological Institute.

FIGURE 4. Variants of the transpetrosal approach toaccess aneurysms of the posterior circulation. Courtesyof Barrow Neurological Institute.

FIGURE 2. Comparison of pterional (A) and orbitozygomatic (OZ) (B)craniotomies. The OZ craniotomy increases the angle of attack and min-imizes brain retraction. Courtesy of Barrow Neurological Institute.

A B

reserved for highly selected patients for whom all other surgi-cal and endovascular options have been exhausted.

Tactics for Aneurysm RepairMany strategies can be used to repair aneurysms. The selection

of the optimal technique for any given lesion is the essence ofmaximizing outcomes. Direct exposure of the aneurysm and clipreconstruction of the parent vessel is the most common strategy.Variations include clip-wrapping or wrapping only. When thedirect approach is infeasible or judged to have an exceedinglyhigh risk, alternative approaches can be used (13). Primary prox-imal vessel occlusion (Hunterian ligation), distal vessel occlu-sion, and trapping with or without flow replacement (bypass) areoften common options. When the anatomy permits, aneurysmscan be excised with or without an interposition graft to reestab-lish blood flow. Aneurysmorrhaphy can also be applied.

Intraoperative ImagingTo minimize complications, many different modalities have

been used intraoperatively to assess the results of aneurysmalrepair and preservation of the parent vessel. Traditionally, intra-

operative ultrasonography and routine intraoperative cerebralangiography have been used (10). More recently, the advent ofindocyanine green (ICG) videoangiography (21) has allowedsurgeons to assess the same parameters with this less-invasivemethod. ICG videoangiography consists of an intravenous injec-tion of a fluorescent dye (ICG) that can be visualized throughthe vessel wall on the areas exposed to light from a surgicalmicroscope. A special infrared filter allows the fluorescent dyein the vessel lumen to be recorded. This method has allowed usto reduce the use of intraoperative angiography to about 20% ofthe aneurysms operated on (RF Spetzler, unpublished data).Angiography is reserved for patients in whom ICG videoan-giography does not clarify the presence of stenosis or occlusionin the parent vessel or filling of residual aneurysm because theparent vessel cannot be visualized or because of heavy calcifica-tion or atheromatous plaque in the vessel.

The main goal of this article is to illustrate the principles dis-cussed above that are well known to many vascular and gen-eral neurosurgeons through selected videos, which provide alive demonstration of many of these strategies and direct appli-cation on a case-by-case basis.



FIGURE 5. Giant aneurysm of the midbasilar trunk treated via a transpet-rosal approach with direct clipping under hypothermic circulatory arrest(see text for description). A, C–H, courtesy of Barrow NeurologicalInstitute, Phoenix, Arizona. B, from, Bambakadis NC, Gonzalez LF, Amin-

Hanjani S, Deshmukh VR, Porter RW, Daspit PC, Spetzler RF: Combinedskull base approaches to the posterior fossa. Technical note. NeurosurgFocus 19:E8, 2005.

A

E F G

B

H

C D

ILLUSTRATIVE CASES

Patient 1: Direct Clipping UnderCirculatory Arrest

(see video at web site)A 51-year-old man presented with complaints of headache and dou-

ble vision. Computed tomographic scans (Fig. 5A) and MRI (Fig. 5B)scans showed the presence of a large aneurysm with significant brain-

stem compression. CTA (Fig. 5C) and diagnostic cerebral angiography(Fig. 5, D and E) confirmed the presence of a giant saccular aneurysmof the basilar artery just above the origin of the anterior inferior cere-bellar arteries.

Given the location of the lesion at midclivus, a decision was made touse a right-sided transpetrosal approach. Because the size of theaneurysm would probably preclude vascular control, hypothermic cir-culatory arrest was used. The parent vessel was reconstructed by directclipping (Fig. 5, F–H).

Learning PointsArrest of blood flow to an aneurysm through temporary occlusion of

the proximal vessel, temporary proximal and distal occlusion, or circu-latory arrest allows an aneurysm to relax and provides the surgeon theopportunity to complete circumferential dissection of the aneurysmwhile preserving adjacent neurovascular structures.

When formulating a clipping strategy, surgeons should consider thepossibility that occlusion with a single large clip may be ineffectivebecause the closing force at the tip of the clip is low. Placing clips inseries takes advantage of the relatively high closing forces of smallerclips and increases surgeons’ freedom to design the reconstruction ofthe parent vessel.

Ideally, as illustrated in this patient, the clip or clips should beapplied parallel to the direction of blood flow. The use of a fenestratedclip allows manipulation of the aneurysm sac through the open area ofthe clip. Additional clips can be used to close the remaining neck at thearea of the fenestration.

Patient 2: Parent Vessel Occlusion

(see video at web site)An 11-year-old boy presented with progressive headaches but no

neurological deficits. Computed tomographic scanning of the head(Fig. 6A) showed a 25-mm, partially thrombosed aneurysm of the basi-lar apex. Conventional angiography (Fig. 6B) and CTA (Fig. 6C) showeda lesion with a broad base, involving the origin of both superior cere-


HANEL AND SPETZLER

G

F

E

D

B

FIGURE 6. Giant aneurysm of the partially thrombosed basilar apextreated via an OZ craniotomy, posterior clinoid drilling, and sacrifice of thebasilar artery (see text for description). Courtesy of Barrow NeurologicalInstitute.

A

C

FIGURE 7. Giant aneurysm of theleft cavernous internal carotidartery (ICA) treated with a left cer-vical ICA-to-middle cerebral artery(MCA) radial graft bypass andproximal occlusion of the carotidartery (see text for description).Courtesy of Barrow NeurologicalInstitute.

BA

C

bellar arteries. Allcock’s test variant with temporary occlusion of thebasilar artery and injections of the right (Fig. 6D) and left ICA (Fig. 6E)showed a patent posterior communicating artery on the right side.

The decision was made to approach the lesion for possible directclipping under hypothermic circulatory arrest rather than sacrificingthe proximal basilar artery. On the basis of the contralateral posterior

communicating artery, a left OZ approach was chosen. Proximal vas-cular control required drilling the posterior clinoid process. Once theaneurysm was exposed, the parent vessel was sacrificed by placing aclip proximal to the origin of the superior cerebellar arteries.Postoperative angiography (Fig. 6F) performed 24 hours after sur-gery showed changes in blood flow that lead to aneurysmal thrombo-sis. There was no blood flow inside the aneurysm (arrow at origin ofposterior cerebral artery). After basilar artery sacrifice, blood flow onthe apex of the basilar artery up to the origin of the SCAs was redi-rected and was no longer directed by the basilar artery into theaneurysm. The flow in the proximal basilar artery via the vertebralartery was good (Fig. 6G), with the aneurysm clip occluding the ves-sel (arrow).

Learning PointsAs illustrated in the video, the transcavernous dissection can be tai-

lored to the exposure needed in each patient. In this patient, only theposterior clinoid needed to be drilled to expose the basilar artery prox-imal to the aneurysm.

Although direct clipping of the aneurysm under hypothermic car-diac arrest was an option for this patient, many features led to thedecision to sacrifice the basilar artery instead. Good collateral bloodflow to the basilar apex via the right posterior communicating artery,involvement of the aneurysm with one superior cerebellar artery, andthe effectiveness of sacrificing the basilar artery guided the intraoper-ative decision.

The change in blood flow through the aneurysm induced by proxi-mal or distal occlusion or both can be applied effectively in many dif-ferent situations, in association with flow replacement, if necessary. Inthese complex cases, the vertebral and basilar arteries can also be sac-rificed (19).

Patient 3: Parent Vessel Occlusionwith Radial Artery Bypass

A 61-year-old woman presented with complete left ophthalmople-gia. Cerebral angiography showed bilateral giant aneurysms of thecavernous ICA (Fig. 7, A and B). Given the symptomatic nature of thelesion, a decision was made to treat the left-sided aneurysm first. A leftOZ craniotomy was performed with a cervical ICA-to-MCA bypassand occlusion of the ICA proximal to the aneurysm (Fig. 7C).

Learning PointsWhether cerebral bypass is or is not associated with parent vessel

occlusion, this technique is an appealing option for treating giantaneurysms in many locations. Revascularization, which has tradition-ally been used when the collateral circulation was judged insufficientafter test occlusion, can be used when collateral blood flow is present.In fact, in some patients, the change in blood flow induced by the graftcan lead to thrombosis of the aneurysm. In the present patient, weselected the cervical ICA as the proximal site of anastomosis. A shorterinterposition graft can be used, and the ICA can be occluded proximalto the aneurysm.

Patient 4: Aneurysm Excision with Figure-eightAnastomosis of M2 to Two Separate M3 Branches Plusan STA-to-M3 End-to-end Anastomosis

(see video at web site)A 39-year-old man presented with memory loss, occasional trouble

finding words, and unremarkable results for a neurological examina-



FIGURE 8. Giant aneurysm of theleft M2 resected via a left OZ cra-niotomy by direct anastomosis ofM2 and two M3 branches (figure-eight and superficial temporalartery (STA)-to-M3 anastomosis) (see text for description). Courtesy ofBarrow Neurological Institute.

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A B

C

D

EF

tion. MRI of the head (Fig. 8A) showed a giant partially thrombosedaneurysm of the left MCA. Conventional angiography showed an M2aneurysm (Fig. 8, B and C). A left OZ craniotomy was performed toexplore the aneurysm. During dissection, two large branches werefound arising from the aneurysm, one of which was a short trunk, nextto a bifurcation point. Proximal and distal vascular control wasobtained. The aneurysm was dissected circumferentially and removed.While one of the distal branches was being prepared for anastomosis,the short trunk was resected. Two individual branches were then leftfor anastomosis to the proximal M2. A figure-eight anastomosis wasused (Fig. 8D) to join these two branches to the proximal M2. The STAwas used to revascularize the other M3 branch. Postoperative angiog-raphy confirmed patency of the figure-eight anastomosis between M2and two separate M3 branches (Fig. 8, E and F; arrows, anastomosissite) as well as patency of the STA-to-M3 anastomosis (Fig. 8G).

Learning PointsDepending on the local anatomy, an aneurysm can be resected via a

primary in situ end-to-end anastomosis. A short arterial graft interpo-sition can also be used. When the craniotomy is performed, preserva-tion of the STA, which can serve as a versatile donor for grafting,should always be attempted. When treating such challenging lesions,

surgeons should be ready to create solutions for potential misadven-tures during surgery.

Patient 5: Combined Microsurgical and EndovascularApproach with a Double-barrel STA-to-MCA BypassPlus Endovascular Aneurysm Occlusion

(see video at web site)A 51-year-old man presented with a transitory loss of speech. The

differential diagnoses were seizure and a transient ischemic attack.Results of MRI of the brain were unremarkable for ischemic lesions.However, a large mass in the left sylvian fissure, highly suggestive ofa giant partially thrombosed MCA aneurysm (Fig. 9A), was seen. CTA(Fig. 9, B and C), conventional angiography (Fig. 9D), and a three-dimensional angiographic reconstruction (Fig. 9E) showed a giant par-tially thrombosed aneurysm with a serpiginous vascular channel as theresidual lumen of the aneurysm. A left OZ craniotomy was performedwith the intention of performing a double-barrel STA bypass into bothbranches of the left MCA distal to the aneurysm followed by partialclip occlusion of the MCA branches distal to the aneurysm (Fig. 9F).Postoperatively, the patient had a new episode of speech loss thatresponded to elevating his blood pressure with vasoactive drugs.


HANEL AND SPETZLER

FIGURE 9. Giant partially thrombosed aneurysm of the left MCA treated viaa left OZ craniotomy, double-barrel STA-to-MCA bypass, partial distal occlu-sion of the parent vessel, and complete coil occlusion of the aneurysm (see textfor description). Courtesy of Barrow Neurological Institute.

A B C D

E

F G H

I J

Angiography showed residual flow in the serpiginous channel of theleft MCA. Temporary balloon occlusion (Fig. 9G) dramaticallyincreased blood flow in the bypass (Fig. 9H). A decision was made toproceed with coil occlusion of the residual aneurysm lumen (Fig. 9I).Computed tomographic perfusion after coil occlusion of the left MCAshowed no evidence of hypoperfusion (Fig. 9J).

Learning PointsAgain, this patient illustrates the utility of the STA for cerebral revas-

cularization in patients with giant aneurysms. A double-barrel graft,divided to each branch of the MCA distal to the aneurysm, was used toincrease blood flow. To reduce the risk of a postoperative ischemic event,we decided to occlude the MCA branches distal to the aneurysm onlypartially. This maneuver decreased the demand on the bypass becausethe patient’s symptoms resolved when perfusion was augmented.Endovascular coil occlusion of the residual conduit lumen createddemand for the bypass, improving perfusion and resolving the patient’ssymptoms. This aneurysm nicely illustrates the synergy betweenmicroneurosurgery and endovascular neurosurgery as complementarymethods. A wise combination of available therapeutic modalitiesimproves overall outcomes for this patient population. Although currentendoluminal treatment for giant intracranial aneurysms has several lim-itations, it can be considered as an initial therapeutic modality or in asso-ciation with microsurgery on a case-by-case basis.

CONCLUSION

The use of microneurosurgical techniques in the treatment ofcomplex intracranial aneurysms continues to be crucial to suc-cessful outcomes. A team approach that includes both micro-surgical and endovascular techniques should be used to opti-mize treatment for patients on a case-by-case basis to ensurethe best possible outcomes for this challenging population. Theevolution of techniques and technology and their judicious usein both microsurgery and endovascular neurosurgery are keyto improving the results of treating these lesions.

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10. Klopfenstein JD, Spetzler RF, Kim LJ, Feiz-Erfan I, Han PP, Zabramski JM,Porter RW, Albuquerque FC, McDougall CG, Fiorella DJ: Comparison of rou-tine and selective use of intraoperative angiography during aneurysm sur-gery: A prospective assessment. J Neurosurg 100:230–235, 2004.

11. Lawton MT, Daspit CP, Spetzler RF: Technical aspects and recent trends in themanagement of large and giant midbasilar artery aneurysms. Neurosurgery41:513–521, 1997.

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22. Spetzler RF, Riina HA, Lemole GM Jr: Giant aneurysms. Neurosurgery49:902–908, 2001.

23. Sundt TM Jr, Piepgras DG, Fode NC, Meyer FB: Giant intracranial aneurysms.Clin Neurosurg 37:116–154, 1991.

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COMMENTS

Giant aneurysms have always been a formidable challenge for vas-cular neurosurgeons. The field continues to evolve, and the drive

for direct neck clipping in every case has been softened by the adoptionof alternative approaches. In this report, Dr. Spetzler focuses on thearray of options available to treat complex and giant aneurysms asdemonstrated by his extensive experience.

Returning to the days of Hunterian ligation, proximal occlusion, ortrapping, with or without bypass, has been applied more liberally inrecent years. Even with cardiac standstill techniques, some giantaneurysms, especially at the basilar apex and at the MCA trifurcation,cannot be safely clipped. The presence of perforators or involvedbranches often limits our ability to perform safe clip reconstructions. Asshown in Illustrative Case 2, proximal basilar occlusion is probablythe best approach for true giant basilar apex aneurysms. With directclipping, even under ideal circumstances, sparing the thalamoperfo-rates is only a 50/50 proposition.



At this time, endovascular options for giant aneurysms are largelylimited to proximal occlusion, often with a preliminary surgical bypassprocedure. Currently approved stent technology cannot usuallyaddress the broad necks of giant aneurysms, and packing coils in giantaneurysms has not been shown to be curative or to improve the natu-ral history of these lesions. However, future stent designs, some alreadyunder investigation, may allow for new methodology of parent vesselreconstruction, providing additional options for treating giantaneurysms.

Robert A. SolomonNew York, New York

The authors have provided a concise yet elegant review of the clini-cal decision making and surgical management of complex intracra-

nial aneurysms, including several highly illustrative case studies. Theserare and difficult lesions require creative management strategies utiliz-ing all of the skills of the cerebrovascular surgeon.

As illustrated by the case studies in this article, the definition of a“complex” aneurysm includes more than large size. Additional fea-tures, such as neck calcification, intraluminal thrombus, complex neckmorphology, and undesirable location, may render an otherwiseinnocuous aneurysm a complex and highly challenging lesion to man-age. Although no definition of “complex aneurysm” is universallyagreed upon, the experienced cerebrovascular surgeon will generallyrecognize the complexity with appropriate preoperative imaging stud-ies. As emphasized by the authors, multiple imaging techniques assistin identifying the complexity of an aneurysm prior to planning andexecuting treatment. Computed tomography to identify calcificationswithin the sac and particularly within the neck is highly valuable indetermining potential intraoperative challenges. Magnetic resonanceimaging will demonstrate associated intraluminal thrombus that maynot be apparent on digital subtraction angiography. Balloon test occlu-sion is useful in determining collateral blood flow and a patient’spotential tolerance of parent vessel sacrifice. Occasionally, the com-plexity of an intracranial aneurysm is not recognized until the lesion isexplored surgically. This fact emphasizes the need for the operatingsurgeon to be flexible and creative in planning and carrying out theoperative procedure. We routinely attempt to preserve the superficialtemporal artery when approaching most brain aneurysms and agreewith the authors that utilizing this very versatile blood supply allowsfor creative, and often unexpected, treatment strategies that evolveduring the surgical procedure.

Optimal management of complex aneurysms requires close collabo-ration among cerebrovascular surgeons and endovascular experts.Despite the shortcomings of endovascular therapy in treating many ofthese complex aneurysms, new advances in endovascular technologyprovide innovative and novel strategies for managing many of theselesions, either alone or combined with surgical treatment.

Despite the rapid advances in endovascular technology, the field ofmicrosurgery has not been static during the past 2 decades. Many ofthe important adjuncts to microsurgical treatment of intracranialaneurysms are illustrated in this article and include cranial base expo-sures; three-dimensional rotational angiography; brain protection,including hypothermic circulatory rest; more liberal use of temporaryclips; modern aneurysm clips with multiple innovative designs, includ-ing fenestrations and multiple angles; use of extracranial-to-intracranialbypass; intraoperative angiography; intraoperative indocyanine greenvideoangiography; and interventional neuroradiology.

As care for patients with complex cases such as these becomesregionalized, neurovascular surgeons and cerebrovascular teams will

be required to collaborate effectively as they are asked to deal withincreasingly complex and challenging lesions.

Alexander MasonDaniel L. BarrowAtlanta, GA

The authors provide us with a review of giant and complexaneurysms. They emphasize the complexity of these lesions and the

demands that they can place on the neurosurgical team. Despite theiruncommon occurrence, the lesions often do require treatment due totheir high risk of rupture. These authors reinforce the value of completeunderstanding of the anatomy of the lesion as defined on computedtomography, magnetic resonance, and digital subtraction angiography.In addition, the value of balloon test occlusion and the Allcock test canprovide further information, which is important in determining thesurgical strategy and whether to incorporate a bypass and what caliberbypass. The authors illustrate cases of direct clip reconstruction, parentvessel occlusion, occlusion and bypass, in situ bypass with end-to-endanastomosis, and combined surgical and endovascular treatment.

At our institution, the neurovascular team assesses giant and com-plex aneurysms. Imaging such as computed tomographic angiogra-phy, magnetic resonance, magnetic resonance angiography, and dig-ital subtraction angiography are routinely performed. In addition,balloon test occlusion is often performed to further assess the conse-quences of vessel sacrifice (deconstructive) procedures, such asHunterian ligation or aneurysm trapping with or without bypass(low-flow vs. high-flow). Given a favorable clinical condition, surgi-cal therapies are favored due to the high recurrence rate from stand-alone endovascular therapy. Often the surgical treatment is combinedwith endovascular strategies during the procedure in order to provideproximal control and soften the aneurysm (suction decompression).Postoperative assessment includes conventional digital subtractionangiography.

These authors have illustrated the demanding and creative strate-gies necessary to treat these complex and giant aneurysms. A strategythat reconstructs the normal vessel lumen is ideal, but not alwaysachievable. When reconstructive strategies are not feasible, decon-structive techniques are deployed with or without flow augmentationto eliminate the aneurysm from the circulation and protect againstthe severe consequences of SAH. In the current era, endovasculartreatment can be combined with open surgical techniques to improvepatient outcome.

Daniel SurdellH. Hunt BatjerChicago, IL

This is a nice piece of work showing the state of the art in the chang-ing world. The pain, but also the happiness of success in treating

these challenging patients, can be seen in the text, between the lines,and in the beautiful videos. The Helsinki and Kuopio Finnish collec-tive’s experience of more than 10,000 patients with cerebral aneurysmstreated is very similar to the one presented here (1). We have selecteddifferently in the following: 1) We have never used extracorporeal cir-culation, despite having done preparatory steps towards it. This mightbe based on the cooperation with the late Dr. Drake, and his negativeexperience in some of the early cases among his total of 900 giantaneurysms treated (2). 2) We never adopted wide use of orbitozygo-matic approaches after an initial trial. We have found useful variationsin the treatment of these difficult cases with the help of different low-and high-flow bypasses, and short-term use of transient cardiac stand-


HANEL AND SPETZLER

still by intravenous administration of Adenosine, and with our simple,fast approaches (3–6, 8).

The current paper shows what a unit at the top of the vascularmicroneurosurgical world can and, in fact, should do. Patients withvascular lesions should be centralized in similar centers of excellencefor better results (7).

Reza DashtiIstanbul, Turkey

Mika NiemeläJuha A. HernesniemiHelsinki, Finland

1. Dashti R, Hernesniemi J, Niemelä M, Rinne J, Porras M, Lehecka M, Shen H,Albayrak BS, Lehto H, Koroknay-Pal P, Sillero R, Perra G, Ronkainen A,Koivisto T, Jääskeläinen JE: Microneurosurgical management of middle cere-bral artery bifurcation aneurysms. Surg Neurol 67:441–456, 2007.

2. Drake CG, Peerless SJ, Hernesniemi JA: Early surgery for ruptured verte-brobasilar aneurysms. J Neurosurg 80:643–649, 1994.

3. Hernesniemi J, Ishii K, Niemelä M, Kivipelto L, Fujiki M, Shen H: Subtemporalapproach to basilar bifurcation aneurysms: advanced technique and clinicalexperience. Acta Neurochir 94 [Suppl]:31–38, 2005.

4. Hernesniemi J, Ishii K, Niemelä M, Smrcka M, Kivipelto L, Fujiki M, Shen H:Lateral supraorbital approach as an alternative to the classical pterionalapproach. Acta Neurochir 94 [Suppl]:17–21, 2005.

5. Hernesniemi J, Niemelä M, Kivipelto L, Ishii K, Rinne J, Ronkainen J, KivisaariR, Shen H, Karatas A, Lehecka M, Frösen J, Piippo A, Jääskeläinen J: Some col-lected principles of microneurosurgery: simple and fast, while preserving nor-mal anatomy: a review. Surg Neurol 64:195–200, 2005.

6. Nagy L, Toth S, Ishii K, Shen H, Karatas A, Vajda J, Niemelä M, JääskeläinenJ, Hernesniemi J: Water dissection technique of Toth for opening neurosurgi-cal cleavage planes. Surg Neurol 65:38–41, 2006.

7. Niemelä M, Koivisto T, Kivipelto L, Ishii K, Rinne J, Ronkainen A, Kivisaari R,Shen H, Karatas A, Lehecka M, Frösen J, Piippo A, Jääskeläinen J, HernesniemiJ: Microsurgical clipping of cerebral aneurysms after the ISAT Study. ActaNeurochir 94 [Suppl]:3–6, 2005.

8. Randell T, Niemelä M, Kyttä J, Tanskanen P, Määttänen M, Karatas A, Ishii K,Dashti R, Hernesniemi J: Principles of neuroanesthesia in aneurysmal sub-arachnoid hemorrhage: The Helsinki experience. Surg Neurol 66:382–388,2006.

This article presents a general overview of the surgical treatment ofcomplex intracranial aneurysms, together with a collection of five

videos that demonstrate the technical skill and ingenuity of the seniorauthor (RFS). A team approach that combines microsurgical andendovascular techniques is evident in these cases. Decreasing indica-tions for hypothermic circulatory arrest, intraoperative angiography,and full orbitozygomatic craniotomy are noteworthy and have beenaccompanied by increasing indications for bypasses, endovascular

techniques, indocyanine green videoangiography, and modifiedorbitozygomatic approaches. Techniques like the “figure-eight anasto-mosis” (Illustrative Case 4) show that even though endovascular ther-apies evolve and expand in their scope, there is always room for morecreative microsurgical solutions for complex aneurysms.

Michael T. LawtonSan Francisco, CA

In this review, Hanel and Spetzler have reviewed the status of surgi-cal treatments for complex brain aneurysms, drawing upon the sen-

ior author’s (RFS) extensive experience, expertise, and innovation inthis area. The treatment of complex and giant aneurysms is continu-ously evolving at present due to the innovation of various endovascu-lar treatment methods. The most recent addition to this armamentar-ium is the “pipeline stent,” which works on the principle of flowdiversion. However, intravascular stents are associated with long-termissues of in-stent stenosis and aneurysm recurrence, and the results ofendovascular techniques are still disappointing with respect to giantaneurysms.

Microsurgery is therefore expected to play a major role in the man-agement of complex aneurysms in the next 5 to 10 years, at least. Thetechniques available for microsurgical management include clip recon-struction of the aneurysm, bypass with aneurysm occlusion or trap-ping, and deep hypothermic circulatory arrest-assisted clipping. Therole of these techniques will depend upon a number of factors, whichinclude the patient’s age and comorbidities, expected natural history ofthe aneurysms, and the individual surgeon’s (or surgical team’s) expe-rience with these techniques, as well as whether the aneurysm is arecently ruptured one. Based on my personal experience and the expe-rience in the UW Aneurysm Treatment Center in recently rupturedaneurysms, I prefer clip reconstruction or balloon-assisted coilingwhenever possible, bypass techniques only when absolutely needed,and intravascular stents only for rescue during endovascular emer-gencies. In unruptured aneurysms, both stent-assisted coiling andbypass-assisted clipping or trapping have a greater role to play. In myview, the role of the deep hypothermic circulatory arrest technique isgreatly diminished nowadays, due to both the unpredictability of theresults, even when the operation goes perfectly well, and the complex-ity of the operation.

The challenge we are faced with now is how to train a future gener-ation of neurosurgeons who can actually perform both these complexoperations and endovascular surgery. Due to the diminished operativeexperience available, the demand for excellent results, and the longtraining time needed, it is more difficult to train vascular surgeons formicrosurgery than for endovascular surgery.

Laligam N. SekharSeattle, WA



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Surgical treatment of complex intracranial aneurysms: Commentary

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