The Journal of
Laryngology and Otology{Founded in 1887 by MORELL MACKENZIE and
NORRIS WOLFENDEN)
July 1964 THE DEVELOPMENT OF THE MIDDLE EAR SPACES AND THEIR
SURGICAL SIGNIFICANCE*By BRUCE PROCTOR (Detroit)
THE recent advances in techniques for surgery of the middle-ear
cleft has revived interest in the microanatomy of the middle ear.
In the present study the previous works of anatomists and
otologists working in this field was intensively reviewed. Fresh
temporal bones were then procured at autopsy and preserved by deep
freezing. Later micro-dissections were made, photographed and then
sketched by a competent medical illustrator. Our attention will be
directed first to the contents of the middle ear, then to the
embryological origin and finally to the surgical significance of
these structures. The middle ear contains the ossicular chain with
its ligaments and the tendons of the tensor tympani and stapedius
muscles. Along with the chorda tympani nerve these structures may
be considered as the "viscera" of the tympanic cavity (Braus,
i960). Attached to the ossicular chain are various mucosal folds
(Ballance and Green, 1919; Hammar, 1902; Maisonnet and Coudane,
1950; Politzer, 1909; Sobotta, 1920; Lowndes Yates, 1936) which are
of considerable clinical importance in that they carry blood
vessels to the ossicles and also divide the middle ear into several
definite compartments. They may* Read at the Section of Otology,
Royal Society of Medicine, London, December 6th 1963-
631
Bruce Proctorbe considered as the "mesenteries" of the tympanic
cavity. These mucosal folds are easily seen in the living and in
fresh temporal bones. They disappear or disintegrate rapidly if the
temporal bones are permitted to dry or are immersed in fixative
solutions. They may also disintegrate in disease processes
involving the middle ear. Mucosal folds and their remnants are
often considered as residues of inflammation or as adhesions. It
must be emphasized, therefore, that they occur in fairly constant
anatomical positions which can be explained by the embryological
development of the middle ear.Compartments and Folds of the Middle
Ear
The attic or epitympanum is almost completely separated from the
mesotympanum by the ossicles and their folds except for two small
but constant openings which it is proposed to call the isthmus
tympani anticus and the isthmus tympani posticus (Plate I). The
anterior opening lies posterior to the tensor tympani tendon and
anterior to the stapes and long crus of the incus. The posterior
opening is bounded posteriorly by the pyramidal process and
posterior tympanic wall, laterally by the short process of the
incus and posterior incudal ligament and anteriorly by the medial
incudal fold which extends from the short to the long process of
the incus. Its medial boundary is the stapes and the stapedial
tendon. The attic usually extends forward through the incisura
tensoris and anterior to the tensor tendon as the anterior
malleolar space or anterior compartment of the attic. This space
lies above the tensor fold which extends laterally from the
semicanal for the tensor tympani muscle to the anterior malleolar
ligament. The attic, however, may extend anteriorly only to the
level of the tensor tendon where it is limited by a medial
extension of the superior malleolar fold instead of by the tensor
fold which in such an instance does not form. The space anteriorly
would be in communication with the mesotympanum and eustachian
tube. This space, when present, is called the supratubal space.
Posterior to the transversely-placed superior malleolar fold lies
the larger posterior compartment of the attic. That portion of this
compartment lateral to the superior incudal fold may be considered
as the superior incudal space and that portion medial to the
superior incudal fold as the medial incudal space. Laterally the
floor of the superior incudal space is formed by the lateral
malleolar fold and by the lateral incudal fold which extends
posteriorly to the posterior incudal ligament. The entrance into
Prussak's space is usually located between the lateral malleolar
fold and the lateral incudal fold. Medially the posterior
compartment of the attic is separated from the mesotympanum by the
dihedral-shaped medial incudal fold which632
The Development of the Middle Ear Spacesextends from both crura
of the incus to the pyramidal eminence and stapes (Plates II and
III). Beneath the floor of the attic and in the upper mesotympanum
there are three compartments. They are the inferior incudal space
and the anterior and posterior pouches of von Troeltsch. The
inferior incudal space extends from the inferior surface of the
incus laterally to the posterior malleolar fold (Plate IV). It is
limited medially by the medial incudal fold and anteriorly by the
interossicular fold which lies between the long crus of the incus
and the upper two-thirds of the malleus handle. Between the
posterior malleolar fold and the tympanic membrane lies the
posterior pouch of von Troeltsch (Plate V). The chorda tympani
nerve lies in the free margin of the posterior malleolar fold,
although it may cross the posterior tympanum independent of this
fold. The shallow anterior pouch of von Troeltsch lies between that
portion of the drumhead anterior to the malleus handle and the
anterior malleolar fold which is draped on the anterior malleolar
ligament. Between the malleus handle and the drumhead and superior
to the umbo lies the shallow manubrial fold. Five folds may be
recognized as stapedial folds (Plate VI). They are the obturatoria
stapedis between the crura, the anterior stapedial fold between
promontory and anterior crus, the posterior stapedial between
promontory and posterior crus, the plica stapedis between pyramidal
eminence and the posterior crus and the superior stapedial folds
which extend from the long crus of the incus to either crus of the
stapes or from the facial canal to the crura.Prussak's Space
The annulus fibrosus, the dense fibrocartilaginous ring to which
the radial fibres of the drum attach, leaves the sulcus tympanicus
posteriorly (Plate VII). Its outer fibres insert on the posterior
tympanic spine or extend in the stria membrana tympani posticus to
the short process of the malleus. Its inner fibres insert on the
medially-placed pretympanic spine (Dworacek, 1960; Pernkopf, i960)
or radiate out, forming the supporting structure for the posterior
malleolar fold and attaching on the posteromedial aspect of the
upper third of the malleus handle. Between the posterior malleolar
fold and the drum lies the posterior pouch of von Troeltsch.
Anteriorly the annulus fibrosus leaves the sulcus tympanicus to
attach in part to the anterior tympanic spine then continues on:
(1) as the stria membrana tympani anticus to the short process, (2)
to radiate out to help form the floor of Prussak's space, (3) to
interdigitate with fibres of the lateral malleolar fold, and (4) to
attach to the bony rim of the notch of Rivinus.633
Bruce ProctorThe lateral malleolar fold arises from the junction
of the malleus head and neck and radiates out to insert on the
entire bony rim of the notch of Rivinus, thus forming a firm roof
for Prussak's space (Plate VIII).The Embryology
Between the third and seventh foetal month the gelatinous tissue
of the middle-ear cleft is gradually absorbed. At the same time the
primitive tympanic cavity develops by a growth, into the cleft, of
an endotheliallined fluid pouch extending from the eustachian tube
(Plate IX). Four primary sacs or pouches then bud out. They are
saccus anticus, saccus medius, saccus superior and saccus posticus
(Hammar, 1902). Where these pouches contact each other mucosal
folds are formed. Between the mucosal layers of the folds are
remnants of the mesoderm, including blood vessels supplying the
"viscera" of the tympanic cavity. Saccus anticus is the smallest of
the pouches. It extends upward anterior to the tensor tendon to
form the anterior pouch of von Troeltsch. Its upward extent may be
limited at the level of the semicanal for the tensor tympani by
contact with the anterior-most saccule derived from the faster
developing saccus medius (Plate X). The fold formed is the tensor
fold and above it is the anterior compartment of the attic. Saccus
anticus may, however, extend upward to the tegmen and as far
posterior as the superior malleolar fold. In this instance there is
developed a supratubal space instead of an anterior attic
compartment (Plate XI). Saccus medius forms the attic. It extends
upward through the isthmus tympani anticus and usually breaks up
into three saccules. The anterior saccule may form the anterior
compartment of the attic. The medial saccule forms the superior
incudal space by growth over the malleoincudal body to the lateral
incudal fold and posterior incudal ligament. The medial saccule
usually sends an offshoot forward between the lateral malleolar and
lateral incudal folds to form Prussak's space. Occasionally the
medial saccule extends only to the level of a superior incudal fold
in which case the lateral incudal fold is absent. The superior
incudal space would in such an instance be developed from the
saccus superior. The posterior saccule of saccus medius extends
posteriorly to the anterior crus of the stapes, passes medial to
the long crus of the incus and eventually pneumatizes that portion
of the mastoid air cell system which is derived from the pars
petrosa of the temporal bone. Saccus superior extends posteriorly
and laterally in the interval between the malleus handle and the
tip of the long crus of the incus. It forms the posterior pouch of
von Troeltsch and the inferior incudal space. Its upper limit is
the lateral incudal fold, although it may extend to the level of a
complete superior incudal fold and also extend into Prussak's
space. Posteriorly saccus superior extends medially to pass over
the pyramidal eminence into the antrum. Eventually it pneumatizes
that634
The Development of the Middle Ear SpacesFor Anatomical Key see
page 647
PLATE I.
Floor of attic viewed from above. The mesotympanum is almost
completely separated from the attic by the ossicular chain and
mucosal folds. The only constant communication are the isthmus
tympani anticus and the isthmus tympani posticus.
635
Bruce Proctor
PLATE II.
The ossicles viewed from posterior, superior and medial. The
medial incudal fold extends medially and postero-inferiorly from
the incus crura to the stapedial tendon.
636
The Development of the Middle Ear Spaces
PLATE
III.
Lateral view of tympanum. Note the anterior compartment of the
attic with the tensor fold as the floor, the interossicular fold
between malleus and incus and the medial incudal fold with the
isthmus tympani posticus behind.
637
Bruce Proctor23
PLATE IV.
Postero-superior and lateral view of middle-ear contents showing
embryological origin. Saccus medius forms the superior incudal
space, Prussak's space and extending posteriorly into the mastoid
(pars petrosa). Saccus superior forms the inferior incudal space,
posterior pouch of von Troeltsch and extending into that portion of
the mastoid developed from pars squamosa. Saccus posticus forms the
round window niche, sinus tympani and lower half of oval window
niche.
638
The Development of the Middle Ear Spaces
PLATE V.
Section of malleus. Anterior aspect (right) and posterior aspect
(left). Note anterior and posterior pouches of von Troeltsch.
639
PLATE VI.
Five combinations of the various stapes folds showing their
embryological origin. 640
The Development of the Middle Ear Spaces
PLATE
VII.
Detail of Prussak's space. Terminal fibres of annulus fibrosus
spread out to help form the boundaries of Prussak's space. The roof
is formed by the lateral malleolar fold which fans out to attach
along the rim of the notch of Rivinus.
641
Bruce Proctor
PLATE VIIT.
Prussak's space. Frontal section showing the posterior
two-thirds of this space. Note the anterior malleolar fold
extending from the anterior process of the malleus to the stria
membrana tympani anticus. 642
The Development of the Middle Ear Spaces
PLATE
IX.
Illustrates growth of pouches into the middle ear of 3- to
7-month-old embryos.
643
Bruce Proctor
18
G.S. L.ASHBROOK
PLATE X.
Development of anterior compartment of the attic by saccus
medius with the saccus anticus stopping at the level of the
semicanal and tensor tympani tendon resulting in formation of the
tensor fold.
644
The Development of the Middle Ear Spaces
PLATE
XI.
Development of the anterior compartment of the attic by
extension of saccus anticus to superior malleolar fold.
645