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Temporal Bone Histology and Radiology Atlas106
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HORIZONTAL SECTION 11
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Temporal Bone Histology and Radiology Atlas108
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Figure 6–40. Note the similarity in width between the normal vestibular aqueduct (VA) and posterior semicircular canal
(PSCC) in this axial temporal bone CT image.
brain. The VA is often identi fied in the radiographic
image at or just below the IAC. The normal width of
the VA at its midpoint is 0.9 mm or smaller, and at its
opercular width is 1.9 mm or smaller.16 A good rule
of thumb on CT and MR imaging is that the diameter
of the VA should be no larger than the diameter of its
neighboring posterior semicircular canal (Figure 6–40).
The cochlear aqueduct (CA) lies in a plane parallel and inferior to the IAC. It provides a potential communication between the subarachnoid space and the
perilymph. Its opening into the cochlea is at the medial
aspect of the basal turn of the cochlea. The average size
of the CA is 2.9 mm.17 The CA is a preformed pathway
for the communication of meningitis to the cochlea.18
6. Horizontal Temporal Bone Sections with Corresponding Computed Tomography Images 109
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Figure 6–41. Endoscopic view of posterior mesotympanum and sinus tympani. st = Sinus tympani, p = ponticulus, su = subicu-
lum, rw = round window, pr = promontory, ps = posterior sinus, ma = malleus, s = stapes, in = incus, pe = pyramidal eminence,
fn = facial nerve. (Reproduced, with permission, from Marchioni D, Molteni G, Presutti L. Indian Journal of Otolaryngology and
Head & Neck Surgery. 2011;63(2):101–113.)
A patent or enlarged CA may predispose to perilymph
“gusher” or leak of cerebrospinal fluid from the stapes
opening during stapedectomy or stapedotomy surgery.
CLINICAL CAVEAT: In cases of meningitis and
transmission of infection via the cochlear aqueduct
to the cochlea, rapid post-inflammatory ossification
of the cochlea can occur. This complicates or sometimes eliminates the option of cochlear implantation
in post-meningitically deafened individuals. In the
early years of cochlear implantation in the United
States, the normal six-month hearing aid trial was
foregone in cases of sensorineural hearing loss after
meningitis, in order to achieve implantation prior
to this labyrinthitis ossificans setting in.
THE FACIAL RECESS AND SINUS TYMPANI
Two important aspects of the posterior wall of the mesotympanum (middle ear) are the facial recess (FR) and
the sinus tympani (ST). The boundaries of the FR, from
lateral to medial, are the chorda tympani nerve medial
to the tympanic membrane, and the pyramidal process/
vertical facial nerve. The boundaries of the ST, from lateral to medial, are the pyramidal process and the promontory. Superiorly and inferiorly are the ponticulus and
the U-shaped subiculum, which are two small bony
ridges. The ponticulus is a horizontal “bridge” that runs
from the posterior border of the sinus tympani to the
posterior oval window. The subiculum is a thickened
piece of bone that runs from the posterior part of the
sinus tympani, overlying it and getting attached to the
border of the RWN. Sometimes this is described as a
“horse collar” that thickens at the posterior border of
the round window. The trough of the subiculum is posterior to the floor of the RWN. The ST can extend vertically, longer than expected.19 Examination of the sinus
tympani has been greatly enhanced with the development of otoendoscopes20 (Figure 6–41).
CLINICAL CAVEAT: In cholesteatoma surgery, the
ST and FR can be sites of hidden disease. Opening
the FR is accomplished either by drilling between
the CT and the FN or by taking down the posterior
external auditory canal and therefore exposing the
FR. This does not open the ST, however. The otologic surgeon must be careful to examine the ST,
either directly or with endoscopes, as even with a
canal-wall-down technique there can be keratin hidden away in it.
Temporal Bone Histology and Radiology Atlas110
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MID-MODIOLAR SECTION OF COCHLEA
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Temporal Bone Histology and Radiology Atlas112
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This mid-modiolar section of the human cochlea demonstrates the full 2¾ turns of the cochlea. The central
modiolus contains the ganglion cells of the cochlear
nerve. Osseous spiral laminae emerge from the modiolus to secure the basilar membrane medially. Laterally, the spiral ligament and stria vascularis are the
insertion points of the basilar membrane. Reissner’s
membrane separates the scala media which contains
endolymph from the scala vestibuli which, along with
the scala tympani, contains perilymph. Note the dense
otic capsule bone surrounding the cochlea.
The proximity of the cochlea to the cochleariform
(“spoon shaped”) process which guides the tensor
tympani tendon to the neck of the malleus is seen here.
Similarly seen is the relationship between the anterior
stapedovestibular joint—the annulus of the stapes
footplate—and the saccular membrane and macule as
well as the cochlea. Not seen in this particular section
is the fissula ante fenestram, an outpouching of connective tissue in continuity with the perilymph in the
vestibule just anterior to the anterior stapedovestibular
joint. That is the primary site of predilection for the development of otospongiosis.
21
SCALA MEDIA
The scala media of the cochlea is bounded by the basilar membrane inferiorly, separating it from scala tympani, and Reissner’s membrane superiorly, separating
it from scala vestibuli. The scala media contains endolymph and is the home of the organ of Corti, the sense
organ of the cochlea. Chapter 7 explains the microanatomy of the cochlea in detail. At this point, however,
the student should be able to recognize the following
structures. The tectorial membrane, which in life sits
on the cilia of the hair cells in the organ of Corti has in
this postmortem slide been pulled off so that it is only
attached medially at the inner sulcus. The inner sulcus
and outer sulcus, the spiral ligament, and the stria vascularis are identified. There is one row of inner (type 1)
hair cells and there are three rows of outer (type 2) hair
cells, with the Tunnel of Corti in between. The supporting cells are identified in Chapter 7. Rosenthal’s canal
transmits the nerve fibers from the organ of Corti to
the cochlear ganglion in the modiolus.
CLINICAL CAVEAT: Otosclerosis is symptomatic
in only 10% of cases. This is because otospongiotic
and otosclerotic changes involving only the fissula
ante fenestram or fossula post fenestram do not cause
hearing impairment. Only as the focus extends to
involve the stapedovestibular joint at the footplate
will the conductive hearing loss develop.
6. Horizontal Temporal Bone Sections with Corresponding Computed Tomography Images 113
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COCHLEAR ANATOMY
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ACKNOWLEDGMENTS
The authors wish to acknowledge Dr. Michael Paparella and Dr. Sebahattin Cureoglu for several of the histologic section pictures, and Dr. Ayala Rosenbaum for
several of the CT images.
REFERENCES
1. Hilding DA. Petrous apex and subarcuate fossa matura-
tion. Laryngoscope Oct. 1987;92;10:1129–1134.
2. Bluestone CD, Klein JO. Complications and sequelae: In-
tracranial. In: Otitis Media in Infants and Children, 4th ed.
Hamilton: BC Decker Inc.; 2007:436.
3. Samii M, Gerganov V. Microsurgical anatomy of the cer-
ebellopontine angle by the retrosigmoid approach. In:
Surgery of Cerebellopontine Lesions.Berlin: Springer Verlag;
2013:38.
4. Gradinego G. Sulla leptomeningite circoscitta e sulla
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Torino, 1904;10:59.
5. Huizing EH, De Grote JAM. Densitometry of the co-
chlear capsule and correlation between bone density loss
and bone conduction hearing loss in otosclerosis. Acta
Oto-Laryngologica April 1987;103(5–6):464–8.
6. House WF, Belal A Jr. Translabyrinthine surgery: anat-
omy and pathology. Am J Otol
7. Falcioni M, Fois P, Taibah A, Sanna M. Facial nerve func-
tion after vestibular schwannoma surgery. J Neurosurg,
Oct 2011;115;4:820–826, published online June 17, 2011;
DOI: 10.3171/2011.5.JNS101597.
8. Roosli C, Linthicum, Jr. FH, Cureoglu S, Merchant SN.
What is the site of origin of cochleovestibular schwannomas? Audiology & Neurotology. 2012;17(2):121–125.
9. Backous DD, Minor LB, Aboujaoude ES, Nager GT. Rela-
tionship of the utriculus and sacculus to the stapes foot-
. Apr 1980;1(4):189–198.
plate: anatomic implications for sound- and/or pressureinduced otolith activation. Ann Otol Rhinol Laryngol.
Jun;108(6):548–553.
10. Weissman JL, Hirsch BE. Beyond the promontory: the
multifocal origin of glomus tympanicum tumors. AJNR
Am J Neuroradiol. 1998 Jan;19(1):119–122.
11. Mullins WM, Gross CW, Moore JM. Long-term follow-
up of tympanic neurectomy for sialorrhea. Laryngoscope.
1979 Aug;89(8):1219–1223.
12. Pyykko I, Zou J, Zhang Y, Zhang W, Feng H, Kinnunen P.
Nanoparticle based inner ear therapy. World J Otorhino-
laryngol 2013;3(4):114–133.
13. Goycoolea MV, Lundman L. Round window membrane.
Structure function and permeability: a review. Microsc
Res Tech. 1997 Feb 1;36(3):201–211.
14. Chandrasekhar SS, Rubinstein RY, et al: Dexamethasone
pharmacokinetics in the inner ear. Otolaryngol Head Neck
Surg 2000 Apr; 122:521–528.
15. Watanabe H, Kysar JW, Lalwani AK. Microanatomic
analysis of the round window membrane by white light
interferometry and microcomputed tomography for mechanical amplification. Otol Neurotol 2014;35:672–678.
16. Vijayasekaran S, Halsted MJ, Boston M, et al. When is the
vestibular aqueduct enlarged? a statistical analysis of the
normative distribution of vestibular aqueduct size. AJNR
June 2007;28:1133–1138.
17. Bhimani S, Virapongse C, Sarwar M. High-resolution
computed tomographic appearance of the normal cochlear aqueduct. AJNR 1984;5:715–720.
18. Bhatt S, Halpin C, Hsu W, et al. Hearing loss and pneumococcal meningitis: an animal model. Laryngoscope. 1991
Dec;101(12 Pt 1):1285–1292.
19. Cheita AC, Maru N, Mogoanta CA, Ionita E. The recesses of the retro-tympanum. Rom J Morphol Embryol.
2010;51(1):61–68.
20. Marchioni D, Molteni G, Presutti L. Endoscopic anatomy
of the middle ear. Indian Journal of Otolaryngology and
Head & Neck Surgery. 2011;63(2):101–113.
21. Bretlau P. Relation of the otosclerotic focus to the fissula
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1999
CHAPTER 7
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The Cochlea, Vestibule,
and Central Connections
Hosakere K. Chandrasekhar
Three basic components comprise the sensory endorgan in the cochlea and the vestibule. They are: (1) sensory cells; (2) supporting cells; and (3) gelatinous matrices. The cochlear sensory endorgan is termed the
organ of Corti and that of the vestibular system is called
the crista in the semicircular canals and the macula in
the utricle and saccule.
ORGAN OF CORTI
This is the cochlear excitatory structure present within
the cochlear duct, which is the scala media of the cochlea. The principal cytologic structures include the
sensory cells known as hair cells and supporting cells
which are named the pillar cells, Deiter’s cells, Hen sen’s cells, and the inner and outer sulcus cells. The gelatinous matrix that canopies over these cells is called
the tectorial membrane (Figure 7–1).
There are approximately 12,500 outer and 3500 in ner hair cells. The outer (type 2) hair cells have an elongated cylindrical shape and are supported by Deiter’s
cells. The inner (type 1) hair cells are pear-shaped and
cells similar to Deiter’s cells support the inner hair cells
along the medial wall of the tunnel of Corti. (See Fig ure 2–9.) Hair cell apices are held by the reticular membrane. Each hair cell carries 50 to 150 stereocilia which
stand perpendicular to the tectorial membrane and
pi vot around their bases. The subcellular bodies of the
hair cells include a large nucleus, mitochondria, and
Golgi bodies. In each bundle of stereocilia there is one
stiff cilium called the kinocilium. The kinocilium is
at one edge of the hair cell; the stereocilia closest to it
are the longest ones, with their lengths becoming progressively smaller away from the kinocilium. The kinocilium is non-motile, while the stereocilia are motile, and it is fixed to the basal body on the tectorial
membrane.
Deiter’s cells have large cell bodies resting on the
basilar membrane. These cells exert a steadying influence on the hair cells and are presumed to secrete the
gelatinous matrix which is called the tectorial membrane. The tectorial membrane extends from the limbus over the organ of Corti. It wafts in the endolymph
with sound wave movement of the basilar membrane
and that excites the hairs of the hair cells in generating
the neural impulses translating that mechanical and
fluid energy into electrical energy ready to be transmitted along the cochlear nerve.
THE CRISTA AND THE MACULA
The three bony semicircular canal ampullae accommodate the membranous ampullae. Within the membranous ampulla a crest-like septum called the crista crosses
the base of the ampulla. The crista is made up of sensory
epithelium distributed on a mound of fibrous tissue,
blood vessels, and nerve fibers. A gelatinous cupula cov ers the mound and extends to the opposing wall of the
ampulla (Figure 7–2).
Ampullary hair cells are both types 1 and 2. Type 1
hair cells are found on the apex of the mound and type 2
hair cells are located on the slopes. The crista and cupula lie perpendicular to the plane of each semicircular
canal.
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