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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_4399_Библиотеки_им_академика_М_И_Перельмана
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Temporal Bone Histology and Radiology Atlas96
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HORIZONTAL SECTION 9
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Temporal Bone Histology and Radiology Atlas100
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HORIZONTAL SECTION 10
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Temporal Bone Histology and Radiology Atlas104
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CLINICAL CAVEAT: Note the intimate relationship between the lateral wall of the carotid artery
to the medial wall of the osseous ET, as seen in
Horizontal Section 8 and 10 Radiograph. Attempted
dilatation of the bony ET could result in carotid artery injury and secondary sequelae. Currently, surgery for ET dilatory dysfunction is performed in the
cartilaginous ET and minimizes the risk of carotid
artery wall fracture/clot/embolus.
HORIZONTAL SECTION 11
Horizontal Section 11 is an inferior horizontal histologic section demonstrating the relationship between
the round window membrane and scala tympani of
the basal turn of the cochlea (containing perilymph)
with the cochlear aqueduct leading to the subarachnoid space. Also seen here are the chorda tympani
nerve in iter chordae posterior, just medial to the membranous annulus of the tympanic membrane; the facial
recess—bounded laterally by the chorda and medially
by the facial nerve; the facial nerve; the stapedius muscle which lies immediately anterior to the vertical lie of
the facial nerve; the sinus tympani—bounded laterally
by the facial nerve and medially by the inner ear; the
posterior semicircular canal (PSCC); the singular nerve
which supplies the crista of the PSCC and fuses with
the inferior vestibular nerve in the internal auditory
canal (IAC)—not shown here; and Jacobson’s nerve on
the promontory.
Jacobson’s nerve is the tympanic branch of the
ninth cranial nerve—the glossopharyngeal nerve, arising from its inferior ganglion. It also carries pregangli-
onic parasympathetic fibers from the inferior salivary
nucleus, which eventually enter the otic ganglion. Jacobson’s nerve enters the middle ear cavity via the inferior tympanic canaliculus and contributes to the tympanic plexus located on the cochlear promontory. The
parasympathetic fibers leave the plexus as the lesser petrosal nerve.
CLINICAL CAVEAT: Jacobson’s nerve has two
important roles in otolaryngologic pathology. The
neuroendocrine cells of this nerve give rise to glomus tympanicum tumors, which are often identified early as small vascular spheres on the promontory. It has been shown, however, that glomus
tympanicum tumors may arise from multiple sites
on the medial wall of the middle ear.10 In cases of
severe hypersalivation and drooling, sectioning of
bilateral Jacobson’s nerves (severing all branches
of the tympanic plexus) and bilateral chorda tympani nerves can be effective in ¾ of patients.
11
THE ROUND WINDOW MEMBRANE
The round window membrane (RWM), also known as
the “secondary tympanic membrane,” marks the termination of the cochlear duct at the basilar turn. It lies
within the round window niche (RWN) and is perpendicular to the lie of the oval window (OW). The opening of the RWN, however, is often in a similar plane to
the oval OW, and can be obscured by a thin adhesion.
6. Horizontal Temporal Bone Sections with Corresponding Computed Tomography Images 105
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CLINICAL CAVEAT: The novice otologic surgeon
may mistake an adhesion across the RWN as the actual RWM. It is important to keep in mind that, similar to other right angle relationships in the ear, the
OW and the RWM are at approximately 90 degrees
to each other. Proper exposure of the actual RWM is
often accomplished by at least removal of that adhesion, if not removal of a portion of the bone of the
RWN. This becomes important for any procedure
needing access to the RWM, including cochlear or
active middle ear device implantation, fistula repair, and application of intratympanic medications
to the cochlea.
The RWM is a semipermeable membrane made
up of an outer epithelium, an inner core of connective
tissue, and an inner epithelium.12 The RWM is thickest in humans, at 70 µm. Permeability factors include
size, concentration, liposolubility, and electrical charge
of the substrate, as well as thickness of the membrane.
Passage of substances through the RWM is by different
pathways, decided at the outer epithelium.13
The shape of the RWM is also of importance. It has
a large area of flat surface along with a concave and
convex structure with a saddle point at which negative and positive curvatures manifest themselves in
different directions. This is shown by micro-computed
tomography, white laser interferometry, and stitching
together of the data sets acquired by those means sepa-
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rately,
and is important in the development of active
middle-ear hearing transducers placed at the RWM.
CLINICAL CAVEAT: Semi-permeability of the RWM
is important in protection of the inner from middle
ear pathogens, such as those causing otitis media.
The permeability of the RWM to certain agents
such as aminoglycoside antibiotics and steroids has
enabled the growth of interest in, and application
of, intratympanic injections for various inner ear
diseases including Meniere’s disease and sudden
sensorineural hearing loss. There are agents that,
when applied topically, increase permeability of the
RWM and can therefore be used as facilitators of
transport across the RWM. These include histamine
and hyaluronic acid.
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THE COCHLEAR AND
VESTIBULAR AQUEDUCTS
The vestibular aqueduct (VA) lies in a plane perpendicular to the IAC and transmits the endolymphatic duct
and sac. Lateral to the sac, the opening to the posterior
fossa is covered by the operculum, a shelf of bone on
the posterior surface of the temporal bone that protects the endolymphatic sac from the pulsations of the
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