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TitleAnatomy of the Temporal Bone with Surgical Implications 3rd ed. - A. Gulya (Informa, 2007) WW
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Page 189


A common anatomic variant is a localized area of widening (cupping)
in the anterior wall of the canal (Figs. 44 and 45).

The exposure of the internal auditory canal and its contents by way of a
middle cranial fossa approach, popularized by House (182), has been success-
fully used for removal of small vestibular schwannomata, for vestibular
and/or cochlear nerve section, and for facial nerve decompression. This
approach to the internal auditory canal demands a thorough knowledge of the
normal anatomy as well as of the typical variations one may encounter. In the
House (182) approach, once the squamosal craniotomy has been performed,
the middle meningeal artery entering the cranium via the foramen spinosum
is the first intracranial landmark to be identified; it forms the anterior limit of
dissection. Further dural elevation is carried out to expose the arcuate emi-
nence posteriorly and the superior petrosal sinus medially. The greater super-
ficial petrosal nerve, a crucial landmark in the localization of the internal audi-
tory canal, is next identified and dural elevation proceeds posteriorly, parallel
to its course. The geniculate ganglion serves as a reference point for further
dissection. The facial nerve is medial to the geniculate ganglion, while the
superior canal is posteromedial to it. The exposure of the internal auditory
canal is achieved by drilling in the area between the superior canal and the
basal turn of the cochlea just medial to the geniculate ganglion. Medial dissec-
tion follows the facial nerve up to the ridge of the superior petrosal sinus
corresponding to the superior lip of the porus acousticus. This dissection is
facilitated by the anteromedial divergence of the internal auditory canal from
the superior canal, which widens the surgical field.

Suggestions have appeared in the literature that a narrow internal
auditory canal may cause sensorineural hearing loss and vertigo, and that
surgical decompression of the canal is an appropriate therapy (183). Pérez
Olivares and Schuknecht (181) studied 144 temporal bone specimens from
subjects with a history of slowly progressive sensorineural hearing loss and
found a distribution of canal dimensions similar to that of normals; they also

Figure 43
The internal auditory canal in this ear
measures 12 mm in length (normal:
8 mm), which is considered to be a
normal anatomic variant (female, age
90 yr).

Page 190


reported the absence of any soft tissue lesions which could have caused a
canal narrowing. Hence, they believe that radiologic documentation of a
small internal auditory canal is merely coincidental to, and not causative of,
cochlear and/or vestibular peripheral symptomatology.

Parisier (184) conducted a temporal bone study, utilizing both dis-
sected and serially sectioned specimens, to examine the variations in
anatomic landmarks used in the middle cranial fossa approach. He found
that those structures which were of otic placode derivation and encased in

Figure 44
The internal auditory canal measures
7.5 mm in length, which is considered
to be normal. The cupping at its ante-
rior aspect is an occasional occurrence
that may create a diagnostic dilemma
on imaging studies. The pathologically
thin replacement membrane is the
result of a healed perforation. As a
result, the manubrium is medially dis-
placed because of lessened opposition
to the traction of the tensor tympani
muscle (male, age 46 yr).

Figure 45
The temporal bone of a 66-yr-old man
shows anterior cupping of the middle
portion of the internal auditory canal
(IAC) occurring as an anatomic variant.

Page 377

356 � INDEX

Vascular supply, of auricle (pinna) (cont.)
of inner ear, 216–218, 217, 220
of middle ear, 210–215, 211
of facial nerve, 189, 189

Vein(s), cardinal. See Embryology, of veins, cardinal
cochlear, inferior, 164–165, 220, 220
in fallopian canal, 60, 189, 189, 206, 207
jugular, internal, 4, 20, 206, 236s

superior location of bulb, 206–208, 207, 210
mastoid emissary, 205
of cochlea, 219, 220, 220
spiral, anterior and posterior, 217, 218, 219, 220, 220

Venous plexus, pericarotid, 10
Venous sinus, lateral, 202–203, 204–206, 226s, 228s,

242s, 249s
Venous supply, of endolymphatic sac, 161, 161

of membranous labyrinth, 220
Vertical crest, fundus of internal auditory

canal, 24s, 166, 167
Vertical sections of temporal bone, 14, 14–22

Vesiculations of semicircular duct(s), 145
Vestibular aqueduct, 155–156, 161

radiologic studies of, 156
Vestibular cecum of cochlear duct, 26s, 137
Vestibular crest, vestibule, 137
Vestibular nerve. See Nerve(s), vestibular
Vestibule, 137–138

measurements of, 90
perilymphatic cistern of, 10, 18

Vestibulocochlear (Oort’s) anastomosis, 193
Vestibulofacial anastomosis, 193, 194
Voit’s anastomosis, 193

Wax, ear (cerumen), 37

Zona(e) arcuata and pectinata, 146, 148
Zygomatic area and cells, Pneumatization of,

123, 129
Zygomatic process, 1

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