Skull Base Surgery of the Posterior Fossa

17

Fig. 1.8 Mastoidectomy. (a) Lateral view of the right
mastoid process. The mastoid part of the temporal bone is
posterior to the external auditory canal. The limits of the
mastoidectomy are the asterion, the suprameatal crest, and
the mastoid tip. (b) Mastoid air cells are drilled until the
antrum is encountered, leading to the middle ear elements
and the corticated labyrinthine structures. (c) The presig-
moid posterior fossa dura is outlined by Trautman’s tri-
angle roughly between the superior petrosal sinus, the
sigmoid sinus, and the jugular bulb. The posterior semicir-

cular canal faces the posterior fossa dura and the superior

semicircular canal faces the middle fossa dura. (d)

Enlarged view of the labyrinth through a mastoidectomy

exposure. The facial nerve bends inferiorly below the lat-

eral semicircular canal to begin its mastoid segment in the

anterior part of the mastoidectomy exposure. The short

process of the incus points to this portion of the facial

nerve. The chorda tympani courses further anterior than

the facial nerve, and the space between them (facial

recess) can be drilled to expose the tympanic cavity

Fig. 1.7 (continued) portion of Meckel’s cave. (c)
Extensive drilling of the suprameatal tubercle can be com-
bined with division of the tentorium and superior petrosal
sinus to increase exposure of Meckel’s cave. (d) Posterior
exposure of the internal auditory canal (IAC). The internal
auditory meatus is opened, and the nerve rootlets have
been identified. The anterior inferior cerebellar artery
(AICA) often loops near these nerves. The labyrinthine
artery also enters the IAC and its injury can lead to deaf-
ness. (e) Posterior view of the internal auditory canal and
its nerves. The facial nerve is anterior and superior, and
together with the superior vestibular nerve, is separated
from the cochlear and inferior vestibular nerve by the
transverse crest. The nervus intermedius carries sensory

and parasympathetic fibers of the facial nerve. A loop of

AICA often protrudes into the IAC and can cause genicu-

late neuralgia by impinging upon the nervus intermedius.

(f) Posterior view of the far-lateral exposure. The far-

lateral approach is an inferior continuation of the retrosig-

moid approach, adding additional exposure through the

foramen magnum, occipital condyle, and lamina of the

atlas. (g) Far-lateral/transcondylar approach. The verte-

bral artery has been mobilized from the C1 transverse

foramen, and the occipital and atlantal condyles have been

drilled to expose the hypoglossal canal and to increase

exposure of the lower clivus. An extradural PICA origin is

seen. The jugular tubercle can be drilled to increase

anterior exposure

1 Surgical Anatomy of the Posterior Fossa