Skull Base Surgery of the Posterior Fossa

42

labyrinthine portion of the facial nerve lying
immediately posterior to the basal turn of the
cochlea. The dissection must consequently narrow

to approximately 90° to avoid the cochlea and

superior semicircular canal. The posterior fossa

dura is opened with a microblade (No. 59; Beaver

Company), and the CSF is released, resulting in

temporal lobe relaxation. At the fundus of the

IAC, the vertical crest (Bill’s bar) and the laby-

rinthine facial nerve are exposed.

The dura of the IAC is incised along the poste-

rior aspect, and the facial nerve is identified in the

anterior portion of the IAC (Fig. 3.4). The supe-

rior vestibular nerve is divided at its lateral end.

The tumor is separated from the facial nerve

under high magnification, beginning at Bill’s bar

and dissecting from medial to lateral (Fig. 3.5).

The arachnoid is divided, the edge of the facial

nerve identified, and the facial-vestibular anasto-

mosis is sharply cut. This prevents excess trac-

tion on the facial nerve that can lead to

neuropraxia. Intracapsular debulking can be per-

formed, if needed, with microscissors and cup

forceps. Again, tumor removal proceeds in the

medial to lateral direction, here to prevent trac-

tion on the cochlear nerve and its blood supply as

it enters the modiolus. The inferior vestibular

nerve can be left in place if uninvolved in an

Fig. 3.2 The craniotomy window is placed two thirds
anterior to the external auditory canal. A variety of retrac-
tors can be used to support the temporal lobe

Fig. 3.3 The greater
superficial petrosal
nerve is visible on the
floor the middle fossa. It
is immediately medial to
the middle meningeal
artery. The superior
semicircular canal is
medial to the arcuate
eminence. The internal
auditory canal can be
located by bisecting the
angle formed by the
greater superficial
petrosal nerve and the
superior semicircular
canal

J.C. Sowder et al.