Skull Base Surgery of the Posterior Fossa

45

intersection with the superior canal (crus com-
mons) superiorly and its ampullated end anterior-
inferiorly, which marks the inferior border of the
IAC. Caution must be taken to prevent damage to
the mastoid segment of the facial nerve here.
Bony removal proceeds inferiorly until the jugu-
lar bulb is identified at the same level as the IAC.
The superior canal is opened along its entire path
toward its ampulla, taking care not to violate the
temporal lobe dura superiorly. The subarcuate
artery is often encountered in the center of the
arch of the superior canal, marking the superior
border of the IAC [ 16 ]. All of the remaining bone
between the vestibule and the jugular bulb is
removed (Fig. 3.9).
Prior to opening the IAC, which begins deep
to the vestibule and runs anteriorly away from the
surgeon, its dura must be exposed in 270°. The
cochlear aqueduct enters the posterior fossa in
between the IAC and the jugular bulb and marks
the inferior limit of bone removal. The bone is
removed anterior to the cochlear aqueduct

between the inferior IAC and jugular bulb to

facilitate exposure to the inferior aspect of the

tumor. Care is taken not to remove bone deep to

the cochlear aqueduct to prevent injury to con-

tents of the jugular foramen [ 42 ]. Bone superior

to the IAC is removed last due to its location near

the facial nerve in order to expose the superior

aspect of the tumor (Fig. 3.10).

Prior to opening the dura, we vigorously irri-

gate the cavity with bacitracin solution to remove

the bone dust. The posterior fossa dura is incised

sharply over the midportion of the IAC with a

microblade (No. 59; Beaver Company) and scis-

sors. This incision is extended along the IAC and

arches superiorly and inferiorly around the porus

acusticus in a Y shape. For large tumors, the inci-

sion may need to be extended toward the sig-

moid sinus [ 16 ]. Hemostasis is obtained with

bipolar electrocautery. The arachnoid is opened

with a sharp hook, allowing the egress of some

CSF. At this point, only fenestrated suction tips

should be used.

Fig. 3.8 The labyrinthectomy is carried out, the facial
nerve is skeletonized, and the bone is removed between
the jugular bulb and the internal auditory canal

Fig. 3.9 The posterior fossa and middle fossa dura are

exposed. Exposure of the middle fossa dura is important

to allow for extradural retraction of the cerebellum

3 Middle Fossa and Translabyrinthine Approaches