Skull Base Surgery of the Posterior Fossa

171

When preoperative hydrocephalus or signifi-
cant perilesional edema is evident preoperatively,
insertion of an external ventricular drain before
starting the procedure can be of clinical benefit to
avoid intraoperative intracranial hypertension
and postoperative acute deterioration. The drain
is inserted preoperatively and opened at high
pressure or kept closed until the bone is removed.
Once this is done, the drain is opened, and CSF is
drained to allow for cerebellar relaxation just
before dural opening. The drain can be kept in
place to prevent postoperative CSF leak for few
days, and then a weaning trial is attempted. If the
trial fails, then a shunt should be inserted.
Most of these surgical cases can be done
with dynamic brain retraction using the suction

instrument in the nondominant hand; however,

when a fixed brain retractor is used, care must

be taken not to apply too much retraction on the

cerebellum to prevent cranial nerve (especially

seventh and eighth nerve complex) traction

injury or petrosal vein tears. During cyst wall

dissection off of the cranial nerve, manipula-

tion of the seventh and eighth nerve complex

should be avoided to prevent postoperative

facial nerve weakness or hearing loss. On the

other hand, the trigeminal nerve is more resil-

ient to manipulation and can be maneuvered

with impunity.

Approaching the supratentorial portion of the

cyst from the posterior fossa can be challenging.

Care must be taken not to injure the trochlear

Fig. 12.3 (continued) Patient positioning (a, b) and
microscopic (c–h) and endoscopic (i, j) views of left ret-
rosigmoid transtentorial approach for resection of a left
CPA epidermoid cyst with supratentorial extension into
the left middle fossa. (a) The patient is positioned in a
right lateral position with slight operative table reflex to
help with decreasing the venous congestion and bleeding.
(b) The location of the surgical incision in relation to the
sigmoid and transverse sinus. Note the extension of the
incision toward the left temporal bone in cases were a
middle fossa window for the supratentorial portion is
required. (c) Microscopic view of the left seventh and
eighth cranial nerve complex entering the internal audi-
tory canal after freeing the complex from the epidermoid
cyst. (d) Microscopic view of the fifth cranial nerve
pushed toward the seventh and eighth cranial nerve com-

plex as well as preservation of the petrosal veins. (e)

Microscopic view of the tentorial surface, tentorial free

margin, and the fourth cranial nerve. (f) Microscopic view

of the opening of the tentorium toward the incisura with

direct visualization of the fourth cranial nerve. (g)

Microscopic view of the removal of the supratentorial part

of the epidermoid cyst with identification of the left poste-

rior cerebral artery. (h) Microscopic view of the fourth

cranial nerve, the interpeduncular cistern, and the third

cranial nerve after partial removal of the supratentorial

part of the epidermoid cyst. (i) Endoscopic view of the

supratentorial compartment demonstrating a residual epi-

dermoid cyst located between the third cranial nerve and

the mesiotemporal lobe. (j) Endoscopic view shows the

removal of the a small piece of epidermoid cyst from the

Meckel’s cave around the fifth cranial nerve

12 Epidermoid Cyst