Skull Base Surgery of the Posterior Fossa

156

the area of the porus acusticus and the CSF is
allowed to egress, more brain relaxation and bet-
ter middle fossa retraction can be accomplished.
This will allow for better surgical trajectory to the
lateral aspect of the IAC and cochlear nerve.
The facial nerve is identified first in the
medial portion of the IAC proximal to the tumor
using the facial nerve stimulator, and then the
proximal vestibular nerve is divided sharply. The
tumor is now elevated slowly and gently from
the facial nerve and the cochlear nerve in a
medial-to- lateral direction to minimize the risk
of tearing the cochlear nerve fibers entering the
lamina cribrosa from the hair cell. In some cases,
tumor debulking is completed using a microscis-
sor or ultrasonic aspirator to facilitate tumor
manipulation and dissection from the facial and
cochlear nerve. A sharp hook is used to create
the plan between the tumor and the facial and
cochlear nerves and to divide the facial-vestibu-
lar communication fibers. Bipolar cautery is
avoided during this surgery to prevent thermal
injury to the delicate facial and cochlear nerve.
Bleeding in these small tumors in the IAC is
minimal and usually controlled easily with
hemostatic agents and continuous irrigation;
however, when bleeding obscures the dissection
plan and the surgical cavity, the operative table

can be placed in reverse Trendelenburg position

to decrease the venous congestion and allow the

blood and the irrigation to egress out of the sur-

gical field until the tumor is completely removed.

Care must be taken not to injure the labyrinthine

artery or its branches during tumor dissection.

Any exposed air cells are sealed off using bone

wax. After hemostasis is achieved, a small piece

of fat is harvested from the abdomen or thigh

and placed over the IAC. The lower margin of

the craniotomy is inspected for any open air

cells, and bone wax is used to seal them. The

bone flap is placed back, and the lower end of the

drilled bone is covered using a small piece of

MEDPOR cranioplasty (Fig. 11.5). Temporalis

muscle is closed as a separate layer followed by

closure of the fascia, galea, and skin. A routine

postoperative CT scan of the brain is obtained

showing the surgical corridor and the amount of

bony drilling (Fig. 11.6).

Limitations of the MFA

Although it offers a short operative time and easy

approach with minimal morbidity and mortality

for carefully selected patients with VSs, there are

several limitations to the MFA. The surgical cor-

Fig. 11.6 Axial (a) and coronal (b) CT scan brain bone window demonstrating the extent of the bone removed during
middle fossa approach to reach the right IAC postoperatively

G. Alzhrani et al.