Skull Base Surgery of the Posterior Fossa

44

sulcus. The surgical site is prepped and draped in
similar manner as the middle fossa approach.
A hockey stick-shaped retroauricular skin inci-
sion that extends behind the mastoid tip is made
with a No. 15 blade down to the temporalis fascia,
hemostasis is obtained, and an anterior-based
skin flap is elevated. A standard anterior-based
periosteal flap is elevated with a Lempert eleva-
tor, and the mastoid cortex is exposed. Care must
be taken not to violate the EAC skin when elevat-
ing the flap to prevent postoperative CSF otor-
rhea. Adson Cerebellar Retractors are placed at
right angles to one another to retract the soft tis-
sues. Temporalis muscle can be harvested at this
time and placed on the back table to use for
eustachian tube packing, if planned. A cortical
mastoidectomy is performed with a high-speed
drill, large cutting burrs, and suction irrigation.
The dura should be exposed along the sigmoid
sinus and tegmen at the sinodural angle, which
is the deepest point of the dissection. The bone
is removed 2 cm posterior to the sigmoid sinus
to adequately expose the posterior fossa dura.
A thin shell of bone is left over the sigmoid sinus
(Bill’s island) to protect it from the shaft of
the burr during the labyrinthectomy (Fig. 3.7).
Some surgeons decompress the sigmoid sinus
completely to facilitate retraction to improve

exposure. The sinodural angle should be opened

as far posteriorly as possible to facilitate a tan-

gential view of the vestibule, which lies medial to

the facial nerve [ 40 ]. We routinely open the

facial recess, remove the incus, and pack the

eustachian tube to prevent a route of egress of

CSF. Alternatively, the facial recess bone and

incus can be left intact. After tumor dissection,

muscle can be packed around the incus in an

effort to seal off the middle ear from the temporal

bone defect and posterior fossa CSF flow [ 41 ].

The mastoid facial nerve is identified and fol-

lowed down to the stylomastoid foramen.

A labyrinthectomy is performed with small

(3–4 mm) cutting burrs (Fig. 3.8). The semicircu-

lar canals initially are skeletonized. The canals

are then serially fenestrated and opened com-

pletely on a broad front, beginning with the hori-

zontal semicircular canal. It is important to open

on a broad front to provide continuous land-

marks. The horizontal canal is opened down to its

intersection with the posterior canal. The poste-

rior canal is opened in a similar fashion up to its

Fig. 3.6 The tumor is completely removed and the ves-
tibular nerves are divided, to avoid a postoperative partial
vestibulopathy

Fig. 3.7 The mastoidectomy is carried out with exposure

of the sigmoid sinus, vertical facial nerve course, and

labyrinth

J.C. Sowder et al.