Skull Base Surgery of the Posterior Fossa

41

with an Adson Cerebellar Retractor to expose the
calvarium. The craniotomy opening is made in
the squamous portion of the temporal bone, mea-
suring approximately 5 × 5 cm and located
approximately two thirds anterior and one third
posterior to the external auditory canal (EAC) or
centered at the root of the zygoma. Anterior and
inferior placement of the craniotomy is critical to
ensure adequate exposure, particularly when
operating on the left ear. The bone flap is based at
the root of the zygoma as close to the floor of the
middle fossa as possible and can be fashioned
with a high-speed drill using a footplate attach-
ment to protect the underlying dura. The dura is
initially exposed in two corners of the bone flap
diagonal to one another, which allows separation
of the dura from the flap and introduction of the
footplate drill. Care must be taken when creating
the bone flap to avoid lacerating the dura, and the
extradural position of the footplate should be
confirmed periodically while drilling. It is some-
times necessary to remove additional bone along

the middle fossa floor with a cutting burr or ron-

geur once the craniotomy window is removed.

An alternative technique is to outline the entire

craniotomy flap with a high-speed drill using

standard cutting followed by diamond burrs. The

bone flap is set aside for replacement later.

The dura is elevated from the floor of the mid-

dle fossa with a suction irrigator and a blunt dural

elevator, with the initial landmark being the mid-

dle meningeal artery. This marks the anterior

extent of the dissection. If venous bleeding is

encountered in the area, it can be controlled with

either a slurry of powdered absorbable gelatin

sponge (Gelfoam) and thrombin or absorbable

knitted fabric (Surgicel). Dissection of the dura

proceeds in a posterior-to-anterior direction to

protect against injury to a potentially dehiscent

geniculate ganglion, which is seen in 5% of

cases. The petrous ridge is then identified poste-

riorly, and the superior petrosal sinus is elevated

from its groove at the time the true ridge is identi-

fied. The arcuate eminence and greater superfi-

cial petrosal nerve (GSPN) are identified, which

are the major landmarks in the intratemporal por-

tion of the dissection.

Once the dura is elevated, the Layla retractor

is placed over the medial ridge of the superior

petrosal sinus and locked in place to support the

temporal lobe. An alternative is the House-Urban

retractor, however the Layla retractor has a lower

profile and dual retractor blades to support the

widely elevated temporal lobe (Fig. 3.2) [ 38 ].

The GSPN is located medial to the middle men-

ingeal artery (Fig. 3.3). A large diamond drill

with continuous suction irrigation is used to iden-

tify the superior semicircular canal. Once this is

skeletonized and followed anteriorly, the genicu-

late ganglion is identified. As described by

Garcia-Ibanez, the IAC is located at the bisection

of the angle formed by the GSPN and the supe-

rior semicircular canal [ 39 ]. Bone is removed at

the medial aspect of the petrous ridge at this

bisection, identifying the IAC. This is taken later-

ally in the same axis of the external auditory

canal, exposing the dura of the posterior fossa

widely (2 cm), and the porus acusticus is exposed

for 270° circumferentially. As the lateral IAC is

approached, the surgical field tightens with the

Fig. 3.1 A preauricular curvilinear incision is made that
extends into the temporal scalp. Extension of this incision
to the inferior border of the tragus allows exposure of the
floor of the middle fossa

3 Middle Fossa and Translabyrinthine Approaches