Skull Base Surgery of the Posterior Fossa

58

the jugular bulb and expose the presigmoid dura
(Figs. 4.2 and 4.6). The mastoid cortex is removed
en bloc prior to starting the mastoidectomy and
saved along with the craniotomy flap for eventual
reconstruction. The otic capsule and fallopian
canal are left untouched in order to protect hear-
ing and facial nerve function, respectively
(Fig. 4.2, inset; Fig. 4.6b).
Dura opening proceeds by creating a linear
incision along the floor of the middle cranial
fossa and extending the opening back toward the
tentorium, carefully preserving underlying
venous anatomy (Fig. 4.3). Another dural open-
ing is made in the presigmoid dura and expanded
toward the tentorium; this step often results in
sectioning of the endolymphatic sac. Once the
tentorium is exposed from above and below, the
superior petrosal sinus is controlled with coagu-
lation, and the tentorium is incised with careful
attention not to compromise any temporal lobe
veins (Fig. 4.3, inset). Attention is given to the
trochlear nerve at the medial tentorial edge,
which often lies just above the level of the tento-
rium. In cases of tentorial meningiomas, the ten-
torium is excised instead of cut. Once the cut

reaches the incisura, the sigmoid sinus is liber-

ated and may be retro-displaced which signifi-

cantly increases the presigmoid working room

afforded by the exposure (Figs. 4.4 and 4.6c)

Microsurgical tumor resection may now proceed

(Fig. 4.6d).

Combined Petrosal Approach

Patient Positioning

The patient is positioned in the same way as

described for the posterior petrosal approach.

Skin Incision and Craniotomy

The skin incision is similar to that described for

the posterior petrosal with slightly more anterior

bias of the anterior-most limb to allow additional

exposure of the middle fossa (Fig. 4.1).

A pedicled flap is elevated as described for

the petrosal approach consisting of the tempo-

ralis fascia along with the attachment to the

Fig. 4.2 Burr hole
placement and
craniotomy cuts shown
in the main figure. The
cuts overlying dura are
made with a craniotome
attachment, while those
overlying the sinus are
made with a drilling burr
( 2 ). Inset shows the
mastoidectomy which is
performed subsequent to
the craniotomy. The
facial nerve (FC) and the
semicircular canals (SC)
are shown here for
reference but are not
exposed during the
surgical approach in
order to protect them.
TM temporalis muscle,
SM sternocleidomastoid
muscle (Reproduced
with permission from
Al-Mefty [ 18 ])

D. Aum et al.