96
tumors extending along lower third of the clivus
and contralaterally along the ventral brainstem to
optimize the surgical trajectory with limited
brainstem traction [ 1 , 3 , 4 , 11 ]. In addition,
suprameatal extension of the conventional retro-
sigmoid suboccipital approach enhances the sur-
gical access to Meckel’s cave, an area commonly
involved by these tumors (Fig. 7.1). The suboc-
cipital approaches are described in depth else-
where [ 1 , 3 , 4 , 11 ].
Transpetrosal Approaches
Anterior Transpetrosal (Kawase’s)
Approach
Indications and Limitations
Small- to moderate-sized PC tumors centered on
the petrous apex, which have a smaller supraten-
torial component and a larger infratentorial com-
ponent, are good candidates for the anterior
petrosal (Kawase) approach. It is an extremely
handy approach that can be utilized for a large
proportion of PC meningiomas. It has the advan-
tage of providing direct access along the long
axis of the tumor, offers the ability to devascu-
larize the tumor first by drilling the involved
bone extradurally and coagulating the dura mater
feeders to the tumor, and carries lower risk of
iatrogenic injury to vestibulocochlear apparatus
and facial nerve. However, tumors extending lat-
eral to internal acoustic canal (IAC) and inferior
to the lower third of the clivus are difficult to
access adequately using just this approach,
which often needs to be combined with a poste-
rior transpetrosal approach. There is also a risk
of venous embarrassment of the temporal-pari-
etal region with elevation of the middle fossa
dura during dissection.
Surgical Technique and Nuances
Use of an intraoperative lumbar drain may be
beneficial to prevent retraction injury to the tem-
poral lobe. The patient is positioned supine in a
comfortable beach chair position, with the head
turned to contralateral side with slight extension
so that the superior sagittal sinus is approxi-
mately parallel to the floor. This may be altered
if a frontotemporal craniotomy is used, where
the head is turned about 45° from midline. The
pressure points are padded to prevent pressure
sores and compression neuropathy. Intraoperative
electrophysiological monitoring is useful in rul-
ing out any positioning-related neurological def-
icits, which are reversible if identified early.
Once the patient is positioned, the incision is
marked in a small reverse question mark shape
(based on the anterior division of superficial
temporal artery and supratrochlear artery) or
with a quadrangular flap (based on the posterior
division of superficial temporal artery and poste-
rior auricular artery) along the temporal area.
The craniotomy is centered on the external audi-
tory meatus and the root of the zygoma, flush
with the skull base. Any opened air cells along
the root of the zygoma and mastoid region are
evaluated and filled with wax during bony expo-
sure. Via an extradural approach, the two layers
of the lateral cavernous sinus wall are separated
so that the gasserian ganglion and inferior aspect
of V3 are exposed adequately [ 20 ]. Next, the
middle meningeal artery is identified ~2 cm infe-
rior to the root of the zygoma, where it is coagu-
lated and divided where it enters the foramen
spinosum, just lateral and posterior to the fora-
men ovale. The greater superficial petrosal nerve
(GSPN) is identified running posterior to the
middle meningeal artery and is dissected free off
the dura from a posterior- to- anterior trajectory to
avoid traction and injury to the geniculate gan-
glion. The arcuate eminence is the next structure
to be identified; it represents the upward projec-
tion of the superior semicircular canal (SCC).
Once the boundaries of Kawase’s triangle are
identified—anteriorly the V3 nerve, laterally the
GSPN, posteriorly the IAC, and medially
Meckel’s cave—the drilling can be safely per-
formed to expose the posterior fossa dura mater.
Dura is opened parallel to the base of the tempo-
ral lobe, followed by ligation of the superior
petrosal sinus (SPS) proximal to the drainage of
vein of Labbé. The tentorium is incised posterior
to the entry of the trochlear nerve in its free mar-
gin to combine the supra- and infratentorial
access [ 20 ].A. Raheja and W.T. Couldwell