60
SCM and retracted. The zygomatic arch is
exposed, and osteotomies are made along the
root of the zygoma and as anterior as possible
just behind the maxillary eminence. The
zygoma is left in situ to preserve the attach-
ments of the masseter muscles, but reflected
inferiorly along with the temporalis muscle;
this additional maneuver allows retraction of
the temporalis muscle caudally into the infra-
temporal fossa, thus providing unhindered
access to the middle cranial fossa floor.
Burr holes flanking the transverse sinus are
placed similar to the petrosal approach, with an
additional burr hole added anteriorly along the
floor of the middle fossa near the temporal root of
the zygoma. Burr holes are connected as previ-
ously described, and a bone flap is created that
encompasses a larger component of the temporal
squamosa. A mastoidectomy is performed as
described in the previous section, skeletonizing
the sigmoid sinus to the level of the jugular bulb
and exposing the presigmoid dura.
Prior to elevating the temporal dura off the
middle cranial fossa floor, a small dural opening
is made in the presigmoid area and cerebrospinal
fluid is released. The temporal lobe is elevated
from the middle cranial fossa floor, proceeding
in a posterior-to-anterior direction in order to
more readily identify the greater superficial
petrosal nerve (GSPN). During the dissection
attention should be given to the presence of bony
dehiscences; various structures including the
geniculate ganglion of the facial nerve and the
carotid artery may lack a roof and thus be at risk
of iatrogenic injury. There is also frequently sig-
nificant thinning or frank dehiscence in the teg-
men tympani. The middle meningeal artery is
identified at the foramen spinosum, cauterized
and cut. The foramen spinosum is packed with
bone wax. The extent of extradural dissection of
the lateral wall of the cavernous sinus is tailored
to the extent of sinus involvement with tumor.
The inferior aspect of the third division of the
trigeminal nerve is dissected and elevated, which
aids in the subsequent mobilization of the tri-
geminal nerve and the Gasserian ganglion dur-
ing the anterior petrosectomy.
The anatomical landmarks along the middle
cranial fossa floor are identified including the
arcuate eminence, trigeminal depression and tri-
geminal prominence, the second and third tri-
geminal divisions, and their respective foramina.
The petrous carotid canal is unroofed in order to
definitively locate the horizontal segment of the
petrous carotid artery. A Fogarty balloon may be
placed along the carotid artery within the canal,
which can be inflated in the event of vascular
injury in order to obtain proximal control [ 14 ]. At
this point, anterior petrosectomy can proceed by
drilling the bone of the petrous apex within
Kawase’s triangle from the internal auditory
canal to the petroclival junction, taking care to
avoid the cochlea which is located at the postero-
lateral aspect of the exposure.
Dural opening is similar to that described for
the posterior petrosal approach except that the
temporal dura opening can extend more anteri-
orly to take advantage of the additional space cre-
ated by the anterior petrosectomy.Tumor Resection
The main determinates of the extent of resection
possible for lesions of the skull base include the
presence of an arachnoid dissection plane, the
consistency of the tumor, and the tumor’s level of
adherence to surrounding neurovascular struc-
tures; particularly fragile for this location are the
basilar artery perforators. For meningiomas, by
virtue of having performed a petrosectomy, the
blood supply would have already been inter-
rupted. Once reasonable devascularization is
achieved, the tumor is incised and the tumor deb-
ulked using suction or an ultrasonic aspirator;
significant debulking will allow dissection of the
development of the intra-arachnoidal plane for
dissection preserving neurovascular structures.
Involved bone, either grossly or radiographically,
should be removed using a high-speed drill.D. Aum et al.