Skull Base Surgery of the Posterior Fossa

152

acusticus in a lateral-to-medial direction [ 12 ]. The

Fisch technique exposes the blue line of the SSC,

and the IAC plane is approximated by drawing an

imaginary line angled 60° to the SSC plane directed

toward the posterior fossa dura [ 9 ]. Both techniques

expose the IAC in a lateral-to-medial direction

where the facial nerve is most superficial in the

petrous bone, increasing the risk for facial nerve,

SSC, and cochlear injury. The Garcia-Ibanez tech-

nique uses the GSPN and AE to locate the IAC [ 10 ].

The IAC is localized using a line bisecting the angle

between GSPN and AE, and then the drilling is

directed toward the porus acusticus to expose the

IAC in a medial-to-lateral direction, decreasing the

risk for facial nerve injury; this technique does not

require exposure of the SSC. Another less popular

technique involves drilling a point away from the tip

of the GG about 9.9 mm on a line angled with the

GSPN about 96° [ 17 ].

Given the variation in the middle fossa anat-

omy, there is no one technique fit for all patients.

We generally prefer the Garcia-Ibanez technique

(Fig. 11.4) because of the lower risk for injuring

the facial nerve and inner ear structures.

Surgical Technique

Bony Exposure

After general anesthesia and intubation, the

patient is positioned in either a completely lateral

position with the side of the surgery up and the

head fixed in a Mayfield head clamp or a supine

position with small shoulder post under the ipsi-

lateral side with head turned 60° to the contralat-

eral side (Fig. 11.5). We tilt the head toward the

contralateral shoulder until the ipsilateral sig-

moid sinus becomes parallel to the floor. Facial

nerve monitoring and auditory BAER are used

routinely for all VS cases. A lazy “S” skin inci-

sion is marked starting at the zygomatic root just

anterior to the tragus and then extending superi-

orly, curving posteriorly and then anteriorly just

above the superior temporal line and behind the

coronal suture. Preoperative antibiotics, dexa-

methasone, and mannitol are administered. The

incision line is injected with local anesthetic and

a vasoconstrictor, after which the skin incision is

Fig. 11.4 (a) Cadaveric dissection (right-sided approach)
photograph demonstrating the anatomy of the middle
fossa. The temporal lobe is elevated extradurally to expose
the floor of the middle fossa. This is performed in a poste-
rior-to-anterior direction to avoid traction injury to the
facial nerve by putting stretch on the greater superficial
petrosal nerve (GSPN). The horizontal segment of the
petrous internal carotid artery (ICA) is visible through a
bony dehiscence. The arcuate eminence (AE) initially is
identified along the petrous ridge. Extradural elevation
then is continued anteromedially to expose the geniculate
ganglion (GG) and the GSPN. The middle meningeal
artery at the foramen spinosum (FS) is divided to allow
further release of the temporal dura from the middle fossa
cranial base to expose the posterior cavernous sinus and
the V2 and V3 branches of the trigeminal nerve. (b)
Cadaveric dissection photograph showing the middle
fossa rhomboid (red) is bordered by the V3 anteriorly, the
GSPN laterally, the AE posteriorly, and the petrous edge
medially. The horizontal segment of the petrous ICA
courses parallel to and beneath the GSPN. The internal
auditory canal (IAC, blue dotted line) lies approximately
in the plane that bisects the angle between the GSPN and
AE. The cochlea (C) is situated anteromedial and inferior
to the geniculate ganglion. Glasscock’s triangle (blue) is
bordered by the posterior rim of the foramen ovale, the
foramen spinosum, the posterior border of V3, and the
cochlear apex. (Liu et al. [ 18 ], by permission of Congress
of Neurological Surgeons [ 18 ])

G. Alzhrani et al.