155made down to the galea. This is followed by
opening the temporalis fascia and muscle using a
monopolar cautery down to the bone. The skin
incision is often extended inferiorly over the
zygomatic root to allow for a wider exposure
when the retractors are placed. Care must be
taken not to injure the frontal branch of the facial
nerve below the zygomatic arch. A periosteal
elevator is used to dissect the temporalis along
with the periosteum from the bone anteriorly and
posteriorly, making sure the root of the zygoma is
completely exposed and centered at the lower
margin of the bony exposure. A self-retaining
retractor is placed, and two bur holes are made.
One bur hole is placed just above the root of the
zygoma and the other one just above the squamo-
sal suture in the same plan. A craniotome is used
to make the bony cuts; and a bone flap (~5 ×
5 cm) is elevated while maintaining the integrity
of the dura, which is then tacked up to the edge of
the craniotomy superiorly. The lower edge of the
craniotomy is made flush with the middle fossa
floor using a cutting drill. Air cells of the tempo-
ral bone may be encountered in some cases and
must be closed using bone wax to prevent the risk
of CSF leak. Under microscopic visualization,
the dural elevation is commenced. A small suc-
tion and a dural dissector are used to elevate the
dural from the middle fossa floor. This process is
started by identifying the foramen spinosum and
the MMA in the middle fossa floor, which is con-
sidered a very important landmark. The foramen
spinosum is always located posterolateral to the
foramen ovale and V3, so injury of the GSPN at
this stage of the operation is unlikely. We then
identify the foramen ovale and the V3 anteriorly
and medially. The foramen spinosum and ovale
with the MMA and V3 mark the anterior limit of
the surgical exposure. The MMA is coagulated
and divided sharply, which will release the dural
tethering and ease the dural elevation to identify
the foramen ovale and V3. Bipolar cautery is
avoided in this area to prevent thermal injury to
the GSPN or GG. Bleeding from small emissary
veins from both foramina is not uncommon and
is easily controlled by using a hemostatic agent.
Once that is done, attention is turned toward the
petrous ridge posteriorly, where the dura is ele-
vated from lateral to medial along the ridge, iden-
tifying the tegmen, AE, meatal depression, and
trigeminal prominence. The trigeminal impres-
sion and petrous apex do not need to be exposed.
Dissection then is continued in a posterior-to-
anterior direction along the floor of the middle
fossa toward the foramen ovale to identify the
GSPN, which is dissected from the dura and fol-
lowed to where it enters under V3. A malleable
self-retaining retractor is placed as far deep as the
superior petrosal sinus to expose the petrous
ridge and retract the temporal dura superiorly.
The IAC location is now approximated using a
line bisecting the angle between the GSPN ante-
riorly and the AE (SSC) posteriorly. A 3-mm dia-
mond drill is used with a continuous
suction-irrigation system to expose the IAC. The
drilling starts medially close to the petrous ridge
and deepens inferiorly until the medial portion of
the IAC dura is identified. The drilling is contin-
ued laterally until we identify Bill’s bar, which
can serve as an important landmark for the facial
nerve at the lateral canal. Drilling continues
~270° around the IAC dura to provide a room for
maneuverability after dural opening. Care must
be taken not to open the cochlear angle just
anteromedial to the junction of the labyrinthine
facial segment and the GG or the vestibule, which
is located posterolateral to this lateral end of the
IAC (Fig. 11.5).Dural Opening and Tumor Dissection
Techniques
Once the IAC dura is exposed, it is incised along
its posterior length parallel to the superior ves-
tibular nerve to avoid injury to the facial nerve,
which lies in the anterosuperior portion of the
IAC. A facial nerve stimulation probe is used to
identify the location of the facial nerve in the lat-
eral portion of the IAC. A sharp hook is used to
transect the superior vestibular nerve just in the
posterior margin of Bill’s bar using very gentle
movement to protect the labyrinthine segment of
the facial nerve. The transverse crest at this lat-
eral aspect of the canal may prevent adequate
visualization of the cochlear nerve anteroinferi-
orly; however, when the dura of the IAC is
removed along the axis of the IAC posteriorly to11 Vestibular Schwannomas