147catheter are placed, and pillows are positioned
between the legs. For all surgeries in the posterior
fossa, we use a total intravenous anesthesia tech-
nique. The benefits of this have been described
elsewhere [ 5 ]. The patient is given corticoste-
roids, antibiotics, and mannitol for brain
relaxation.
The incision used is a gently curved incision
of one to two fingerbreadths behind the mastoid.
The course of the transverse and sigmoid junc-
tion and transverse and sigmoid sinuses can be
anticipated based on the bony anatomy. A straight
line is drawn between the roots of the zygoma to
the inion, and the transverse sinus lies along this
line. It curves inferiorly into the sigmoid sinus at
the region of the asterion. The incision is infil-
trated with lidocaine and opened with a sharp
blade. After self-retaining retractors are placed,
we attempt to identify the region of the mastoid
emissary vein, which is a guide to the location of
the sigmoid sinus. Bleeding from the mastoid
emissary is controlled with bone wax. We per-
form either a craniectomy or a craniotomy,
located just below the transverse sigmoid junc-
tion at its most superior extent. We look to iden-
tify the inferior aspect of the transverse sinus and
the posterior aspect of the sigmoid sinus along
the course after the bone flap is removed. This
ensures an adequate trajectory and maximal visu-
alization of the CPA. A roughly 2- to 3-cm oval
opening is made extending from the transverse
sinus down along the posterior aspect of the sig-
moid sinus. The dura is usually opened in a cruci-
ate fashion that allows the flap to be reflected
superiorly or laterally along the transverse and
sigmoid sinuses, respectively. Alternatively, a
cuff of dura may be left adjacent, and the opening
may follow the sinuses. This allows the cuff to be
reflected with sutures for added retraction. After
the dura is opened, we bring the operating micro-
scope in the field and identify the superior and
lateral aspects of the cerebellum. We then con-
tinue our dissection down along the petrous ridge
at its junction with the tentorium and identify the
petrosal vein. The arachnoid is opened in this
location to allow egress of cerebrospinal fluid
(CSF). Immediately inferior to the petrosal sinus,
we look for evidence of the VS.
Upon visualization of the tumor, the outer layer
of arachnoid is reflected down to expose the poste-
rior aspect of the tumor. We use soft cottonoids to
reflect the arachnoid and the vasculature from the
tumor and expose the tumor to develop the win-
dow for resection. We immediately stimulate the
back of the tumor to see if there is an aberrant loca-
tion of the facial nerve. At this time, we use a dis-
sector and identify the IAC. The cuff of dura over
the IAC is opened approximately 1–2 cm, and the
lateral aspect of the IAC is drilled to enable visual-
ization of the limits of tumor within the canal. This
then enables identification of the location of the
facial nerve early in the dissection. If the facial
nerve is running along the anterior aspect of the
tumor as in the vast majority of cases, a window is
opened in the posterior aspect of the tumor, and a
specimen is removed for pathological analysis. WeFig. 11.1 (continued) Images showing steps of a retrosi-
gmoid approach for resection of a left small VS. Axial CT
brain cuts without contrast (a) and with contrast (b) dem-
onstrating medially located VS. (c) Preoperative BAEP
responses demonstrate symmetric hearing. (d) Skin inci-
sion. (e) A 2.5-cm-diameter craniectomy is performed
exposing the transverse and sigmoid sinuses. (f) Dural
opening along the margins of the transverse and sigmoid
junction. (g) IAC drilling intradural. (h) Sealing of the
opened air cells using bone wax after IAC exposure is
completed. (i) Dura is opened over the medial aspect of
the tumor. (j) The posterior aspect of the tumor exposure
and a window is cut after verifying the facial nerve is not
located on the posterior aspect of the tumor. (k) The ultra-
sonic aspirator is used to debulk the center of the tumor.
(l) The tumor capsule is gently elevated from the cerebel-
lum and brainstem, and the facial and vestibulocochlear
nerves are located at their brainstem exit and entry,
respectively. (m) Continued dissection of the capsule
from the facial and vestibulocochlear nerves. We carefully
use soft cottonoids to protect the nerves during the dissec-
tion. (n) The tumor has been removed and the facial nerve
is stimulated at the brainstem to verify continuity. (o) The
region of the IAC that was drilled is coated with bone wax
to prevent any possibility for CSF leak. (p) Fat graft is
placed over the drilled IAC and fibrin glue is applied. (q)
Large bur hole cover is used to cover craniectomy defect.
(r) Postoperative BAER demonstrates preserved hearing.
(s, t) Postoperative CT in the coronal and axial planes
demonstrating region of bone drilling and tumor removal11 Vestibular Schwannomas