105views. Intraoperative neuromonitoring of cranial
nerves 5, 7, 8 (Auditory Brain Responses (ABR)),
and 11 is established. For larger tumors, somato-
sensory and motor-evoked potentials may also be
monitored. Tumors with adjacent brainstem
edema are usually not completely resectable due
to the obscured pial-tumor interface. We have
tried to move away from the routine use of a lum-
bar drain. A preoperative lumbar spinal tap for
drainage of 30 mL of cerebrospinal fluid (CSF) is
one option for decompression. The image guid-
ance reference arc should be positioned anterior
to the surgical field. After image registration, the
position of the transverse-sigmoid sinus junction
is marked on the scalp. A C-shaped incision is
marked behind the ear using the top of the pinna
and mastoid tip as the superior and inferior end
points. The skin flap is dissected subcutaneously
and rotated forward over the ear. Then the fascia
over the mastoid process is incised with electro-
cautery from near the tip superiorly to the base of
the mastoid process and then posteriorly along
the superior nuchal line. The posterior aspect of
the temporalis muscle is dissected subperiosteally
forward and the suboccipital muscles posteriorly
and inferiorly. Initially a self-retaining retractor is
used but after the soft tissue dissection can be
replaced by scalp hooks so as not to interfere with
access to the operative field once under the
microscope.
Once the soft tissue dissection is complete,
image guidance is used to select burr hole posi-
tioning, and then a small craniotomy or craniec-
tomy is completed exposing the inferior surface
of the transverse sinus and the posterior surface of
the sigmoid sinus. The mastoid emissary vein is a
good landmark to follow toward the sigmoid
sinus as it is posterior to the sinus. It can be iso-
lated by removing the surrounding bone and can
be coagulated and cut close to the sigmoid sinus,
or it can be left in a bony canal up to the back
edge of the sinus. Care must be taken to not use a
volume of bone wax so as not to stuff in too much
wax sufficient to encroach upon the lumen of the
sigmoid sinus and thus cause thrombosis. In addi-
tion to bone wax, excessive use of any hemostatic
agent, including liquid ones, can also lead to sinus
thrombosis, so these should be avoided as well.
If bleeding is encountered, a simple Gelfoam
placed over the sinus followed by a cotton patty
should be sufficient to control bleeding without
thrombosing the sinus. We typically avoid the
“extended retrosigmoid approach” advocated by
others [ 14 ] due to our experience with two cases
of intraoperative sinus thrombosis and cerebellar
swelling. During the standard retrosigmoid
approach, opening the dura toward the foramen
magnum and subsequently opening the cisterna
magna arachnoid allow for drainage of CSF, cer-
ebellar relaxation, and exposure of the tumor.
There are some nuances for each location,
which will be covered below based on an experi-
ence of over 115 cases.APFMThese tumors reside high and anteriorly in the
CPA, and we perform suprameatal drilling in
nearly every case to facilitate exposure of their
base of attachment. It is our practice to do these
cases with our neuro-otologists who perform the
drilling. The removal of this bone is completed
using a combination of round cutting and dia-
mond burrs. The bone is removed over the mid-
portion internal auditory canal until the dura is
exposed to delimit the inferior portion of the dis-
section, and the bone is progressively removed
superiorly. The subarcuate artery is drilled
through and controlled with bone wax or drilling
and can be taken without adverse sequelae.
Posterolaterally, care must be taken to not enter
the superior semicircular canal. Medially the dis-
section may be continued until the entry of the
trigeminal nerve or tumor is clearly seen into
Meckel’s cave. Removal of this bone carries with
it the advantage of removing a common site of
the attachment of the meningioma to its dural
base, which may devascularize the tumor and
simplify further dissection. We typically preserve
the superior petrosal vein when possible. The
fifth nerve is usually displaced superiorly and
medially to the tumor. Larger tumors have vari-
able extension into Meckel’s cave. While
ultrasonic aspirators are efficient at tumor deb-
ulking, their size can pose a problem due to the8 Meningiomas of the Cerebellopontine Angle