168
Surgical Approach
After general anesthesia induction and patient
intubation, the patient is positioned in a lateral
decubitus position with the head held in a three-
point fixation head clamp. Muscle paralytic
agents are avoided, and neuromonitoring—
including motor evoked and somatosensory
evoked potentials, facial nerve and auditory
brainstem evoked responses, and 9th, 10th,
11th, and 12th cranial nerve monitoring—is
used routinely in these cases. The head is kept
in a neutral position with slight lateral neck flex-
ion toward the contralateral shoulder so that the
mastoid tip is at the highest point in the surgical
field. An axillary roll is placed under the depen-
dent side; the ipsilateral shoulder is slightly
flexed, and the arm is pulled down and secured
with a tape over a bellow or an arm support fixed
in the operating table. Undue traction of the
ipsilateral shoulder and arm should be avoided
to prevent brachial plexus injury. The operat-
ing table is reflexed, and the patient is secured
onto the operating table using an adhesive tape
for airplane positioning during the surgery. The
pressure points are checked and padded appro-
priately. Neurophysiological baseline studies
are obtained after positioning is complete so that
undue traction of the brachial plexus or neck
lateral flexion is detected and readjusted before
starting the procedure. A neuronavigation sys-
tem can be used to help localize the position of
the skin incision and the bony removal in rela-
tion to the sigmoid and transverse sinuses.
Anatomically, a straight line connecting the
ipsilateral root of the zygoma and the inion along
the superior nuchal line is a landmark for the ipsi-
lateral transverse sinus. The asterion is located
4 cm posterior to the ipsilateral external auditory
meatus and can usually be felt as a bony depres-
sion just superior and posterior to the mastoid
notch. This point marks the inferior margin of the
sigmoid-transverse sinus junction. A line extend-
ing from the asterion inferiorly just posterior to
the mastoid tip marks the posterior margin of the
sigmoid sinus. A curved skin incision is planned
0.5–1 cm posterior to the mastoid notch so that
one third is above and two thirds are below the
asterion. The hair above the ipsilateral pinna is
clipped and draped in case a subtemporal bony
window is necessary for resection of the supra-
tentorial part of the lesion.
Once the skin incision and the bony exposure
are complete, a small craniotomy or craniectomy
is performed. It is very important to expose the
posterior third of the sigmoid sinus and the infe-
rior third of the transverse sinus to be able to
reflect the dural edges or leaflet and to see along
the posterior petrous and the inferior tentorial
surface without difficulties. In cases where
hydrocephalus is present on preoperative imag-
ing, a preoperative or intraoperative frontal or
occipitoparietal external ventricular drain may be
inserted and used to relax the brain during the
surgery and to prevent postoperative CSF leak.
The dura is opened in a cruciate fashion or curved
along the inferior sinus border leaving a small
cuff of dura for watertight closure at the end. The
dural margins are tacked up superiorly and ante-
riorly over the sinuses margins using dural
stitches. Under microscopic vision, the prepon-
tine and/or the pontomedullary cistern arachnoid
membrane is opened sharply, and CSF is allowed
to egress to aid cerebellar relaxation. The cyst
should be visible at this stage, and the arachnoid
membrane covering the cyst is dissected sharply
A small, self-retaining retractor with a brain spat-
ula may be used with minimal retraction over the
lateral part of the cerebellum to allow better visu-
alization. Care must be taken not to cause traction
injury of the seventh and eighth cranial nerves or
petrosal veins during this stage. The seventh and
eighth nerve complex should be identified early.
Attempts should be made to preserve all petrosal
veins, but in certain cases, some petrosal veins
may have to be sacrificed to prevent accidental
tears or to provide better visualization for the
deeper portion of the CPA cistern. At this stage,
the cyst contents are debulked using careful
microdissection techniques. It is important to
remember that the cranial nerves and posterior
circulation blood vessels and the perforators may
be embedded within or displaced by the cyst and
should be preserved at all costs. Careful attention
to the abducens and trochlear nerves is important
because these two nerves are small and can beG. Alzhrani and W.T. Couldwell