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sigmoid sinuses. CSF is then carefully aspirated
from the adjacent cisterns to allow for a relaxed
cerebellar hemisphere. Taking a little extra time
to remove CSF at this point will make the rest of
the procedure proceed much easier and decrease
the chance of retraction injury to the cerebellum.
For surface lesions, en bloc resection should pro-
ceed after identification of tumor boundaries,
often with the help of registered neuronaviga-
tional systems.
Patient positioning in retrosigmoid approaches
may be modified depending on tumor location.
Modified supine positions may be appropriate for
far anterior lesions bordering the cerebellopon-
tine angle and brainstem. In these approaches,
the patient is positioned supine, with a large roll
placed under the shoulder on the same side as the
lesion. The patient is thus rotated away from the
neurosurgeon, and the head may be further
rotated approximately 45° to the contralateral
side. Depending on surgeon preference and
tumor size, the skin incision may be positioned
linearly over or slightly lateral to the mastoid
notch, following a path beginning 5 cm superior
and terminating 4 cm inferior to the notch. Other
surgeons may prefer a C-shaped incision begin-
ning 2 cm above the ear, proceeding to its vertex
at the mastoid notch and terminating 2 cm poste-
rior to the pinna. The craniotomy can be planned
following a similar arc; the transverse sinus may
be used as the upper border and the mastoid pro-
cess as the lower border (Fig. 13.6c). Mastoid air
cells exposed during the procedure should be
plugged with bone wax. After bone flap removal,
the dura is divided, exposing the lateral border of
the cerebellar hemisphere. Once again, aspiration
of CSF from the cerebellopontine angle cistern is
key to obtaining relaxation of the cerebellum,
which is then progressively and gently retracted
posteriorly using small cottonoids, exposing the
lateralized or anteriorly extending tumor.
Superior Cerebellar Approach
Far anterior or superior cerebellar lesions can be
accessed by modifying the standard suboccipital
craniotomy via a supracerebellar, infratentorial
approach. A vertical, linear incision is made 2 cm
above the inion and extending 6–8 cm below the
inion. The preferred craniotomy in these cases
extends from above the torcula superiorly to just
above or including the foramen magnum inferi-
orly. Upon bone flap removal and dural opening,
the tentorium may be gently retracted superiorly,
allowing clear visualization of the tentorial sur-
face of the cerebellum. Resection of the tumor
can then proceed according to best practices out-
lined below. This approach can be moved pro-
gressively further lateral, allowing greater access
to more anterior lesions. A transtentorial dissec-
tion after occipital craniotomy may provide bet-
ter viewing of the cerebellar peduncles and
anterosuperior anatomy of the posterior fossa.
These approaches should employ stereotactic
navigation to aid in tumor resection and defini-
tion of acceptable boundaries of resection.Excision of Metastatic Lesions
The technique for excision of metastatic lesions
is an important consideration. The senior author
favors an en bloc resection whenever possible.
This minimizes disruption to the tumor body and
at least theoretically reduces the incidence of
local and regional recurrence [ 55 , 56 ]. Dissection
just outside of the glial pseudocapsule of the
tumor allows for excellent hemostatic control of
interfacing and feeding vessels and provides the
surgeon with an opportunity for thorough
GTR. Some tumors may be too large for en bloc
resection, and an ultrasonic aspirator may be
used initially to debulk the tumor in these cases.
The gliotic pseudocapsule should be targeted
thereafter, ensuring a safe and efficient resec-
tion. Recent retrospective analyses have exam-
ined the extent to which resection technique
influences leptomeningeal disease (LMD) after
posterior fossa metastasis as well as local and
regional tumor recurrence. LMD is a known risk
after resection of metastases to the posterior
fossa [ 57 – 61 ] and confers a shortened survival
time and dismal prognosis once discovered. Suki
and colleagues discovered that piecemeal tumor
resection was associated with a significantlyB.D. Weaver and R.L. Jensen