186 Aneurysms of the Posterior Circulation

3.34

General Aneurysms of the superior cerebellar artery

Consideration (SCA) take their origin at the junction of the

SCA and the basilar artery. A more distal

location on the SCA rarely occurs. These

aneurysms, like those arising from the dis-

tal posterior cerebral artery (PCA), are ex-
posed by the subtemporal approach (see
Chapter I).

187

Aneurysms of the Superior Cerebellar Artery

Special An anterior petrosectomy may be needed
Considerations to improve the exposure for aneurysms of
the SCA. Retraction or section of the ten-
torium cerebelli effectively exposes most of
these lesions. Proximal control of the basi-
lar artery should be obtainable by either
temporary clipping or intravascular balloon
techniques. Oculomotor nerve rootlets are
often draped over the dome and may need
to be freed bv dissection.

Approach The patient is placed in the supine position
after a catheter is placed in the lumbar
spine for cerebrospinal fluid drainage. The
patient's right shoulder is elevated with a
gelatin pad. The head is rotated until the
sagittal suture is oriented parallel to the
floor. The cranium is fixed in a radiolucent
skull-fixation device and a catheter is
placed in the femoral artery in preparation
for intraoperative angiography. A temporal

craniotomy is performed (see Chapter I:
Subtemporal Approach). The craniotomy
may be modified by additional anterior
petrosectomy.The dura is incised and re-
flected interiorly. Cerebrospinal fluid is as-
pirated from the lumbar catheter to
improve relaxation of the temporal lobe.
Two 15-mm retractors are placed on the
inferior temporal gyrus and slowly
elevated.

3.35 The mesencephalic cis-
tern is opened by sharp incision of the
arachnoid. Aspiration of cerebrospinal fluid
permits additional relaxation of the tempo-
ral lobe. The medial edge of the tentorium
cerebelli is retracted laterally and main-
tained with a suture. The trochlear nerve is
identified posterior to its insertion in the
free edge of the tentorium.

3.35

188 Aneurysms of the Posterior Circulation

3.36 The membrane of Lille-
quist is incised to expose the P, segment of
the PC A.

3.36

189

Aneurysms of the Superior Cerebellar Artery

4

Medial
posterior
choroidal
artery

Thalamoperforating
arteries

Posterior

communicating

artery

3.37

I*
I

3.37 The oculomotor nerve
is displaced laterally by a microsuction
while the aneurysm base is dissected free
from the proximal segment of the PCA.

3.38 A 1-mm microretractor
displaces the oculomotor nerve medially.
The filmy arachnoid adhesions are sepa-
rated from the basilar trunk, proximal SCA,
and aneurysm base.

190 Aneurysms of the Posterior Circulation

3.39

3.40

191

Aneurysms of the Superior Cerebellar Artery

3.39 A slender right-angle
clip is guided underneath the oculomotor
nerve and across the base of the aneurysm.

3.40 The dome of the aneu-
rysm is aspirated with a 22-gauge spinal
needle.

3.41 The aneurysm base and
clip are rotated anteriorly to document that
the superior mesencephalic branches of the
SCA are free of the clip blades.

il

Superior

mesencephalic

arteries

3.41

Closure Closure is performed as for a subtemporal
craniotomy (see Chapter I).

192

Aneurysms of the Posterior Circulation

Aneurysms of the Midbasilar Trunk

General Aneurysms of the midbasilar trunk take
Considerations their origin in the region of the anterior
inferior cerebellar arteries (AICAs). This
region is relatively inaccesible from above
by subtemporal approach and from below
by suboccipital approach. If the angiogram
shows a definable aneurysm neck with sev-
eral millimeters of space between the aneu-
rysm and the AICAs or perforating arteries,
the surgeon may consider endovascular in-
tra-aneurysmal occlusion by balloon or
thrombogenic substance or trapping of a
short segment of the basilar artery. The
four-vessel angiogram is analyzed to deter-
mine if one or both posterior communicat-
ing arteries will continue to perfuse the
basilar artery and its branches above the
level of any planned occlusion.

Contrast-enhanced computed tomo-
graphic (CT) or magnetic resonance imag-
ing (MRI) scans are useful to assess the
exact location of the aneurysm in relation
to the petroclival anatomy. Midbasilar an-
eurysms generally originate between the
levels of the trigeminal and the facial
nerves. High midbasilar aneurysms can be
exposed by a subtemporal approach with
the modification of anterior petrosectomy
or a petrosal approach (i.e., temporal crani-
otomy, suboccipital craniotomy, posterior
petrosectomy). For most midbasilar aneu-
rysms the options for direct exposure in-
clude posterior petrosectomy and lower
lateral suboccipital craniotomy (see Chap-
ter 1). Mid-basilar and low-basilar aneu-
rysms are approached through the space
between the auditory-facial and glossopha-
ryngeal nerve complexes.

---