Aneurysms of the Basilar Terminus: Clinoidal 169

Aneurysms of the Basilar Terminus: Clinoidal

Special The majority of basilar terminus aneurysms

Considerations originate at the level of the posterior clinoid

process as seen on the lateral projection of

a cerebral angiogram. Aneurysms in this

¹ location can be approached by a standard

pterional craniotomy, an opening of the

proximal sylvian fissure, and a trajectory

between the internal carotid artery (ICA)

and the oculomotor nerve.

The temporal lobe should be mobilized
and retracted posteriorly and inferiorly.
The uncus is mobilized by incision of adhe-
sions along its medial margin; this allows
uncal retraction and improves visualization
of the distal basilar artery. Perforators aris-
ing from the P, posterior cerebral artery
(PCA) pass more directly backward to the
mesencephalon than those seen in supra-

17D

Aneurysms of the Posterior Circulation

clinoid basilar aneurysms. These perfora-
tors must be dissected downward to
prepare a path to safely place the aneurysm
clip.

Approach A pterional craniotomy is performed with
the patient in the supine position with the
head rotated 30 degrees and placed in ex-
tension. A radiolucent head-fixation device
is used in preparation for intraoperative
angiography. A lumbar spinal catheter is
inserted prior to positioning for intraoper-
ative aspiration of cerebrospinal fluid. An-
esthesia must be prepared to provide
cerebral protection if temporary trapping is
needed.

Optic

nerve

Carotid
cistern

3.11

3.11 After the dura is
opened, two 15-mm retractors are placed
on the frontal and temporal lobes. The syl-
vian fissure and carotid cistern are widely
opened to expose the ICA and interpedun-
cular cistern. Cerebrospinal fluid is aspi-
rated gradually to increase brain relaxation

and facilitate exposure. Bridging veins
between the temporal tip and sphenoparie-
tal sinus are coagulated and incised. The
frontal lobe is elevated and the temporal
lobe is retracted downward and posteriorly.

171

Aneurysms of the Basilar Terminus: Clinoidal

Oculomotor
nerve

3.12

1

3.12 The membrane of Lille-
quist is incised and cerebrospinal fluid is
further aspirated from the interpeduncular
cistern.

3.13 The 1CA is retracted
medially to expose the posterior communi-
cating artery (PCoA) and its perforating
branches, aneurysm base, and P, segments.

PCoA

Mesencephalic perforating
arteries

3.13

172 Aneurysms of the Posterior Circulation

173

Aneurysms of the Basilar Terminus: Clinoidal

3.14 The PCoA is retracted
medially. Sharp dissection separates the
filmy arachnoid adhesions between the an-
eurysm base and the contralateral proximal
P, segment of the PC A.

3.15 Dissection of the aneu-
rysm neck and the ipsilateral proximal P,
segment completes the path for clip
application.

3.16 A straight aneurysm
clip is applied from an inferior to a superior
trajectory.

174

Aneurysms of the Posterior Circulation

3.17

3.17 The clip is closed and
the dome of the aneurysm is aspirated with
a 22-gauge spinal needle.

3.18 The aneurysm sac and
the clip are tilted inferiorly. This step en-
ables the surgeon to inspect the base of the
aneurysm and to document that perforating
vessels and proximal P, segments are free
of the clip blades.

3.18

Closure Closure is performed as for a pterional cra-
niotomy (see Chapter I).

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