Aneurysms of the Basilar Terminus: Giant Infraclinoidal 175

Aneurysms of the Basilar Terminus:
Giant Infraclinoidal

Special Basilar terminus aneurysms with a neck
Considerations arising below the level of the posterior
clinoid process have been considered low-
lying. Conventional pterional approaches
through the sylvian fissure risk poor visual-
ization of the proximal basilar artery as well
as of the proximal aneurysm neck. Per-
forating arteries arising on the posterior
basilar terminus and the P, segment of the
posterior cerebral artery (PCA) are likewise
poorly visualized and are at greater risk of
occlusion. Infraclinoidal basilar aneurysms

are best operated by subtemporal ap-
proach. To avoid significant temporal lobe
retraction, orbitozygomatic osteotomy and
inferior mobilization of the temporalis mus-
cle may be a valuable adjunct. If the neck of
the aneurysm lies between the base of the
posterior clinoid process and the level of
the internal auditory canal, an anterior
petrosectomy or incision of the tentorium
cerebelli is necessary to create an expanded
view into the upper posterior fossa.

176 Aneurysms of the Posterior Circulation

Giant Aneurysms

Particular techniques are needed for giant
aneurysms: adequate exposure for clipping,
aspiration of intraluminal clot, and dissec-
tion that spares the perforators of P, and P₂.
and the terminal branches of the distal basi-
lar artery. The perforators project up to-
ward the mesencephalon and may adhere to
the back wall of the aneurvsm. Therefore, a
direct lateral trajectory is needed to visual-
ize this anatomy. Retraction or partial sec-
tion of the tentorium cerebelli (and occa-
sionally resection of the anterior temporal
lobe) may be advisable to gain the needed
exposure.

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. A catheter is placed
in the femoral artery in preparation for in-
traoperative angiography. A temporal cra-
niotomy is performed (see Chapter I: Sub-
temporal Approach).

3.20 The dura is incised and
reflected inferiorly. Cerebrospinal fluid is
aspirated from the lumbar catheter to im-
prove relaxation of the temporal lobe. Two
15-mm retractors are placed on the inferior
temporal gyrus and slowly elevated. The
mesencephalic cistern is opened and cere-
brospinal fluid is continuously aspirated.
Arachnoid dissection shows the oculomo-
tor nerve, P, segment of the PCA, and dis-
tal basilar artery. A portion of the dome and
base of a giant, partially thrombosed aneu-
rysm is exposed.

Aneurysm

segment)

3.20

Aneurysms of the Basilar Terminus: Giant Infraclinoidal 177

Superior cerebellar
artery (SCA)

PCoA

PCA

(P₂ segment)

3.21

Oculomotor
nerve

3.22

3.21 ' Two metallic clips are
placed on the posterior communicating ar-
tery (PCoA) distal to its perforators, adja-
cent to the P| segment. The PCoA is incised
between the clips.

3.22 A 2-mm microretractor
is used to retract the medial edge of the
tentorium cerebelli and the oculomotor
nerve. This maneuver exposes the distal
basilar artery, its major branches, and the
base of the aneurysm.

178 Aneurysms of the Posterior Circulation

Pressure
cuff

3.23

3.24

3.23 A femoral catheter is in-
serted and, with the aid of image fluo-
roscopy, the right vertebral artery is
cannulated. A pressure cuff is attached to
heparinized isotonic saline solution to
maintain patency of the catheter.

3.24 Guided by image fluo-
roscopy, the neuroradiologist manipulates
a microballoon catheter into the distal basi-
lar artery.

Aneurysms of the Basilar Terminus: Giant Infraclinoidal 179

r

3.25

3.25 The tip of the micro-
catheter is visible in proper position at the
basilar terminus. An incision is made in the
dome of the thrombosed aneurysm with a
scalpel.

180 Aneurysms of the Posterior Circulation

Viable

aneurysm

sac

3.26

3.27

3.26 An ultrasonic aspirator
is used to evacuate the organized thrombus
from the lumen of the aneurysm. The wall
of the viable aneurysm sac, which lies at
the base of the thrombus, is not penetrated
until the tracker balloon catheter is inflated.
Then, the remainder of the thrombus is as-
pirated to fully collapse the aneurysm sac.

3.27 With the balloon in-
flated, complete arrest of flow into the an-
eurysm is achieved. The base of the
aneurysm can be manipulated. Perforators
can be dissected free from the base in order
to clear a path for the application of the
clip. The primary clip is placed across the
aneurysm base; clip application is facili-
tated by collapsing the dome and mobilizing
the perforators.

181

Aneurysms of the Basilar Terminus: Giant Infraclinoidal

3.28

3.28 A reinforcing clip is
placed over the first clip to increase the
closing force.

3.29

3.29 The reinforcing clip is
placed near the distal end of the primary
clip blades to maximize closing force. The
primary clip blades must be perfectly posi-
tioned in the feet of the reinforcing clip to
avoid torsion of the primary clip. Perfora-
tors at the distal basilar artery from the
proximal P, segments are inspected and
shown to be free of the clip blades.

182

Aneurysms of the Posterior Circulation

3.30 The tracker balloon
catheter is deflated. The aneurysm dome is
reinspected and the orifice of the aneurysm
is shown to be completely obliterated. In-
traoperative angiography is performed to
document the patency of the distal basilar
artery and its distal branches.

3.30

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

Aneurysms of the Distal Posterior Cerebral Artery 183

Aneurysms of the Distal Posterior
Cerebral Artery

3.31

General Distal aneurysms of the posterior cerebral
Considerations artery (PCA) are those arising along the P₂
and occasionally P₃ segments of the PCA.
These aneurysms, as well as those of the
superior cerebellar artery (SCA), are best
exposed by a subtemporal approach (see
Chapter I).

down to the level of the facial nerve. Tem-
porary trapping of the aneurysm by proxi-
mal and distal placement of low-pressure
clips facilitates dissection of the sac and
precise clip placement.

Special Anterior petrosectomy is an option for low-
Considerations lying aneurysms because it provides addi-
tional exposure below the trigeminal nerve

184 Aneurysms of the Posterior Circulation

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. A catheter is placed in
the femoral artery in preparation for intra-
operative angiography. A temporal cranio-
tomy is performed (see Chapter 1: Sub-
temporal Approach). The craniotomy may
be modified by addition of an anterior pe-
trosectomy.

Trochlear
nerve

Medial posterior
choroidal artery

Peduncular

arterial

branches

Inferior

temporal

artery

3.32

3.32 The dura is incised and
reflected inferiorly. Cerebrospinal fluid is
aspirated from the lumbar catheter to im-
prove relaxation of the temporal lobe. Two
15-mm retractors are placed on the inferior
temporal gyrus and slowly elevated. The P₂
segment of the PCA is identified at its junc-
tion with the posterior communicating ar-
tery. The P₂ segment is followed distally
until the aneurysm base and distal branches

of the PCA are identified. Temporary clips
are placed on the proximal PCA adjacent to
the aneurysm and on the distal PCA arterial
branches (inferior temporal and occipital
arteries). The base of the aneurysm is dis-
sected from its attachment to the mesen-
cephalic and basal veins in preparation for
clip placement.

185

Aneurysms of the Distal Posterior Cerebral Artery

3.33

3.33 A right-angle clip is
placed parallel to the axis of the parent
artery and the aneurysm base. The dome of
the aneurysm is aspirated with a 22-gauge
spinal needle and the temporary clips are
removed. The aneurysm and clip are ro-
tated inferiorly to document that perforat-
ing vessels to the mesencephalon are free of
the clip blades.

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

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