94

Aneurysms of the Anterior Circulation

Aneurysms of the Ophthalmic Segment

General Considerations: Aneurysms can arise along the entire ophthalmic artery segment from the proximal
dural ring (where the internal carotid artery
[ICA] leaves the cavernous sinus) to the
origin of the posterior communicating ar-
tery. Aneurysms of the paraclinoid ICA
segment can expand the distal dural ring
where the ICA becomes extradural) and
create the illusion of an intracavernous ori-
gin. Carotid aneurysms in the region of the
ophthalmic artery may arise in the follow-
ing areas: adjacent to the ophthalmic artery
origin, lateral to the ophthalmic artery, or
juxtaophthalmic near the origin of the supe-
rior hypophyseal artery. Superior and me-
dially projecting aneurysms arise beneath
the optic nerve and anterior clinoid pro-
cess; these cause early optic nerve com-
pression that is characteristically asso-
ciated with a nasal-quadrant field cut.
Aneurysms related to the superior hypo-
physeal artery arise distal to the dural ring
and usually project posteriorly or laterally.
The optic chiasm is compressed when supe-
rior hypophyseal aneurysms become large,
which causes symptoms that mimic a pitu-
itary tumor.

Endovascular intra-aneurysmal bal-
loon placement, platinum coil placement,
or direct trapping procedures must be con-
sidered as alternative treatments. When
there are no medical or technical contrain-
dications to open surgery, especially in
cases of ruptured aneurysm, direct clipping
is the preferred approach.

If the surgeon anticipates occlusion of
the parent artery segment from which the
aneurysm arises, the patient must pass a
preoperative test by tolerating ICA occlu-
sion for 10 minutes. A transfemoral balloon
in the ICA occludes the intracranial ICA for
10 minutes while the awake patient continu-
ously undergoes neurologic and neuro-
physiologic monitoring, and a qualitative
or quantitative study of cerebral blood
flow. Provocative testing by decreasing
mean arterial pressure 30 percent below
resting baseline during temporary occlu-
sion is optional. Failure to tolerate occlu-
sion indicates the need for preoperative
extracranial-intracranial vascular bypass if
occlusion of the parent artery segment is
anticipated.

Complex aneurysms of the ophthalmic
artery region should be evaluated similarly
to those located in the cavernous sinus
(e.g., carotid challenge test, xenon flow
study, consideration for bypass). Definitive
treatment by balloon occlusion of the aneu-
rysm or carotid artery should be considered
as a therapeutic option.

Simple parophthalmic aneurysms that
point superiorly and arise distal to the distal
dural ring can be clipped easily by a pterio-
nal approach from either side (see Chapter
I). Because of their location, this type of
aneurysm may be clipped when found to be
incidental to contralateral lesions.

Aneurysms of the Internal Carotid Artery: Ophthalmic Segment 95

2.19

Special The ophthalmic segment aneurysm demon-
Considerations strated in this exercise has partial origin
along the paraclinoid ICA segment of the
anterior loop.

Approach The patient is placed in the supine position
(see Chapter I) with the head maintained at
30 degrees rotation to bring the surgeon's
line of view down the anterior clinoid proc-
ess. The skull is fixed in a radiolucent head-
fixation device to facilitate intraoperative
angiography. A pterional craniotomy is
modified to extend anteriorly to the mid-
point of the orbit flush with both the orbital
roof and the middle fossa floor. The exter-
nal and internal carotid arteries are exposed
in the neck for proximal vascular control
(see Aneurysms of the Intracavernous Car-
otid Artery, earlier in this chapter).

96

Aneurysms of the Anterior Circulation

2.20 After the dura is opened,
the brain is retracted and the arachnoid cis-
terns are opened. Aspiration of cerebrospi-
nal fluid enhances brain relaxation and
retraction. The dura is incised over the an-
terior clinoid process and the clinoid pro-
cess is removed.

2.21 Three flaps of dura are
elevated and retracted to expose the ante-
rior clinoid process. A high-speed pneuma-
tic drill with a diamond burr is used to
dissect and remove the clinoid process. The
tip of the process is disarticulated from its
attachment to the petroclinoid ligament.

I

97

Aneurysms of the Internal Carotid Artery: Ophthalmic Segment

2.22

Paraclinoid
segment
of ICA

Ophthalmic
artery ^/

Distal dura)
ring

2.23

2.22 The medial dura! flap is
reflected to expose the distal dural ring and
permit further dissection of the optic strut,
which exposes the full clinoidal segment of
the carotid artery.

2.23 An incision is made
through the medial dural flap across ihe
distal ring to expose the origin of the oph-
thalmic artery, the base of the medially di-
rected aneurysm, and the proximal dural
ring. A parallel incision is made in the optic
sheath to permit medial displacement of the
nerve.

98

Aneurysms of the Anterior Circulation

2.24 The optic nerve is re-
tracted medially. The 1C A is temporar-
ily occluded to decrease intra-aneurysmal
pressure. The aneurysm is punctured with a
22-gauge needle. While the aneurysm is as-
pirated, a right-angle fenestrated clip closes
the aneurysm base. Intraoperative an-
giography is performed to document the ef-
fective closure of the aneurysm and
preservation of patency of the ICA.

Closure The clinoid and sphenoid bones are sealed
with bone wax and covered with a
pericranial graft, which is held in place with
tissue adhesive. The remainder of the clo-
sure is done according to a standard pterio-
nal approach (see Chapter I).

99

Aneurysms of the 1C A: Posterior Communicating Artery and Anterior Choroidal Artery Region

Aneurysms of the Posterior Communicating
Artery and the Anterior Choroidal Artery Region

General Cerebral aneurysms frequently arise adja-
Considerations cent to the origin of the posterior communi-
cating artery (PCoA). The surgeon assesses
the preoperative angiography to determine
(1) whether the aneurysm neck is partially
obscured by the anterior clinoid process,
thus requiring clinoidectomy, and (2)
whether the PCoA is a fetal-type, filling the
posterior cerebral artery without collateral
branches from the basilar artery. Fetal
PCoAs must be preserved to avoid occipital
lobe infarction. Although short segments of
nonfetal PCoAs can be occluded to trap a
complex aneurysm, this step risks occlu-

sion of perforating arteries to the hypo-
thalamus (or internal capsule). Infundibular
widening of the origin of the PCoA is com-
mon and must be distinguished an-
giographically from a true aneurysm.

Cerebral aneurysms infrequently arise
adjacent to the origin of the anterior choroi-
dal artery. This artery must be skillfully
dissected free of the aneurysm and pre-
served. In approximately 15 percent of pa-
tients, sacrifice of the anterior choroidal
artery results in infarction of the internal
capsule with contralateral hemiplegia or
hemiparesis.

100

Aneurysms of the Anterior Circulation

Special An aneurysm of the PCoA is demonstrated
Considerations in this exercise. Although it is the most
frequently occurring aneurysm encoun-
tered by general vascular neurosurgeons,
these "easy" aneurysms should not lull
neurosurgeons into neglecting the basic
guidelines of aneurysm surgery.

Approach The patient is placed in a supine position
with the head maintained at 45 degrees ro-
tation. The craniotomy is pterional with a
half-and-half exposure of the frontal and
temporal lobes.

I

101

Aneurysms of the ICA: Posterior Communicating Artery and Anterior Choroidal Artery Region

2.27

2.26 After the dura is opened,
two 15-mm retractors are placed on the
frontal and temporal lobes. The veins to the
sphenoparietal sinus are coagulated and
incised.

2.27 The carotid cistern is
opened and gentle retraction elevates the
frontal lobe as cerebrospinal fluid is aspi-
rated. Aspiration of cerebrospinal fluid en-
hances brain relaxation and retraction. The
surgeon opens the proximal sylvian fissure.

Anterior
cerebral
artery

2.28

2.28 The arachnoid is opened
further to provide access to the proximal
carotid artery. The anterior temporal lobe is
retracted laterally to expose the base of the
aneurysm. The dome of the aneurysm
should remain undisturbed beneath the sur-
face of the temporal lobe or cerebellar
tentorium.

102

Aneurysms of the Anterior Circulation

2.29 The base of the aneu-
rysm is identified and dissected free from
the origin of the PCoA.

2.30

2.30 Adhesions are sharply
dissected to fully identify the base of the
aneurysm. The oculomotor nerve is identi-
fied deep to the aneurysmal base where it
frequently attaches to the dome.

Aneurysms of the ICA: Posterior Communicating Artery and Anterior Choroidal Artery Region 103

Anterior

choroidal

artery

2.32

2.31 A straight aneurysm
clip is guided into place along the previ-
ously dissected paths around the aneurysm
neck.

2.32 The aneurysm is punc-
tured with a 22-gauge needle and is aspi-
rated to document that its neck is
completely occluded.

105

Стр104 -Aneurysms of the ICA: Posterior Communicating Artery and Anterior Choroidal Artery Region

Anterior

Choroidal

artery

2.35

2.35 The aneurysmal sac is
rotated medially to show that no significant
aneurysm remains proximal to the clip. In-
traoperative angiography is seldom needed
when the anatomy of the aneurysm and ad-
jacent structures are clearly visualized.

Closure Closure is done according to a standard
pterional approach (see Chapter I).

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