133

Aneurysms of the Anterior Cerebral Artery: A, Segment

Aneurysms of the Anterior Cerebral Artery

General Aneurysms of the anterior cerebral artery
Considerations (ACA) deserve special consideration be-
cause of the diversity of their location,
complex anatomy, and critical character of
adjacent arteries and brain structures.
There are three principal sites for aneu-
rysms of the ACA: (1) proximal ACA (A,
segment); (2) anterior communicating ar-
tery (ACoA) complex; and (3) distal ACA
(pericallosal artery). The most common site
of origin is the ACoA complex, which is
generally approached by a pterional cranio-
tomy (see Chapter I).

We prefer the interhemispheric precal-
losal approach (see Chapter I) for the fol-
lowing: (1) ruptured ACA aneurysms
pointing directly anterior that may adhere
to the optic chiasm and (2) ACA aneurysms
unsuccessfully clipped by a pterional ap-
proach. Aneurysms of the pericallosal ar-
tery are next in frequency to those of the
ACA and are operated by the inter-
hemispheric callosal approach (see Chapter
I). Aneurysms of the proximal ACA seg-
ment (A, segment) are rare; a pterional ap-
proach is preferred.

Aneurysms of the Anterior Cerebral Artery:
a! Segment

2.78

134 Aneurysms of the Anterior Circulation

Special Aneurysms of the proximal ACA (A, seg-
Considerations ment) are rare, usually occurring in adoles-
cent and young women. Because these
aneurysms are frequently large, globular,
or fusiform, they are difficult to clip. With
the use of preoperative angiogram, the sur-
geon may assess the feasibility of perma-
nently trapping the aneurysm, which allows
both A₂ arteries and perforating arteries to
fill from the opposite ACA. The middle ce-
rebral artery and lateral perforating arteries
will fill from the ipsilateral internal carotid
artery.

Approach The patient is placed in the supine position
(see Chapter I). The pterional craniotomy is
modified to remove the frontal bone flush

with the orbital roof. If the frontal sinus is
opened, it should be obliterated by remov-
ing mucosa, packing with muscle, and seal-
ing with a pericrania! flap, which is rotated
from the frontal area and sutured to the
adjacent dura. Exposure of the subfrontal
anatomy is enhanced further by removing
cerebrospinal fluid, using a lumbar sub-
arachnoid catheter or ventricular drainage,
osmotic diuretics, and hyperventilation.
Adequate exposure can be difficult to
achieve after recent subarachnoid hemor-
rhages, particularly if cerebral edema, hy-
drocephalus, or a frontal hematoma is
present. Orbitozygomatic osteotomy (see
Chapter I) is an option that can enhance
exposure and reduce the need to retract the
frontal lobe; this adjunct is recommended
to approach giant ACA aneurysms.

2.79 Exposure begins by
placing I wo 15-mm retractors, the first on
the inferior surface of the frontal lobe and
the second on the anteromedial aspect
of the temporal lobe in the sylvian fissure.
The fissure is opened from a proximal ap-
proach through the carotid cistern. While
the frontal lobe is gently retracted, the sur-
geon patiently aspirates cerebrospinal fluid.
The arachnoid is cut sharply along the me-
dial aspect of the carotid artery until A, is
identified.

Aneurysms of the Anterior Cerebral Artery: A, Segment 135

ACA

(A, segment)

2.80

2.80 The retractor is moved
toward the junction of the olfactory tract
and the orbital surface of the frontal lobe.
Sharp dissection exposes the proximal A,
and the origin of a fusiform aneurysm.

2.81 Dissection of the arach-
noid continues across the aneurysm base
and the distal A, is identified.

136 Aneurysms of the Anterior Circulation

2.82 Temporary clips are
placed proximally and distally to isolate the
aneurysm, which is aspirated with a needle.

137

Anterior Cerebral Artery: A, Segment

2.83 The collapsed aneurysm
is dissected to ensure that all important per-
forators and the recurrent artery of Heub-
ner are excluded from both the entrapped
segment and the blades of the clips.

138 Aneurysms of the Anterior Circulation

2.84

2.84 Multiple fenestrated
clips can be used to reconstruct the artery
for fusiform aneurysms.

2.85 A right-angle fenes-
trated clip can be used to reconstruct the
artery for berry aneurysms of the A,
segment.

2.86 A clip graft can be used
to encase the weakened arterial segment.

2.86

2.85

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

Aneurysms of the Anterior Cerebral Artery: Anterior Communicating Artery (Pterional Approach) 139

Aneurysms of the Anterior Cerebral Artery:
Anterior Communicating Artery (Pterional
Approach)

Frontispiece

2.87

Special The anterior communicating artery (ACoA)
Considerations complex is the most common origin for an-
eurysms of the anterior cerebral artery
(ACA). Preoperative angiograms in multi-
ple views are reviewed to assess collateral
circulation, configuration, and orientation
of the aneurysm. A pterional approach (see
Chapter I) across the nondominant frontal
lobe is preferred unless anatomic consid-

erations direct the approach toward the
contralateral side. We prefer the inter-
hemispheric precallosal approach (see
Chapter I) for (1) ruptured ACoA aneu-
rysms pointing directly anterior that may
adhere to the optic chiasm, (2) ACoA aneu-
rysms unsuccessfully clipped by a pterional
approach, and (3) multiple aneurysms of
the ACoA and pericallosal artery.

140 Aneurysms of the Anterior Circulation

Posterior

communicating
artery

Optic nerve

Anterior

choroidal

artery

Anterior
cerebral
artery

Uncal
artery

2.88

Approach A pterional craniotomy is performed with
the patient in the supine position (see Chap-
ter 1). The pterional craniotomy is modified
to remove the frontal bone flush with the
orbital roof. If the frontal sinus is opened, it
should be obliterated by removing mucosa.
packing with muscle, and sealing with a
pericranial flap, which is rotated from the
frontal area and sutured to the adjacent
dura. Exposure of the subfrontal anatomy
is enhanced further by removing cere-
brospinal fluid, using a lumbar sub-
arachnoid catheter or ventricular drainage,
osmotic diuretics, and hyperventilation.
Adequate exposure can be difficult to
achieve after recent subarachnoid hemor-
rhages, particularly if cerebral edema, hy-
drocephalus, or a frontal hematoma is
present. Orbitozygomatic osteotomy (see
Chapter I) is an option that can enhance
exposure and reduce the need for retraction
of the frontal lobe; this adjunct is recom-
mended to approach giant aneurysms of the
ACA.

2.88 Exposure begins by
placing two 15-mm retractors, the first on
the inferior surface of the frontal lobe
and the second on the anteromedial aspect
of the temporal lobe in the sylvian fissure.
The fissure is opened from a proximal ap-
proach through the carotid cistern. While
the frontal lobe is gently retracted, the sur-
geon patiently aspirates cerebrospinal fluid.
The arachnoid is cut sharply along the me-
dial aspect of the carotid artery until A, is
identified.

2.89 The retractor is moved
forward along the frontal lobe as the chi-
asmatic cistern is opened along the anterior
border of the A, segment.

2.90 The arachnoid and tis-
sue of the gyrus rectus are coagulated in
preparation for exposing the ACoA region
medial to the olfactory tract. This dissec-
tion should remain subpial to protect the
aneurysm wall.

Aneurysms of the Anterior Cerebral Artery: Anterior Communicating Artery (Pterional Approach) 141

Lateral
striate
artery

2.89

142 Aneurysms of the Anterior Circulation

Recurrent
artery of
Heubner

Pia-arachnoid
overlying aneurysm

2.91

2.91, 2,92 The site of rupture is
covered by adherent pia-arachnoid, brain,
and clot (in the interhemispheric fissure)
and should not be disturbed. The left A,
segment is identified for contralateral prox-
imal vascular control. Sharp dissection is
used to develop a path for clip placement in
the junction formed by the aneurysm neck.
ACoA, and right (2.91) and left (2.92) A₂
segments.

Frequently, temporary occlusion of
both A, arteries is needed to reduce the
tension in large or complex aneurysms pri-
or to final dissection and clipping. This ma-
neuver is safe if systemic hypertension and
brain-protective anesthesia are used.

2.93 A 30-degree oblique clip
is guided into position across the neck of
the aneurysm.

2.94 The aneurysm dome is
punctured with a 22-gauge needle. Blood is
aspirated as the clip blades are closed.

Aneurysms of the Anterior Cerebral Artery: Anterior Communicating Artery (Pterional Approach) 143

2.93

t

2.94

L

144 Aneurysms of the Anterior Circulation

Medial hypothalamic
perforating artery

2.95

2.96

2.95, 2.96 The aneurysm and
clip are rotated so that the medial hypo-
thalamic perforators are shown to be free
from the clip blades. Irrigation and as-
piration of the interhemispheric clot are
performed. Final clip placement is con-
firmed by inspection or intraoperative
angiography.

Closure Closure is completed as for a standard
pterional craniotomy (see Chapter I).

---