202

Aneurysms of the Posterior Circulation

Aneurysms of the Vertebrobasilar Junction

3.58

General Aneurysms of the proximal basilar artery
Considerations and vertebrobasilar junction pose signifi-
cant problems of accessibility. These
aneurysms are frequently large with com-
plex configuration. They are inaccessible
through the middle fossa except when as-
sociated with marked elongation and tor-
tuosity of the vessels. These aneurysms lie
ventral to the brainstem and medial to

the cranial nerves. We recommend consid-
eration of endovascular intra-aneurysmal
occlusion by balloon, thrombogenic sub-
stance, or endovascular trapping proce-
dures when the site of aneurysm origin is
unencumbered by branching vessels. The
options for a direct surgical approach in-
clude a lower lateral suboccipital cra-
niotomy (see Chapter I) and midface
approaches.

203

Aneurysms of the Vertebrobasilar Junction

Special The vertebrobasilar junction aneurysm in
Considerations this exercise is operated by lower lateral
suboccipitai approach. The difficulties en-
countered with this approach include the
development of adequate exposure lateral
to the brainstem, the need to work between
the rootlets of the lower cranial nerves, the
ability to gain control of the contralateral
vertebral artery, and (he establishment of
distal vascular control on the proximal basi-
lar artery. Additional lateral exposure can
be obtained by posterior petrosectomy or
by removal of the medial one third of the
occipital condyle (see Chapter I).

Approach A lower lateral suboccipitai craniotomy is
performed with the patient in the lateral
oblique position (see Chapter I). If the need
for intraoperative angiography is antici-
pated, the head will be maintained in a ra-
diolucent head fixation device; a femoral
artery sheath will be inserted prior to posi-
tioning and maintained by injecting pres-
surized heparin solution. Auditory brain-
stem and somatosensory evoked potentials
are monitored throughout the procedure as
a relative indicator of brainstem ischemia.
Anesthesia is prepared to administer cere-
bral protective agents if temporary occlu-
sion of the basilar artery is used.

Glossopharyngeal
nerve

Vagus nerve

Spinal accessory
nerve

Posterior
inferior
cerebellar
artery

3.59

3.59 The dura is incised from
the foramen magnum along the outer aspect
of the cerebellum and reflected laterally. A
10-mm retractor is placed on the outer as-
pect of the cerebellar tonsil at its junction
with the lower medulla. The arachnoid of
the cisterna magna is incised and cere-
brospinal fluid is aspirated. A 2-mm retrac-
tor is placed on the flocculus (near the
lateral foramen of the fourth ventricle or
foramen of Luschka) to expose the lower
cranial nerves and the proximal vertebral
artery.

204

Aneurysms of the Posterior Circulation

3.60

3.60 A 1-mm self-retaining
retractor displaces the lower cranial nerves
downward. The 2-mm retractor is directed
upward to mobilize the medulla from the
vertebrobasilar junction. The arachnoid
overlying the basilar artery is incised.

3.61 The base of the aneu-
rysm is exposed by gently increasing re-
traction on the medulla. The arachnoid
adhesions are separated from the aneurysm
base and the contralateral vertebral artery.

205

Aneurysms of the Vertebrobasilar Junction

Anterior

spinal

artery

3.62

3.62 The arachnoid adhe-
sions and anterior spinal artery are sepa-
rated from the base of the aneurysm to
prepare a path for clip application.

3:63 An oblique-angle clip is
guided into the narrow space beneath the
medulla across the aneurysm base.

3.63

206 Aneurysms of the Posterior Circulation

3.64

3.64 The clip blades are ap-
proximated and the aneurysm is aspirated
with a 22-gauge spinal needle.

3.65

3.65 The aneurysm dome is
rotated to document that the anterior spinal
artery is free of the clip blades.

Closure Closure is performed as for a lower lateral
suboccipital craniotomy (see Chapter I).

207

Aneurysms of the Vertebral Artery

Aneurysms of the Vertebral Artery

General Vertebral artery aneurysms generally lie
Considerations within the cerebral spinal fluid cistern of
the cerebellopontine angle. They can take
origin distal to the junction of the posterior
inferior cerebellar artery (PICA) with the
vertebral artery or, more commonly, arise
at the PICA-vertebral artery junction.

Vertebral artery aneurysms proximal
to the PICA may be fusiform in configura-
tion. These aneurysms are sometimes asso-
ciated with spontaneous dissection of the
vertebral artery. This dissecting aneurysm
has been recognized with greater frequency
as a source of subarachnoid hemorrhage.
The angiographic pattern of focal vaso-
spasm with post-stenotic fusiform dilata-
tion, associated with subarachnoid he-
morrhage, is a common presentation of in-
tradural vertebral artery dissection.

PICA-vertebral artery aneurysms
arise from the vertebral artery at its junc-
tion with the PICA. The approach to these
aneurysms is complicated by their origin,
which is frequently ventral to the medulla
and entangled within the origin of cranial
nerves IX through XII (occasionally VII
and VIII). Options to direct surgical clip-
ping include intra-aneurysmal occlusion
with balloon or thrombogenic device. Trap-
ping procedures may be performed if the
patient's tolerance to unilateral vertebral
artery occlusion is documented pre-
operatively and final balloon placement
does not interfere with circulation to the
brainstem. Tolerance to occlusion is as-
sessed by neurologic examination during a
10-minute balloon occlusion since because
is no satisfactory method to measure brain-
stem cerebral perfusion.

a Iff

208

Aneurysms of the Posterior Circulation

Aneurysms of the Vertebral Artery: Distal to
the Posterior Inferior Cerebellar Artery

3.66

Considerations

PICA origin may be located ventral to the
brainstem and are difficult to adequately
expose. Posterior petrosectomy can sup-
plement the lower lateral suboccipital ap-
proach (see Chapter I) to give the surgeon a
better view ventral to the brainstem. The
majority of vertebral aneurysms distal to
the PICA can be approached by lower lat-
eral suboccipital craniotomy; the approach
in this exercise includes the option of par-
tial resection of the occipital condyle and
lateral mass of the first cervical vertebra

tion of the vertebral artery medially, a m;
neuver that provides a far lateral approac
to the ventrolateral medulla.

209

Aneurysms of the Vertebral Artery: Distal to the Posterior Inferior Cerebellar Artery

Approach A lower lateral suboccipital craniotomy and
partial resection of the medial third of the
occipital condyle and lateral mass of the
first Cl are performed with the patient in
the lateral oblique position (see Chapter I).
If the need for intraoperative angiography
is anticipated, the head is maintained in a
radiolucent head-fixation device and a fem-
oral artery sheath is inserted prior to posi-

tioning and maintained by pressurized
heparin solution. Auditory-brainstem and
somatosensory evoked potentials are mon-
itored throughout the procedure as a rela-
tive indicator of brainstem ischemia. The
anesthesia team is prepared to administer
cerebral protective agents if a temporary
trapping maneuver (focal hypotension) is
used.

Extradural

vertebral

artery

Spinal

accessory

nerve

Hypoglossal
nerve

3.67

3.67 The dura is incised from
the upper cervical canal across the foramen
magnum, along the outer aspect of the cere-
bellum, and reflected laterally. A 15-mm
retractor is placed on the lateral aspect of
the cerebellar tonsil at its junction with the
lower medulla. The arachnoid of the cister-
na magna is incised and cerebrospinal fluid
is aspirated. A 2-mm retractor is placed on
the flocculus (near the lateral foramen of
the fourth ventricle) to expose the lower
cranial nerves and the proximal vertebral
artery. The origin of the PICA is identified
proximal to the fusiform aneurysm and re-
tracted laterally with a microretractor.

210 Aneurysms of the Posterior Circulation

3.68 A straight aneurysm
clip is applied across the vertebral artery
proximal to the fusiform aneurysm and dis-
tal to the origin of the PICA.

3.69 The microretractor is
adjusted so that cranial nerves IX and X are
displaced downward. Dissection exposes
the distal extent of the fusiform aneurysm.

Facial and
vestibulocochlear
nerve complex

Glossopharyngeal
nerve

Vagus nerve

~t——Spinal accessory
/ nerve

PICA

3.69

Aneurysms of the Vertebral Artery: Distal to the Posterior Inferior Cerebellar Artery 211

3.70 An angled aneurysm
clip is placed to effectively trap the aneu-
rysm at the site of previous subarachnoid
hemorrhage.

Closure Closure is performed as for a lower lateral
suboccipital craniotomy (see Chapter I).

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