212

Aneurysms of the Posterior Circulation

Aneurysms of the Vertebral Artery: Proximal to
the Posterior Inferior Cerebellar Artery
(Fusiform Dissecting)

3.71

Special Vertebral artery dissection usually begins
Considerations in the extradural vertebral artery and ex-
tends secondarily into the intradural space
where subarachnoid hemorrhage can oc-
cur. Aneurysms associated with arterial
dissection are usually pseudoaneurysms
with poorly formed walls and are not amen-
able to conventional clip placement. The
best tactic for clipping is placement of an
encircling clip over the segment of the ver-

tebral artery that contains the aneurysm, if
the posterior inferior cerebellar artery
(PICA) can be spared. The encircling clip
will protect the weakened segment but may
not prevent further distal dissection. Proxi-
mal trapping of the dissected segment
causes reversal of flow that may stop the
dissection and provides a valid therapeutic
option.

Aneurysms of the Vertebral Artery: Proximal to the Posterior Inferior Cerebellar Artery (Fusiform Dissecting) 213

Approach A lower lateral suboccipital craniotomy is
performed with the patient in the lateral
oblique position (see Chapter I).

Vertebral artery

Spinal accessory
nerve

3.73

3.72

3.72 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. Sharp dissection exposes the
vertebral artery as it enters the subdural
space.

3.73 A 2-mm retractor is
placed on the lateral medulla. Further dis-
section exposes the proximal vertebral ar-
tery at its junction with the aneurysmal
segment.

214 Aneurysms of the Posterior Circulation

3.74

3.74 The PICA origin is iden-
tified distal to the aneurysm segment.
Inspection shows a bluish discolored intra-
mural clot. The deformed artery is
unsuitable for conventional aneurysm
clipping.

3.75 Further dissection of
the aneurysmal lesion will permit a 5-mm
encircling clip to encase the weakened arte-
rial segment.

3.75

Aneurysms of the Vertebral Artery: Proximal to the Posterior Inferior Cerebellar Artery (Fusiform Dissecting) 215

3.76 Inspection shows that
the distal PICA origin and filaments of cra-
nial nerve XI have been spared. Micro-
Doppler scan will document persistent
blood flow through the arterial segment.

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

216

Aneurysms of the Posterior Circulation

Aneurysms of the Vertebral Artery: Posterior
Inferior Cerebellar Artery-Vertebral Junction

Considerations

bellar artery (PICA)-vertebral junction,
commonly called PICA aneurysms, arise
from the vertebral artery at the origin of the
PICA. The approach to these aneurysms
can be difficult because they are frequently
located ventral to the medulla and can be
entangled in the origin of the lower cranial
nerves (VI through XII). The exposure is

the rootlets of the cranial nerves. This ex-
posure gives the surgeon limited ability to
establish distal control of the vertebral
artery.

Aneurysms of the Vertebral Artery: Posterior Inferior Cerebellar Artery-Vertebral Junction 217

Approach A lower lateral suboccipital craniotomy is
performed with the patient in the lateral
oblique position (see Chapter I). If neces-
sary, this approach can be modified by re-
section of the medial one third of the
occipital condyle and lateral mass of Cl.

Hypoglossal
nerve

Vertebral
artery

Dentate
ligament

3.78

3.78 The dura is incised from
the upper cervical canal across the foramen
magnum along the outer aspect of the cere-
bellum and reflected laterally. Arachnoid of
the cisterna magna is incised and cere-
brospinal fluid is aspirated. The dentate lig-
ament is sectioned. The intradural segment
of the vertebral artery is identified and pre-
pared for proximal occlusion with tempor-
ary clips.

218

Aneurysms of the Posterior Circulation

Glossopharyngeal
nerve

Vagus
nerve

PICA

3.80

3.79

3.79

3./9 The PICA is traced
proximally to identify its junction with the
vertebral artery and the aneurysm base.

3.80 A microretractor ele-
vates the lower filaments of the vagus spi-
nal accessory nerves. Sharp dissection
identifies the space between the origin of
the PICA and the aneurysm base. Gentle
retraction is applied to the lateral medulla
to provide medial exposure of the aneu-
rysm base.

219

Aneurysms of the Vertebral Artery: Posterior Inferior Cerebellar Artery- Vertebral Junction

3.82

3.83

3.81 A slightly curved aneu-
rysm clip is guided into place along the
aneurysm base parallel to the axis of the
vertebral artery.

3.82 The aneurysm is aspi-
rated with a 22-gauge spinal needle, which
is inserted above the fibers of the vagus
nerve.

3.83 The collapsed aneurysm
sac and clip are rotated laterally and medi-
ally to allow inspection of the distal ver-
tebral artery and the PICA origin.

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

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