220

Aneurysms of the Posterior Circulation

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

3.84

Special Aneurysms arising on the distal branches of
Considerations the posterior inferior cerebellar artery
(PICA) may descend into the upper cervical
spine, where they lie in an extracranial lo-
cation. Failure to visualize both PIC As in
the process of angiography may result in
failure to disclose the source of sub-
arachnoid hemorrhage. Reflux down the
vertebral artery from the contralateral in-
jection may not always reach this distal lo-

cation. Direct clipping is the preferred
treatment for aneurysms of the distal PICA.
Occasionally trapping of the aneurysm
(owing to a fusiform configuration) may be
required. The aneurysm's exact location in
relation to the regional vascular anatomy
and bony structures is assessed to deter-
mine the appropriate level of exposure.

221

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

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

3.85 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 cerebro-
spinal fluid is aspirated. The intradural seg-
ment of the vertebral artery is identified and
prepared for proximal occlusion with tem-
porary clips. A 15-mm retractor is placed
on the cerebellar tonsil to expose the proxi-
mal tonsilar hemispheric branch of the
PICA. The aneurysm base is visualized be-
neath a filament of the spinal accessory
nerve.

Distal PICA

Dentate ligament

Spinal accessory
\ nerve

3.85

222 Aneurysms of the Posterior Circulation

Hypoglossal
nerve

3.86

3.86 Adhesions between the
distal PICA and the vertebral artery are
sharply dissected. The aneurysm dome re-
mains attached to the lateral aspect of the
medulla.

3.87 The base of the aneu-
rysm is defined proximal and distal to its
origin on the PICA and dissected free from
filaments of the spinal accessory nerve.

C1 nerve
root

3.87

Aneurysms of the Vertebral Artery: Aneurysms of the Distal Posterior Inferior Cerebellar Artery 223

3.88

3.89

3.88 A right-angle fen-
estrated clip (3 mm) is placed across the
base of the aneurysm parallel to the axis of
the parent artery.

3.89 The dome of the aneu-
rysm is aspirated with a 22-gauge spinal
needle.

224 Aneurysms of the Posterior Circulation

3.90

Lateral

medullary

artery

3.90 The collapsed dome re-
mains embedded in the wall of the medulla
and adherent to a prominent medullary
artery.

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

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