288

Arteriovenous Malformations of the Brain

Infratentorial Convexity Arteriovenous
Malformations

General The majority of cerebellar arteriovenous
Considerations malformations (AVMs) present on the sur-
face of the cerebellar hemispheres and are
thus termed cerebellar convexity malfor-
mations. A few of these AVMs may extend
deep within the cerebellum or cerebellar
fissures to involve the brainstem or neuro-
vascular structures of the cerebellopontine
angle. These malformations vary in size
from small to large.

Most cerebellar convexity malforma-
tions are approached through a posterior
fossa craniotomy, but combination with a
transtentorial approach is occasionally re-
quired. Attention is directed to preserve
adequate venous drainage for the cerebellar
hemisphere and to document complete re-
moval of the malformation by intraopera-
tive angiography. An occipital burr hole
for emergency ventricular aspiration is
placed prior to closure because postopera-
tive swelling or hemorrhage can result in
sudden obstructive hydrocephalus.

289

Infratentorial Convexity Arteriovenous Malformations: Superior Cerebellar

Superior Cerebellar Convexity Arteriovenous
Malformations

4.94

Special AVMs located on the superolateral aspect
Considerations of the cerebellar convexity receive arterial
supply from branches of the superior cere-
bellar artery (SCA), anterior inferior cere-
bellar artery (AICA), and occasionally, pos-
terior inferior cerebellar arteries (PICAs).
Venous drainage is to vermian, superior
cerebellar, precentral cerebellar, superior
petrosal, basal, and mesencephalic veins;
these, in turn, enter the petrosal and trans-
verse sinuses.

The most common clinical presenta-
tion is hemorrhage, and in these cases, sur-
gical extirpation is preferred. In the ab-
sence of hemorrhage, patients with small
cerebellar convexity AVMs can be consid-
ered for stereotactic radiosurgery. To elimi-
nate deep feeding arteries, preoperative
embolization is considered for large or
complex malformations that extend into the
cerebellar peduncle and fourth ventricle.
The malformation illustrated in this section
occupies the superolateral portion (quad-
rangular lobule) of the cerebellum. A large
hematoma deep to the AVM penetrates to
the fourth ventricle and pons.

290

Arteriovenous Malformations of the Brain

Approach An upper lateral suboccipital craniotomy is
performed with the patient in the lateral
oblique position (see Chapter I). A femoral
artery sheath is placed prior to positioning
and maintained with heparin solution under
pressure. The skull is maintained in a radio-
lucent head-fixation device for intraopera-
tive angiography. An armored endotracheal
tube allows the neck to be flexed, facilitat-
ing exposure of the posterior fossa.

4.95 An upper lateral suboc-
cipital craniotomy is performed. The scalp
flap crosses the superior nuchal line and
descends in the midline. A superior and
lateral myofascial cuff is retained. The skin
and muscle flaps are reflected inferiorly.

The craniotomy is carried laterally to the
edge of the sigmoid sinus and superiorly to
the edge of the transverse sinus. A cruciate
incision is made in the dura after good cere-
bellar relaxation is achieved.

291

Infratentorial Convexity Arteriovenous Malformations: Superior Cerebellar

Tentorial
draining
veins

SCA

Precentral
cerebellar
vein

Perforating
arteries

Petrosal
PICA AICA vein

4.96

4.96 This illustration shows
the multiple sources of arterial blood sup-
ply, venous drainage, and location of the
malformation.

4.97 A I5-mm retractor de-
presses the cerebellar hemisphere. After bi-
polar coagulation, a pia-arachnoid incision
is made in cerebellar folia adjacent to the
malformation's posterior margin.

4.97

292 Arteriovenous Malformations of the Brain

4.98

4.98 One 10-mm retractor is
placed on the medial aspect of the hemi-
sphere while a 15-mm retractor elevates the
AVM toward the transverse sinus. The he-
matoma cavity is dissected free from gliotic
cerebellum.

4.99 The hematoma is com-
pletely removed. As the inferior and deep
aspects of the malformation are explored,
deep perforating arteries from the PICA
and lateral branches from the AICA are
coagulated and incised. The lateral border
of the malformation is further dissected
from the cerebellar folia.

4.99

Infratentorial Convexity Anenovenous Malformations: Superior Cerebellar 293

4.100

4.100 The superior retractor is
withdrawn and the malformation collapses
into the hematoma cavity. SC.A branches
and draining veins to precentral and ten-
torial veins are coagulated and incised.

4.101 Dissection proceeds lat-
erally along the malformation surface down
to the superior aspect of the pons and the
root entry of the trigeminal nerve. Numer-
ous branches of the SCA are coagulated
and incised, As dissection continues, prin-
cipal draining veins into the superior
petrosal sinus and tentorium are isolated.

4.101

294

Arteriovenous Malformations of the Brain

4.102 The superior petrosal
vein is coagulated and incised after the re-
maining arterial feeders from the AICA are
eliminated. The base of the cavity is in-
spected to document the complete removal
of the malformation and absence of small
bleeding sites. An intraoperative angiogram
is performed through the vertebral artery.

Closure Closure is performed as for an upper lateral
suboccipital craniotomy (see Chapter I).

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