246 252


246

Arteriovenous Malformations of the Brain


Supratentorial Deep Brain
Arteriovenous Malformations

General Supratentorial deep brain arteriovenous
Considerations malformations (AVMs) differ from convex-
ity malformations in location, presentation,
and complexity of removal. These AVMs
occupy the substance of the deep white
matter, including the corona radiata, inter-
nal capsule, corpus callosum, basal ganglia,
and thalamus. For purposes of illustration,
we consider these lesions in four catego-
ries: callosal, medial temporal, caudo-
thalamic, and posterior thalamostriate.
These deep brain malformations, except for
medial temporal AVMs, are more likely to
present with neurologic deficit due to par-
enchymal hemorrhage than with headache
or epilepsy. Deep brain malformations are
located in eloquent brain, drain to the deep
venous system, and vary in size but are
usually small to medium. Their clinical
grades, according to Spetzler's classifica-
tion, reflect an associated increased risk of
morbidity if treated with surgical resection
when compared with convexity malfor-
mations. Alternative therapies, such as ob-
servation and radiosurgery, should be
considered.

The subcortical location of deep brain
AVMs requires the development of surgical
corridors that avoid injury to critical corti-
cal areas or white matter tracts. Magnetic
resonance imaging is helpful in defining the
relationship of the malformation nidus to
deep brain structures. Guidance tech-
niques, such as ultrasound and stereotaxis,
are useful adjuncts to surgical localization.
Once the AVM is identified at surgery, em-
phasis is focused on developing a corridor
around the malformation to reach the arte-
rial feeders, which are usually obscured on
the undersurface of the malformation. Pre-
operative embolization, application of laser
energy to the nidus, and other strategies
must be available to achieve surgical resec-
tion with an acceptable level of morbidity.


Supratentorial Deep Brain Arteriovenous Malformations: Callosal 247

Callosal Arteriovenous Malformations


0x01 graphic


Special Arteriovenous malformations (AVMs) of
Considerations the medial frontal hemisphere are found
along the entire length of the corpus cal-
losum from anterior to posterior and can
extend distal to the callosum in the medial
occipital lobe. Malformations in this loca-
tion are referred to as callosal or cingulate
AVMs. Most callosal AVMs are small or
medium in size, receiving arterial supply
from the ipsilateral A2, callosal marginal,
and pericallosal arteries. Large callosal
AVMs receive additional arterial supply
from the contralateral anterior cerebral
and ipsilateral middle cerebral arterial
branches. Venous drainage is both superfi-
cial and deep. Superficial venous drainage
is to the superior sagittal sinus and along
the corpus callosum to the inferior sagittal
sinus. Deep venous drainage is to subepen-
dymal veins of the ventricular system,
which in turn enter the internal cerebral

veins. Hydrocephalus can develop owing to
obstruction of the foramen of Monro by an
enlarged subependymal vein.

Callosal AVMs usually present with
hemorrhage. A hemorrhagic presentation
in combination with surgical accessibility
through the interhemispheric space gener-
ally leads to a preference for surgical extir-
pation rather than observation or radio-
surgery.


I


248

Arteriovenous Malformations of the Brain


Approach This section illustrates the approach to a
mid-callosal AVM
with a large hematoma
in
the cingulate gyrus posterior to the mal-
formation. A unilateral parasagittal crani-
otomy is made with the patient in the
supine position (see Chapter I, Inter-
hemispheric Approach: Callosal). The head
is maintained in a radiolucent head-fixation
device for intraoperative angiography. We

prefer to place the lesion side down with
the sagittal suture parallel to the floor; how-
ever, forehead-up is an acceptable alterna-
tive. A femoral artery catheter sheath is
placed preoperatively and maintained with
a pressurized heparin solution. A lumbar
catheter for intraoperative cerebrospinal
fluid drainage placed prior to positioning
facilitates brain relaxation and retraction.


0x01 graphic

4.28


Supratentorial Deep Brain Arteriovenous Malformations: Callosal 249


0x01 graphic

Draining
vein

Callosal
marginal
arteries

4.29

4.28 A sagittal view of the
malformation depicts the arterial supply
from the pericallosal and callosal marginal
arteries. Venous drainage terminates in the
sagittal sinus and internal cerebral vein. A
hematoma is located in the cingulate gyrus,
corpus callosum, and lateral ventricle.

4.29 The medial aspect of the
cranial flap is sited on the edge of the sagit-
tal sinus. The dural flap is reflected medi-
ally to cover the sagittal sinus. Two
retractors are placed on the medial aspect
of
the hemisphere, anterior to the major
draining vein. An anterior cerebral vein en-
tering the sagittal sinus has been dissected
from its arachnoidal attachment to permit
wider retraction of the hemisphere. The
arachnoid is opened over
the corpus cal-
losum to identify the course of the draining
vein on the cingulate gyrus and pericallosal
arteries.

4.30 A third retractor blade
is placed on the medial edge of the falx. The
cortex is opened over the cingulate gyrus
adjacent to branches entering the draining
\ein. Dissection begins on the superior bor-
der of the malformation.


0x01 graphic

4.30


250

Arteriovenous Malformations of the Brain


0x01 graphic

4.31

Callosal
marginal
artery


4.31 The draining vein is re-
tracted medially to increase exposure of the
margins of the AVM. Several feeding
branches from the callosal marginal artery
are coagulated and
cut.


0x01 graphic

4.32 A 2-mm retractor en-
larges the exposure. The hematoma is aspi-
rated from the cingulate gyrus and medial
white matter.


251

Supratentorial Deep Brain Arteriovenous Malformations: Callosal


0x01 graphic

4.33

4.33 The malformation is re-
flected medially as deep perforating arteries
are coagulated.

4.34 The malformation is re-
flected laterally to expose the remaining
branches from the pericallosal artery; these
branches are coagulated and incised. Atten-
tion is directed anteriorly where a second-
ary draining vein penetrates the corpus
callosum to empty into the septal veins.
This vein is coagulated at the border of the
lateral ventricle.


0x01 graphic

Pericallosal
artery

4.34


i


252

Arteriovenous Malformations of the Brain


4.35 The malformation is lifted
from the corpus callosum and suspended
by its superficial vein draining to the supe-
rior sagittal sinus, which is then coagulated
and incised. Its bed is inspected for residual
AVM and bleeding from perforating sub-
ependymal arteries. The opening
into the
lateral ventricle is explored for residual
hematoma.

Intraoperative angiography is per-
formed prior to closure. It is advisable in
most circumstances to evaluate both ante-
rior cerebral arteries to ensure that elimina-
tion of bilateral arterial supply is complete.


0x01 graphic

Callosal
marginal
artery

Subependymal

perforating

arteries

Draining
vein

Lateral
ventricle


4.35

Closure Closure is performed as for a parasagittal
craniotomy (see Chapter I, Interhemispher-
ic Approach: Callosal).



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