Child’s Brain 10: 121-129 (1983)

Giant Arteriovenous Aneurysm of the Posterior Fossa in
a Three-Month-Old Infant
Edgardo Schijman, Jorge A. Mortges
Division of Neurosurgery. Hospital de Niños, Buenos Aires. Argentina

Key Words. Angiography • Arteriovenous aneurysm ■Computed tomography •
Hydrocephalus - Posterior fossa tumors • Thrombosis
Abstract. A 3-month-old female infant presented a 20-day history of drowsiness and
maturing deterioration. The neurological exam showed peripheric facial palsy on the right
side and a brachiocrural hemiparesis on the left. A brain scan revealed a lesion of avascular
content in the posterior fossa. The computed tomography scan showed hydrocephalus and a
high-density lesion, nonenhanced after introduction of the contrast agent, compatible with a
clot at posterior fossa level. Likewise, after contrast new images appeared which had not been
seen previously, considered as afferent and efferent vascular elements to the lesion. The cere­
bral angiography showed an avascular lesion in the cerebellar vermis with important hyperthrophy of arterial and venous elements, although no stea phenomena of neighbouring areas
was evident. These findings, and the absence of cardiac failure, suggested the diagnosis,
confirmed by surgery, of giant clotted arteriovenous malformation. The patient has done well
postoperalively.

Introduction

C> 1983 S. Kargcr AG. Basel
0302-2803/83/0102-0121 S 2.75 0

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Vascular malformations are one of the most interesting problems in
neurosurgery. The polymorfism of its clinical pattern, the need for careful
programming and analysis of the diagnostic procedures and the frequent
complexity of its surgical treatment, require the neurosurgeon’s maximum
judgement and skill. Classically, arteriovenous malformations are divided
into angiomatous and fistulous types, which depends on whether or not
they disclose a capillary network between the arterial and venous territo­
ries. The fistulous malformations which are less frequent than the angiom­
atous ones [2, 3] can be of traumatic, infectious or congenital origin [12],

Fig. 1. Initial unconlrastedCT scan showing a high-density mass in the vermis and both
cerebellar hemispheres.

While carotid-cavernous fistulas are the most common in adults, fistulas
of the vertebral or vertebral and carotid arteries with the vein of Galen are
the most common in children. Less frequent presentations are internal
carotid, vertebral or superficial temporal artery fistulas with their satellite
veins at extracranial level or abnormal communications between branches
of the internal carotid, external carotid or vertebral artery at intracranial
level, with superficial or deep cerebral veins or with dural sinuses.
An unusual case of intracranial hypertension is presented here,
produced by a giant arteriovenous aneurysm in the posterior fossa, which
was completely clotted. The interesting neurological findings are discussed
and comments on the good results obtained by surgery are made.

Our patieni is a 3-month-old girl who refused feeding and presented drowsiness 20 days
before admission. A few days later her parents noticed lagophthalmos on the right and devi­
ation to the left of the bucal commissure. The neurological examination revealed a drowsy

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Case Report

Fig. 2. Contrast-enhanced CT scan discloses a vascular area at the anterior part of the

patient with slight retardation, inability to hold her head up or to follow objects with her eyes.
Head circumference was 43 cm, which was normal for her age: normotense fontanelle. right
peripheric facial palsy and minimal left brachiocrural hemiparesis. Discs were normal. Nega­
tive cranial auscultation and normal cardiovascular and respiratory exam.
The skull X-ray revealed incipient splitting of sutures. The EEC was normal. A brain
scan with technetium-99 showed a tumoral mass in the posterior fossa with high uptake in
the periphery showing an annular shaped image. The uncontrasted computed tomography
(CTj scan (fig. I) showed a great tumoral mass in the vermis and both cerebellar hemispheres,
more extended towards the right, hyperdense, 21-44 EMI units, with no perilesional edema.
The contrast substance (fig. 2) caused the appearance of apparently vascular images which
were not visible in the noncontrastcd exam, in the front and left part of the tumor, which did
not modify its initial densities. An important hydrocephalus secondary to obstruction of the
fourth ventricle was also observed.
A right ventricular-peritoneal shunt was inserted at first, to take care of the hydro­
cephalus. to which the patient’s depression was attributed. Despite this shunt procedure, the
patient did not improve and some days later developed respiratory and swallowing difficulties
attributed to the fact that the low cranial nerves had been affected.
Owing to the unusual tomographic patterns of this lesion a cerebral angiography by
brachial route was done (fig. 3, 4) which revealed the ventricular dilation and an expanded
avascular lesion in the posterior fossa with important hypertrophy of the vertebrobasilar and
right superior cerebellar arteries, which appeared to llow into a vascular lake which is already

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mass.

Schijman/Mongcs

124

observed in the arterial phase and still persists in the venous phase, situated in the foremost
and lower part of the avascular area. The vascular drainage was done via a very dilated vein
ending in the vein of Galen. Surgery1was done with the patient in brow' down position and
a midline approach of the posterior fossa, which allowed the total removal of a large ancurismatic sac; thick-w'alled. nonpulsating, measuring approximately 4 x 3 x 2 cm. and
completely thrombosed (fig. 5, 6). As a first step the right superior cerebellar artery, of about
3-4 mm in diameter, which ran to the forward right face of the sac. was clipped, and two
efferent thick veins were ligated: one can be observed in the preoperative angiography, and
another not revealed in that study which ran horizontally towards the left, to the lateral sinus.
The pathology revealed an afferent artery and efferent veins of normal appearance, although
they showed hypertrophied walls, whilst the aneurysmatic sac presented the replacement of
the vascular normal histo-architecturc by a connective wall. The intraluminal clot was of the
mixed type although there was fibrinoid predominance and no evidence of organization.
The patient evolved well in spite of a difficult postoperative period. The control angiog­
raphy done selectively by femoral route 3 months later revealed the disappearance of the avas­
cular area, better irrigation of the cerebellar parenchyma compared with the preoperative
study, the persistence of the hypertrophied vertebrobasilar system, the partial involution of
the afferent artery and the total involution of the efferent veins.

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Fig. 3. Cerebral angiography shows an avascular cerebellar mass with hypertrophy of
the vertebrobasilar and right superior cerebellar artery.

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125

Fig. 4. Venous phase of the angiography shows the venous drainage of the lesion.

At present. 3 years after surgery, the patient’s progress is good, with slight retardation,
convergent strabismus and slight peripheric facial paresis, both on the right side.

The cerebral arteriovenous malformations present in different forms.
While the angiomatous lesions usually present as a subarachnoid or intra-

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Discussion

Scliij man Monges

126

parenchimatous hemorrhage [2, 6, 11, 13], fistulous lesions appear
initially by cardiac failure, intracranial hypertension or by the combina­
tion of both, associated or not with intracranial bruits [10]. Less frequently,
both types of malformation can present as epileptic seizures of Jacksonian
type, transient ischemic attacks, focal progressive neurological deficit, etc.

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Fig. 5. External aspect of the partially open aneurysmal sac.
Fig. 6. Internal aspect of the sac. Note the nonhomogcnous conformation of the clot.

127

[2], While the carotid-cavernous fistula is predominant in adults, the most
common fistula in infancy is the abnormal communication between
branches of the vertebral or vertebral and carotid arteries with the vein of
Galen which causes a secondary dilation of the latter. In this type of
malformation, four different clinical pictures have been described: (1)
decompensated cardiac failure with intracranial bruit in newborn infants;
(2) moderate cardiac failure with macrocephaly and intracranial bruit in
3- to 6-month-old infants; (3) macrocephaly and intracranial bruit with no
cardiac signs in children between 6 months and 3 years old, and (4)
subarachnoid hemorrhage, intracranial hypertension or psychomotor
retardation, with or without syncopal episodes or intracranial bruits in
older children, adolescents, or adults [1]. Dean [4] recommends the consid­
eration of a fifth form of presentation: an intracranial hypertension
syndrome with no bruits and without cardiac signs owing to the fact that
the aneurysm has clotted. Our patient presented a picture of intracranial
hypertension because of hydrocephalus secondary to obstruction of the
fourth ventricle by the malformation, as well as signs of compression, of
the right side of the pons with right peripheric facial palsy and left brachiocrural hemiparesis, but at no moment presented symptoms or signs of
cardiac failure with increased cardiac output such as is observed in these
types of arteriovenous malformation when they appear at this age [8, 14,
18], The cause of cardiac failure is the great increase of the venous return
to the right atrium by the decrease of the peripheric resistance owing to the
abnormal communication between arterial and venous elements through
which can circulate up to 90% of the cardiac output.
Heinz et al. [7] explain the absence of cardiac symptomatology as the
result of the intrasacular thrombosis in pre-natal form or during the birth
itself. On the other hand, the cases of Lazar [9] and Six et al. [16] did not
have cardiac signs either, but in both, the clot had a laminated structure
with aged areas and others of more recent formation. Our patient did not
present symptoms or signs of cardiac failure either, in spite of the fact that
the thrombosis of the malformation was relatively recent: owing to the
absence of granulation tissue, it can be assumed that the clot was not more
than 10 or 15 days old.
The cranial X-ray only showed nonspecific signs of intracranial hyper­
tension. The chronic hypertension at aneurysmatic sac level can account
for its calcification, although this is rare before 15 years of age [17]; the
incidence ofcalcification is higher, nevertheless, in clotted cases. The brain
scan revealed an increased uptake of the radionucleid in ring form because

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Giant Arteriovenous Aneurysm

128

of the wall of the aneurysmatic sac, the altered surrounding tissue, or
because of both situations simultaneously; sometimes and when it exists,
the cause of this high uptake is attributed to the granulation tissue of the
clot. The center of the lesion without high uptake on the brain scan made
us suppose at that moment that we were dealing with a probable cystic
astrocytoma ofthe cerebellum. TheCT scan findings are interesting as they
deal with an initially hyperdense lesion, although with uneven densities in
its interior and without enhancement after injecting the contrast agent,
compatible with a blood clot. This contrast agent revealed new images on
CT, not observed before, corresponding to elements with free circulating
blood which were afferent and efferent to the lesion. It was considered
without free circulating blood inside in view of the absence of enhance­
ment after contrast injection. Six et al. [16] say that clotted malformations
show a peripheric enhancement after contrast material owing to the gran­
ulation tissue which exists at the level of the wall of the sac, which is a
phenomenon already observed before by the same author in cerebral arte­
rial aneurysms [15], Furthermore, he has seen, as in our case, the existence
of uneven blood densities within the lesion and the absence of perilesional
edema. His case, a clotted arteriovenous aneurysm of the vein of Galen,
had a density o f40 EMI units, whilst ours revealed a density o f2 1^14 EMI
units. Usually, clotted blood, with about 90% hematocrit, presents an
average density of40 EMI units and free circulating blood, with about 45%
hematocrit, an average density of 18-20 EMI units. The case of Dean [4]
showed, as the previous one, a hyperdense image with evident ring form
enhancement after contrast. Amacher et al. [2] reported a similar case to
ours (case 1of their series), in a 9-year-old patient with intracranial hyper­
tension evidenced by headaches with papilledema and splitting of sutures;
the CT revealed a mass lesion in the left cerebellar hemisphere, and the
angiography showed hydrocephalus with a cut off vessel at lesion level,
which turned out to be a clotted ‘venous angioma’ [2],
According to Epstein et al. [5] we emphasize the indication of angiog­
raphy when the tomographic image does not coincide, as in our case, with
the findings usually observed in tumors of the posterior fossa.
Summarizing, this is an arteriovenous fistula which did not produce
cardiac failure, but did produce a secondary aneurysmatic venous dilation,
with a high-density image on the uncontrasted CT scan due to a recently
formed clot. For this reason, furthermore, it did not fill in the angiography
and did not present signs of steal in the vertebral and carotid territories
either.

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Schijman / Monges

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Dr. Edgardo Schijman, Hospital de Niños. División Neurocirugía,
Gallo 1330, (1425) Buenos Aires (Argentina)

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