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Imaging Finding
Multiplanar MRI of
the foetus was subsequently performed on a GE -Echospeed 1.5 T MR, single
shot fast spin echo (ssFSE) sequence, TE of 92, TR of 1370, Nex (no. of
excitations) of 0.55, Field of view 38 x 26 cm and matrix 256 x 224. It
showed a large S-shaped area of flow void along the course of the vein
[Figure - 1]. The straight and transverse sinuses were also enlarged [Figure
- 2].
Diagnosis
Vein of Galen aneurysmal
malformation
There was no hyperintense signal within these dilated structures to suggest
thrombosis. The rest of the brain parenchyma and ventricles were normal.
No other abnormal tortuous vessels were found. MR venography was not done
as the patient was unable to cooperate further.
Pregnancy continued uneventfully and the child was born at 35 weeks' gestation.
Post-natal digital subtraction angiography [DSA] corroborated the findings
[Figure - 5]. Glue embolisation was subsequently done, with successful
obliteration of the malformation. However, the child died at 29 hours
of age from intractable congestive heart failure.
Discussion
Vein of Galen aneurysmal
malformations (VGAM) are rare congenital vascular malformations characterised
by shunting of the arterial flow into an enlarged cerebral vein dorsal
to the tectum. Most of these malformations present in early childhood,
often causing congestive heart failure in the neonate.
VGAM is defined as an aneurysmal dilatation of the vein of Galen, with
arterial input from one or more major intracranial arteries, either directly
or via an interposed angiomatous malformation. Arteriovenous malformations
arise when fistulas develop in positions where primitive vessels cross
in the embryo, which is most prominent near the choroid plexus. Fistula
formation in the deep midline region, therefore, results in a malformation
consisting predominantly of the choroidal vessels drained by the deep
venous system, of which the vein of Galen is the main channel.
Although VGAMs constitute only 1% of all cerebral vascular malformations,
they comprise up to 30% of all paediatric vascular malformations. VGAM
develops between the 6th and the 11th week of gestation, after the development
of the circle of Willis. Other venous anomalies such as anomalous dural
sinuses and sinus stenoses are commonly present in association with VGAM.
A fully developed vein of Galen malformation may vary considerably in
complexity from an aneurysmal dilatation fed by the branches of posterior
choroidal or posterior cerebral vessels, to an extremely complex malformation
fed by all major intracranial vessels. Antenatal MRI can show the malformation
in three dimensions and depict the exact anatomy of the dilated channels
and thrombosis if any. Magnetic resonance angiography (MRA) with 2D-TOF
may be a useful additional technique for evaluating foetal VGAM.
Embolisation of the feeding arteries is the preferred therapeutic modality
for a patient with severe cardiac failure. MRI is mandatory before endoarterial
treatment, to assess the brain parenchyma. If there is severe parenchymal
damage, endovascular treatment cannot compensate for the irreversible
melting-brain process. MRI has a prognostic value, allowing the decision
for therapeutic approach. Angiography is mandatory only at the time of
endovascular treatment, while MRA and MRI have a role in follow-up.
Antenatal USG and
Colour Doppler can make the diagnosis of VGAM; however, MRI can not only
make the diagnosis but also evaluate any associated parenchymal damage
and thrombosis to a better extent, because of excellent soft-tissue contrast
and lack of interference by bony structures. In conclusion, MR imaging
and MR angiography can indicate the major vessels of supply, tortuousity
of accessible arteries, venous anatomy, and parenchymal / ventricular
status even antenatally and aid in the management and follow-up of such
lesions.
References
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2. Johnston IH, Whittle IR, Besser M, Morgan MK. Vein of Galen Malformation:
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3. Kothari SS, Naik N, Juneja
R, Saxena A. Aneurysm of the Vein of Galen in neonates: Report of Four
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Dr Sona Pungavkar, MRI Centre, Nanavati Hospital, Mumbai.
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