Vein of Galen Aneurysmal Malformation

KEY FACTS

Terminology

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Vein of Galen aneurysmal malformation (VGAM) is deep cerebral arteriovenous fistula

Imaging

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Elongated midline cystic structure
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  Extends from area behind 3rd ventricle posteriorly toward occiput
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  Drains via straight sinus or superior sagittal sinus
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Flow on color Doppler with arterialized venous flow on pulsed wave tracing
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Other brain findings include both destructive (e.g., porencephaly) or developmental (e.g., migrational) lesions
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Serial US utilized to evaluate for developing hydrops or intracranial parenchymal damage

Top Differential Diagnoses

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Arachnoid cyst: May have similar grayscale appearance but no flow on color Doppler

Clinical Issues

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Up to 80% of fetal cardiac output may be diverted to cerebral circulation
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Presence of any associated finding confers poor outcome
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  High mortality; survivors with neurologic or cardiac impairment
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  Most common associated findings include cardiomegaly (66.7%) and ventriculomegaly (38.9%)
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  Even mild cardiomegaly correlated with poor outcome
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Better prognosis for isolated VGAM without other findings
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At birth, vascular shunt usually increases
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  Cessation of flow to low-resistance placenta

Scanning Tips

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Always use color and pulsed Doppler for any cystic-appearing brain mass
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Perform detailed views of brain parenchyma
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  High-flow state “steals” blood from surrounding developing brain, resulting in ischemic damage

Sagittal graphic depicts a large VGAM. There is an arteriovenous malformation with swirling blood within the aneurysm

. In this example, it drains into the superior sagittal sinus

Postnatal color Doppler US shows turbulent flow within the venous drainage of the VGAM. There is arterialization of the venous waveform

typical of high flow through a fistula. Up to 80% of fetal cardiac output may be diverted to the brain. This high-flow state eventually leads to cardiac decompensation.