You are shown two raw data images from an MRA/MRV and a sagittal thin-section T2 image. What is the diagnosis (arrows), what is the most likely blood supply, and which vein is persistently dilated as a result of this entity?
The findings are consistent with a vein of Galen (arrow) malformation (VOGM). The feeders are usually via posterior choroidal feeders and thalamoperforates with rapid drainage into a dilated median prosencephalic vein which normally involutes. Often, the posterior communicating artery and posterior cerebral arteries are dilated (not shown). Vein of Galen arteriovenous malformations of the medial prosencephalic system account for 30 percent of cerebral malformations in the pediatric age group. It is the most common intrauterine diagnosed intracranial vascular malformation.
Neonatal presentation is usually the choroidal type with high output cardiac failure and an intracranial bruit. The infant type is more mural and may present with hydrocephalus due to venous hypertension or aqueductal stenosis. Delayed presentations in childhood include developmental delay and hydrocephalus, usually in the mural type. The cerebral arteriovenous fistula of the median prosencephalic vein (MPV) occurs at 6-11 weeks gestation. The MPV fails to regress and becomes aneurysmal and drains via the straight sinus or persistent falcine sinus and the vein of Galen does not actually form. The straight sinus is present only 50 percent of the time. Note that the vein of Galen may dilate secondary to high-flow parenchymal AVM (Yasargil 4).
Vein of Galen aneurysms are often classified via the Yasargil system:
- Type 1: small pure cisternal fistula between the vein of Galen and either pericallosal arteries (anterior or posterior) or posterior cerebral artery.
- Type 2: Multiple fistulous communications between the vein of Galen and the thalamoperforating vessels.
- Type 3: High-flow mixed type 1 and type 2. Flow voids are apparent.
- Type 4: Parenchymal arteriovenous malformation (AVM) with drainage into the vein of Galen.
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