Specific Imaging Findings Prenatal ultrasound in vein of Galen aneurysmal malformation (VGAM) shows a midline cystic structure in the region of the quadrigeminal plate with intraluminal flow. Prenatal MRI shows the dilated pouch and draining sinus, hypointense on all imaging sequences due to flow phenomena. On postnatal MRI a dilated rounded to ovoid or tubular venous ampulla in the region of the quadrigeminal cistern and velum interpositum is again hypointense on all sequences, of variable, usually quite large dimensions. The arterial feeders are seen as multiple small flow-voids surrounding the ampulla; on MRA they appear to converge to the VGAM, whereas distal flow in the main cerebral arteries is not well seen. The draining vein is a persistent falcine sinus (instead of the nondeveloped straight sinus). Relative stenosis of the outflowing vein is often seen at the tentorial hiatus just below the callosal splenium. Patency of the draining vein and sinuses, especially at the sigmoid–jugular junction, must be assessed. The brain parenchyma should be carefully scrutinized for signs of injury including encephalomalacia, atrophy, subcortical calcifications, and ventriculomegaly. Herniation of cerebellar tonsils may be a consequence of venous hypertension. Catheter angiography elucidates the anatomy and pathophysiology of VGAM, but should be reserved for endovascular treatment. Pertinent Clinical Information Neonates with VGAM present with congestive cardiac failure – tachycardia, respiratory distress and cyanosis. During early infancy, macrocrania may appear as a consequence of maturational delay of the dural sinuses and granulations, or due to cerebral aqueduct compression by the dilated pouch, leading to hydrocephalus and intracranial hypertension. Older children usually present with chronic headache and hydrocephalus or seizures. Treatment is by transarterial embolization, and the optimal therapeutic window at 4–5 months of age has shown the best efficacy in controlling the malformation and allowing the brain to normally mature and develop. Earlier treatment carries a higher risk of failure and comorbidity; it may be contemplated in rapidly progressive cases with unresponsive heart failure. Severe diffuse brain injury is a contraindication for endovascular treatment. Spontaneous VGAM thrombosis has been described in rare cases.
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