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This is a very rare anomaly. Dilatation of entire vein is more common. Theoretically, there is a risk of rupture. But, in practice the most common complications are hydrocephalus and cardiac problems. You have not indicated whether the scan revealed hydrocephalus or not. If there is hydrocephalus, then a CSF - cerebrospinal fluid diversionary procedure may be needed. Else this condition does not require any treatment.