Obstructive hydrocephalus at the anterior third ventricle caused by dilated veins from an arteriovenous malformation.

A dilated thalamostriate--internal cerebral vein complex, draining a right frontoparietal arteriovenous malformation, caused a physical block at the foremen of Monroe and was the cause of obstructive hydrocephalus. It represents a new mechanism of obstructive hydrocephalus formation in patients with arteriovenous malformations, which has not been previously reported. There was no history of subarachnoid hemorrhage. Embolization, followed by resection, was successfully carried out. This case was reported because of its unusual nature and to discuss potential problems to be avoided in dealing with intraventricular arteriovenous malformations.