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Acute obstructive hydrocephalus due to an unruptured basilar bifurcation aneurysm associated with bilateral internal carotid occlusion--a case report.

A patient with a higherly positioned and large basilar bifurcation aneurysm associated with bilateral internal carotid occlusion was described. A 63 year-old man was admitted to Yokokura Hospital with disturbed consciousness and mild left hemiparesis. On admission, an initial plain CT-scan showed an acute obstructive hydrocephalus with periventricular lucency caused by an abnormal lesion in the anterior part of the third ventricle. An emergency ventriculo-peritoneal shunt was inserted. The postoperative course was uneventful. The patient regained his consciousness with normal motor function by the following day. Postoperative cerebral angiography disclosed a large basilar bifurcation aneurysm at a higher position, 19 mm from the dorsum sellae. Bilateral internal carotid occlusion had occurred, but rich collateral blood supply from the vertebro-basilar artery via the bilaterally enlarged posterior communicating arteries to the anterior circulation was observed. This rich collateral blood supply to the vertebrobasilar artery might be responsible for the development of the aneurysmal formation due to the increased hemodynamic stress.