Giant aneurysm of anterior communicating artery simulating 3rd ventricular tumor.

This is a case report of an anterior communicating artery aneurysm simulating a 3rd ventricular tumor with obstructive hydrocephalus demonstrated on CT scan. Angiography showed the "tumor" to be an aneurysm. We believe that giant aneurysms of the anterior communicating artery should be included in the differential diagnosis of suspected 3rd ventricular tumors along with suprasellar masses as seen on CT scans.