Internal carotid-posterior communicating artery aneurysm associated with unusually short posterior communicating artery

We report two cases of a ruptured internal carotid-posterior communicating artery aneurysm in which the ipsilateral posterior communicating artery is short and the P1 and P2 segments of the posterior cerebral artery are long. Unique angiographic and operative findings are described. Vertebral angiog raphy with carotid compression is recommended to diagnose this rare variati on. Recognition of this variation is important to avoid an inadvertent occl usion of arteries behind the aneurysm at the time of clipping. (C) 1999 Har court Publishers Ltd.