Complex aneurysm formation in the proximal segment of the posterior cerebral artery: a report of two cases.

Posterior cerebral artery (PCA) aneurysms are rare and often fusiform. We describe two cases of complex proximal PCA aneurysm in two women in their 60's, which probably resulted from segmental arterial degeneration. Both presented with subarachnoid hemorrhage and had common angiographic and intraoperative findings: tortuous configuration of the affected P1 segment, whitish or yellowish appearance of a portion of the lesion, lesion calcification, and multiple aneurysms in the segment. Interestingly, no significant atherosclerotic changes were noted in other cerebral arteries. The ruptured aneurysm could be successfully trapped, with superficial temporal artery (STA)-PCA bypass in one and without bypass in the other, and both patients recovered well. As complex aneurysm formation in the cases described here are probably related to proximal PCA segmental degeneration, we recommend trapping the lesion, with or without STA-PCA bypass, depending on the size and patency of the posterior communicating artery.