Pseudoaneurysm formation at the rupture site of a middle cerebral artery aneurysm--case report.

A 42-year-old man suffered subarachnoid hemorrhage manifesting as sudden severe headache one month before admission. On admission, his headache had subsided and he had no neurological deficits. Cerebral angiography demonstrated an aneurysm originating from the bifurcation of the right middle cerebral artery. The aneurysm was irregular, with a snowman-like shape. Neck clipping of the aneurysm was carried out through a right pterional approach. Intraoperatively, a red, pulsating sac mimicking a blood clot (the snowman's "head") was located over the yellowish, thick-walled portion of the aneurysm. Exploration around the aneurysm detached the red sac from the thick-walled portion of the aneurysm. There was a small tear in the apex of the thick-walled aneurysm sac. A Sugita clip was applied to the neck of the true aneurysm. The postoperative course was uneventful and he was discharged one month later without neurological deficits. Histological examination of the red-colored sac showed the features of pseudoaneurysm. The red sac may have been a pseudoaneurysm covering the rupture site of the true aneurysm.