[Peripheral branch (P4 segment) aneurysm of the posterior cerebral artery: a case report].

Four to fifteen percent of all intracranial aneurysms reported are peripheral aneurysms of the posterior fossa. Peripheral branch aneurysm of the posterior cerebral artery has only rarely been described. A 69-year-old woman had sudden onset of severe headache and vomiting and was transferred to our hospital. On admission the patient showed mild mental impairment. She had signs of meningeal irritation and right homonymous hemianopsia. CT scan showed intracerebral hematoma in the left occipital lobe, large hematoma in the left lateral ventricle and subdural hematoma in the interhemispheric region. The left carotid angiogram showed an aneurysm on the parieto-occipital artery of the left posterior cerebral artery. On the 13th day from onset left occipital craniotomy was performed. When the dura was opened, subdural hematoma was seen and removed by suction. A saccular aneurysm measuring 4 X 8 mm in diameter was seen on the parieto-occipital artery. Neck clipping for the aneurysm was successfully performed and the aneurysm disappeared completely in the postoperative angiographical study. Postoperative course was uneventful and the patient was discharged.