A case of aneurysm of the peripheral middle cerebral artery undetectable on preoperative angiogram

: The authors describe a rare case of an aneurysm of the peripheral middle cerebral artery. A 63-year-old female with a past history of hypertension suddenly fell into a comatose state, and was brought to our hospital. On admission, CT scan showed intracerebral hematoma located in the right putamen with diffuse subarachnoid hemorrhage. To exclude vascular lesions, an angiography was performed just after admission. The right carotid angiogram showed an aneurysm at the cavernous portion of the internal carotid artery (ICA), but failed to show any aneurysms in the rest of the intracranial circulation. Just after the angiography, emergent operation was performed for the main purpose of evacuation of the hematoma, and with only the secondary purpose of searching for undetectable aneurysms. The patient underwent a right frontotemporal craniotomy. After partial evacuation of the hematoma through the corticotomy of the right frontal operculum, the Sylvian fissure was opened widely. No aneurysm was observed either in the main trunk of the right ICA or the middle cerebral artery (MCA). During the final stage of evacuation of the hematoma through the corticotomy, arterial bleeding occurred. While evacuating the blood, we detected a saccular aneurysm arising from MCA branch (M2-M3 junction) and we clipped the aneurysm. We discuss peripheral MCA aneurysms with a review of the literature.