Characteristics and Management of Ruptured Aneurysms Originating from the Penetrating Artery of the Distal Middle Cerebral Artery.

We report a rare case of an aneurysm originating from the penetrating artery of the distal middle cerebral artery (MCA). A 76-year-old man without a notable past history presented with sudden-onset severe headache, left hemiparesis, and a decreased level of consciousness. Computed tomography (CT) revealed subarachnoid hemorrhage (SAH) with intracerebral hemorrhage (ICH) in the right temporal lobe extending into the ventricle. Contrast-enhanced CT (CE-CT) demonstrated a focus of contrast enhancement (CE) adjacent to the hematoma in the right frontal lobe. An aneurysm fed by a penetrating artery branching off from the right distal MCA was found on angiography. The patient underwent emergency resection of the aneurysm and hematoma evacuation. Histological analysis revealed that arterial dissection may be an associated factor in the pathogenesis of this peripheral aneurysm formation. A focus of CE within or adjacent to the hematoma may be useful for diagnosing this peripheral aneurysm. ICH can result in a life-threatening situation. Therefore, microsurgery may be the first treatment choice for aneurysms in this location.