Pseudoaneurysm at M3 of the middle cerebral artery: Morphological changes on serial radiological examinations.

A 20-year-old man presented with consciousness disturbance and hemiparesis, and computed tomography demonstrated subarachnoid and intracerebral hemorrhage. Angiography on admission demonstrated a slight irregularity of the middle cerebral artery (MCA) branch. Angiography on the 12th day showed a suspicious lesion at M3 of the left MCA. Angiography performed 24 days after the onset disclosed an aneurysm at M3. The aneurysm was trapped and resected after superficial temporal artery-MCA bypass. Pathological examinations revealed that this distal aneurysm was a pseudoaneurysm without vascular components in its dome. Although a lesion that may cause subarachnoid or intracerebral hemorrhage was not detected on the initial angiography, repeated examinations revealed the atypical vascular lesion in distal MCA.