[A Case of Aplastic or Twig-like Middle Cerebral Artery with a Ruptured Aneurysm at an Anomalous Collateral Artery].

A 69-year-old man presented with sudden loss of consciousness and was admitted to our hospital. Computed tomography revealed diffuse subarachnoid hemorrhage. Digital subtraction angiography revealed occlusion of the left M1 segment, collateral arteries from the left A1 to the left M2 via twig-like networks, and a 6-mm aneurysm in the collateral arteries. Clipping surgery was performed on the 3rd hospital day. Vascular abnormalities of the middle cerebral artery with twig-like networks have been reported with an incidence of 0.11-0.17%. In addition, aneurysms are reported as complications in 40% of cases, suggesting hemodynamic stress and structural vulnerability. (Received January 16, 2018; Accepted June 21, 2018; Published September 1, 2018).