Abstract
A rare case of Moyamoya disease associated with an accessory middle cerebral artery (accessory MCA), in which a saccular aneurysm was found at its origin is reported. Neck clipping of the aneurysm was performed along with the superficial temporal artery–MCA bypass. Intraoperative observation revealed that the terminal portion of the ICA, M1 portion and the superior trunk of the MCA, and the A1 portion of the contralateral anterior cerebral artery were affected by Moyamoya disease, while no definite change was found in the accessory MCA. The accessory MCA itself suffers from hemodynamic stress at its origin because of its recurrent configuration. In the present case, as the arteries around the circle of Willis were affected by Moyamoya disease after birth, the accessory MCA worked as an important collateral pathway, which consequently caused additional hemodynamic stress, resulting in an aneurysm formation at its origin.
