Middle Cerebral Artery Aneurysm Associated with Moyamoya Disease

BACKGROUND: We report a rare case of unruptured middle cerebral artery aneurysm associated with moyamoya disease. CASE DESCRIPTION: A 48-year-old woman with an 8-year history of moyamoya disease developed a de novo aneurysm at the bifurcation of the right middle cerebral artery. The aneurysm showed rapid enlargement in size in 1 year and surgical treatment was performed. Preoperative images could not clearly define the anatomical relationship between the aneurysm and the surrounding vessels. Intraoperative findings indicated that segmental occlusion of normal arteries that was not visualized made it difficult to define the vascular anatomy. In addition, those occlusions accompanied by improved M1 flow after administration of cilostazol was speculated to have increased hemodynamic stress, leading to the relatively rapid progress of the aneurysm. CONCLUSIONS: Understanding the complexity of such process may be valuable in proper decision-making in the management of moyamoya disease patients.