[A case of unruptured fusiform aneurysm in a middle cerebral artery branch].

We report a case of a 55-year-old female presenting with headache. Neuroradiological investigations revealed a fusiform aneurysm at the M3 part of the right middle cerebral artery. The aneurysm rapidly developed in the course of one year. She underwent a craniotomy for superficial temporal artery middle cerebral artery bypass (STA-MCA bypass) and resection of the aneurysm. Pathological examination suggested that atherosclerosis was a predisposing factor for aneurysm formation. Although she had developed transient dysarthria and left-hand clumsiness after the operation, she was able to be discharged after 26 days with no neurological deficits. On reviewing the literature, fusiform aneurysms seem to be an important cause of subarachnoid hemorrhage and cerebral infarction of unverified origin. Etiology and treatment of spontaneous fusiform aneurysms in a branch of the middle cerebral artery are also discussed.