[Dissecting Aneurysm of the Distal Middle Cerebral Artery Formed the Out Pouch during Long-term Follow-up:A Case Report].

A 40-year-old man with a rare case of dissecting aneurysm of the distal middle cerebral artery(MCA, M2 segment)presented with ischemic stroke, manifesting as headache, nausea, and visual disorder. Computed tomography(CT)scan revealed cerebral infarction, and three-dimensional CT angiogram revealed stenotic change at the M2 segment. The patient was conservatively treated and remained neurologically stable. Ten months later, CT scan and magnetic resonance imaging(MRI)revealed outpouching of the M2 segment at the location of the initial stenosis. Angiogram revealed pearl and string sign at the M2 segment of the inferior trunk. The preoperative diagnosis was spontaneous dissecting aneurysm of the right distal MCA. The patient was treated with direct surgery for aneurysm resection and revascularization using the superficial temporal artery. The brain surface in contact with the dissecting aneurysm was colored xanthochromic, so minor bleeding from the dissecting aneurysm was highly suspected. Previously, 19 cases of dissecting aneurysm of the distal MCA have been reported. Distal dissecting aneurysms seem to rupture more frequently in the MCA than in the proximal segment. Long-term follow-up MRI and angiogram might be important, not only in the acute stage in patients with atypical caliber changes in the distal MCA. Immediate direct surgery is indicated to avoid hemorrhagic stroke if dilatation of the major trunk at the dissection is suspected.