We report a rare case of ruptured dissecting aneurysm of the distal middle cerebral artery. A 57-year-old male suffered from headache with a subarachnoid hemorrhage (SAH). Computed tomography showed SAH and a small intracerebral hematoma in the right frontal lobe. Three-dimensional digital subtraction angiography (DSA) using a flat panel detector (FPD) revealed irregular dilatation at the M3 portion of the right middle cerebral artery. Contrast-enhanced three-dimensional T1 weighted images showed a low-intensity mass around the abnormally dilatated right M3 branch. Surgery was performed to prevent critical rebleeding. The lesion was excised, and flow to the distal MCA branch was preserved with superficial temporal artery-middle cerebral artery anastomosis. A histological examination revealed that irregular dilatation of the right MCA was due to arterial dissection caused by disruption of the internal elastic lamina.
Three-dimensional-DSA and contrast-enhanced three-dimensional MRI were indispensable for accurate preoperative diagnosis and informed the surgeon of the exact orientation of the aneurysm.