軽微な頭部外傷を契機とする深部白質の微小梗塞で発症した中大脳動脈M2解離の1例

A Case of M2 Segment Dissection of the Middle Cerebral Artery Presenting with Deep White Matter Infarction Triggered by Minor Head Injury

Ⅰ．はじめに

　われわれは，軽微な頭部外傷後に頭痛と深部白質梗塞で発症した中大脳動脈（middle cerebral artery：MCA）M2解離の1例を経験した．後方視的には10カ月前に撮像された突発性頭痛時の画像でも軽度の紡錘状形態が認められ，今回その形状は変化していた．長期間を経て形状変化するM2解離の報告^25,26)は稀であり，文献的考察を加えて報告する．

　Herein, we report a rare case of a dissecting aneurysm of the M2 segment of the middle cerebral artery（MCA), presenting with a deep white matter infarction triggered by minor head injury. A 31-year-old woman was admitted to our hospital with headache and vomiting 3 hours after a mild head impact. A magnetic resonance angiogram obtained 10 months earlier, when the patient had complained of sudden headache, showed mild fusiform dilatation of the left M2 segment. On admission, computed tomography angiography（CTA）revealed irregular fusiform dilatation of the superior trunk of the left M2. Magnetic resonance imaging showed an intramural hematoma on the wall of the left M2 and acute infarction in the left deep white matter. Eight days after admission, CTA revealed further dilation of the aneurysm, and it was diagnosed as a dissecting aneurysm. The patient was successfully treated with proximal clipping and superficial temporal artery（STA)-MCA（M4）bypass on day 15. Bypass to a cortical M4 recipient was performed after the efferent M4 was identified using indocyanine green videoangiography. Four weeks postoperatively, the patient was discharged without any neurological deficits. The M2 dissecting aneurysm gradually regressed, and the bypass remained patent for 10 months postoperatively. To our knowledge, this is the first case of a dissecting M2 aneurysm treated by proximal clipping and STA-MCA bypass. This procedure seems a feasible option when the distal portion of the dissected MCA is difficult to expose.