中大脳動脈閉塞に伴うleptomeningeal anastomosis上に発生した破裂脳動脈瘤の1例

A Case of Repeated Intracerebral Hemorrhage due to a Ruptured Aneurysm of Collateral Circulation from the Posterior Cerebral Artery to the Middle Cerebral Artery

Ⅰ．はじめに

　主幹動脈閉塞に伴う脳動脈瘤はしばしば報告され，その発生機序の1つとしてhemodynamic stressが考えられている．これらの動脈瘤はWillis動脈輪に発生する場合が多いが，皮質枝に生じる症例も稀ながら報告されている．また，脳動脈瘤破裂は通常くも膜下出血（SAH）で発症するが，動脈瘤の位置や過去の出血歴などにより，脳内血腫のみで発症する場合もあり，診断を進める上で注意が必要である．今回われわれは，中大脳動脈（MCA）の閉塞に伴い，同側後大脳動脈（PCA）から側副血行路として発達したleptomeningeal anastomosis上に生じた脳動脈瘤の破裂により脳内血腫を生じた症例を経験したので報告する．

　We present a case of ruptured distal middle cerebral artery aneurysm associated with occlusion of the anterior trunk of the ipsilateral middle cerebral artery.

　An 83-year-old man had right homonymous hemianopsia and right mild hemiparesis. CT scan revealed hematoma and a perifocal low density area at the left occipital subcortex without subarchnoid hemorrhage (SAH). MRI showed repeated bleeding at the same location as the CT scan. Moreover, cerebral angiograms disclosed an aneurysm on the leptomeningeal anastomosis from the left posterior cerebral artery to the middle cerebral artery. The anterior trunk of the left middle cerebral artery was occluded at the origin. The aneurysm was not situated at the bifurcation and was trapped without new neurological complications.

　This case suggested that hemodynamic stress due to occlusion of the main artery contributed to the development of an aneurysm at the collateral artery. Even if intraparenchymal hematoma presents without SAH, and even if it is located at a rare site for aneurysms, we should inspect the source of bleeding considering factors preventing SAH arising from aneurysms.