STA-MCA吻合術後消失したと思われる，特発性中大脳動脈閉塞症に合併した脳動脈瘤の1症例

A case of spontaneous middle cerebral artery occlusion associated with a cerebral aneurysm angiographically disappearing after STA-MCA anastomosis

I．はじめに

　モヤモヤ病の側副血管には血流負荷によると考えられる動脈瘤が生ずることは広く知られている^10）．またモヤモヤ病に合併した末梢性動脈瘤は親血管への血流負荷の変化でしばしば自然消失する^8）．

　今回われわれは脳虚血発作で発症し，経過観察中に脳底部異常血管網の小動脈瘤が短期間で増大を来たした特発性中大脳動脈閉塞症の症例を経験した．さらに浅側頭動脈—中大脳動脈吻合術後短期間で動脈瘤の消失をみた．動脈瘤の消失は血管吻合術後に親血管である脳底部異常血管網への血流負荷が減少したためと考えられたので，特発性中大脳動脈閉塞症に関する文献的考察を加え報告する．

We report a case of a rapidly growing cerebral aneu-rysm in the basal abnormal vascular network associated with spontaneous middle cerebral artery (MCA) occlu-sion. The aneurysm disappeared spontaneously shortly after performing STA-MCA anastomosis.

A 54-year-old female was admitted to our hospital because of repeated attacks of right hemisensory dis-turbance and dysarthria. CT scan and MRI images showed the infarcted focus in the left parieto-occipital lobe. Bilateral MCAs were undetectable on MRI im-ages. Cerebral angiography revealed that the bilateral MCAs were occluded in their proximal origin with bas-al abnormal vascular networks. The distal MCA bran-ches were perf used via the vascular networks. A small aneurysm was detected in the distal portion of the left Heubner's artery. There were no abnormalities in the bilateral internal carotid arteries, the anterior cerebral arteries, and the basilar artery. The follow-up angiogra-phy performed 29 days after admission revealed a growing aneurysm with a diameter of 3mm in the distal portion of the left Heubner's artery that formed abnor-mal basal vascular network. CT scan also showed an enhanced lesion consistent with the aneurysm observed in the angiography.

An STA-MCA anastomosis was performed for im-provement of cerebral misery perfusion. Single photon emission tomography (SPECT) performed 9 days after the bypass operation revealed improvement of cerebral blood flow in the left parieto-occipital lobe, and her TIA attacks disappeared. The aneurysm was undetect-ed in the cerebral angiography performed 24 days after the bypass operation.

Spontaneous MCA occlusion is a rare condition of chronic cerebrovascular occlusive diseases. Diagnostic criteria of the disease includes the MCA occlusions or stenosis with basal abnormal vascular networks. Usual-ly the phenomenon is seen unilaterally, which differs from moyamoya disease. Diagnosis must exclude dis-eases caused by the etiologies such as those of arter-iosclerotic origin. There have been 24 reported cases of spontaneous MCA occlusion including our case. Among them, 9 cases presented cerebral aneurysm located in abnormal vascular networks, and all the reported cases presented cerebral hemorrhage at their onset.

The abnormal basal vascular network may be de-veloped as collateral vessels to supply blood to the ischemic regions in this disease. An increased hemody-namic stress in the abnormal basal vascular network may produce a true aneurysm in the distal portion of the perforating arteries. STA-MCA anastomosis re-duced the TIA attacks, but also decreased the hemo-dynamic stress on the abnormal basal vascular network and resulted in reduction in size or thrombosis of the aneurysm. STA-MCA anastomosis can be considered effective to treat cerebral aneurysms located in vessels with increased hemodynamic stress.