部分血栓化にて発症した未破裂上小脳動脈末梢部動脈瘤の1例

Spontaneous Partial Thrombosis of an Unruptured Peripheral, Superior Cerebellar Artery Aneurysm : A Case Report

I．はじめに

　上小脳動脈末梢部動脈瘤は稀な脳動脈瘤であり，大部分はくも膜下出血にて発症し，脳神経麻痺を伴うことが多いとされる．今回われわれは上小脳動脈末梢部動脈瘤が破裂ではなく，部分血栓化により発症した症例を経験した．脳動脈瘤の自然血栓化は稀な病態であるが，上小脳動脈末梢部という稀な部位の未破裂動脈瘤が，いかなる機序で部分血栓化を来したのか興味が持たれた．同部位の血栓化動脈瘤の報告例はほとんどなく，今回われわれは瘤内血栓化の過程を初期の段階から画像的に捕らえることができたため，上小脳動脈末梢部における未破裂動脈瘤の自然血栓化の発生機序を画像所見を中心に検討し，若干の文献的考察を加え報告する．

A 52-year-old female suddenly developed headache and dizziness. On admission she complained of gaitdisturbance with dizziness but cranial nerve palsy could not be detected. CT scan revealed a mild high den-sity lesion in the right ambient cistern and the density of the lesion had become much higher 5 days afteradmission. MRI revealed a homogeneous iso-intense lesion on T1WI, T2WI 2 days after admission and thelesion had changed to homogeneous high. The lesion was suspected to be a fresh thrombus. Right verteb-ral angiography showed a part of the aneurysm arising from the ambient segment of the right superiorcerebellar artery and we diagnosed the lesion as a partially thrombosed superior cerebellar arteryaneurysm. About forty cases of peripheral superior cerebellar artery aneurysm have been described in theliterature, but cases of spontaneous thrombosis of the aneurysms have been very rare. Spontanous throm-bosis of aneurysms was usually thought to occur in large aneurysms, but the aneurysm in our case was notlarge. We suspected that in our case spontanous thrombosis may have been caused by occlusion of the pa-rent artery of the aneurysm.