経時的な変化で瘤形成を来した中大脳動脈遠位部の解離性脳動脈瘤の1例

Dissecting Aneurysm of the Distal Middle Cerebral Artery Formed the Out Pouch during Long-term Follow-up:A Case Report

Ⅰ．はじめに

　本邦における解離性脳動脈瘤は，椎骨動脈系に多く，内頚動脈系に少ないとされ，特に中大脳動脈遠位部では非常に稀である²⁷⁾．一方で，脳動脈解離は若年性脳卒中の10〜25%を占め²⁴⁾，虚血と出血という異なる臨床像を呈し，画像所見が経時的に変化するなど病態が複雑で，診断は必ずしも容易ではない．それゆえ虚血性脳卒中の急性期に脳動脈解離と診断されず，抗血栓薬を使用される症例が少なくないが，瘤形成を伴う脳動脈解離では抗血栓療法を控えるべきとされ¹⁷⁾，的確な診断と治療が必要となる．

　今回われわれは虚血で発症し，経過の検査で中大脳動脈遠位部に瘤形成を認め，手術により解離性脳動脈瘤の診断に至った症例を経験したので報告する．

　A 40-year-old man with a rare case of dissecting aneurysm of the distal middle cerebral artery（MCA, M2 segment）presented with ischemic stroke, manifesting as headache, nausea, and visual disorder. Computed tomography（CT）scan revealed cerebral infarction, and three-dimensional CT angiogram revealed stenotic change at the M2 segment. The patient was conservatively treated and remained neurologically stable. Ten months later, CT scan and magnetic resonance imaging（MRI）revealed outpouching of the M2 segment at the location of the initial stenosis. Angiogram revealed pearl and string sign at the M2 segment of the inferior trunk. The preoperative diagnosis was spontaneous dissecting aneurysm of the right distal MCA.

　The patient was treated with direct surgery for aneurysm resection and revascularization using the superficial temporal artery. The brain surface in contact with the dissecting aneurysm was colored xanthochromic, so minor bleeding from the dissecting aneurysm was highly suspected.

　Previously, 19 cases of dissecting aneurysm of the distal MCA have been reported. Distal dissecting aneurysms seem to rupture more frequently in the MCA than in the proximal segment. Long-term follow-up MRI and angiogram might be important, not only in the acute stage in patients with atypical caliber changes in the distal MCA. Immediate direct surgery is indicated to avoid hemorrhagic stroke if dilatation of the major trunk at the dissection is suspected.