破裂右中大脳動脈遠位部（M2）解離性動脈瘤の1例—症例報告および文献的考察

Ruptured Dissecting Aneurysm of M2 Portion of the Middle Cerebral Artery:A Case Report

Ⅰ．はじめに

　本邦において頭蓋内の解離性動脈瘤は，非出血例，出血例ともに椎骨脳底動脈系に発生する頻度が高く（87.4%），内頚動脈系は少ない（12.6%）³⁾．発症様式は，脳卒中データバンク2015によると，椎骨脳底動脈系，内頚動脈系で非出血例が多く，それぞれ71.5%，72.4%であった⁴⁾．頭蓋内に発生する解離性末梢性動脈瘤は，通常，頭部外傷，血管炎，感染性心内膜炎に関係した細菌感染などにより発生することが多い．今回われわれは，非外傷性で，特に誘因なく発症した破裂中大脳動脈遠位部解離性動脈瘤（M2 inferior trunk）の症例を経験した．症例を提示し，中大脳動脈遠位部解離性動脈瘤の臨床的特徴と治療戦略について考察する．

　A 71-year-old woman presented with a sudden onset of headache and vomiting. Computed tomography（CT）showed diffuse subarachnoid hemorrhage（SAH）that was more severe on the right side. Three-dimensional CT angiography and right carotid angiography（CAG）demonstrated 2-mm microaneurysms at the middle cerebral artery（MCA）bifurcation and anterior communicating artery, with slight narrowing and dilatation of the M2 inferior trunk. Each microaneurysm was smooth, making it difficult to identify the bleeding source. Thus, surgery was postponed at the acute stage, and further investigation was planned. Repeated CAG was diagnostically unsuccessful, finding no source of the bleeding. On day 45 after the onset, exploratory craniotomy was performed to confirm the cause of the SAH. During the operation, both microaneurysms were found to be unruptured. However, the distal portion of the M2 inferior trunk was dark purplish and red and enlarged in a fusiform shape, suggesting a dissecting aneurysm. Residue of the SAH observed near the enlarged vessel identified it as the bleeding source. The enlarged vessel was wrapped with Bemsheets, and the Bemsheets was clipped to secure it. A dissecting aneurysm of the distal MCA is rare, as is the onset of bleeding. Based on a review of the literature related to dissecting aneurysms of the distal MCA, we recommend exploratory craniotomy if CT demonstrates laterality of the sylvian fissure on the SAH and CAG reveals stenosis or occlusion of the distal MCA in cases of SAH for which no bleeding source is detected.