側副血行路起始部(A1)と前交通動脈に未破裂脳動脈瘤を伴う無症候性aplastic or twig-like middle cerebral artery—動脈硬化性頭蓋内血管多発狭窄を合併した1例

Asymptomatic Aplastic or Twig-Like Middle Cerebral Artery Associated with Unruptured Cerebral Aneurysms at the Origin (A1) of a Collateral Artery and the Anterior Communicating Artery: A Case Report with Multiple Intracranial Atherosclerotic Stenoses

無症候性Ap/T-MCAの側副血行路起始部（A1）に発生した未破裂A1動脈瘤を経験した。当初動脈硬化性病変と捉えていたが，詳細な画像検査と術中所見からAp/T-MCAと診断した。動脈瘤破裂による出血例が多い破格であり，二次的に動脈硬化が合併している可能性にも留意すべきである。小型でも破裂しやすく，未破裂動脈瘤には積極的なバイパス併用根治術もオプションの1つとなり得るが，さらなる知見の集積が必要である。

Abstract

We report a rare case of asymptomatic aplastic or twig-like middle cerebral artery (Ap/T-MCA) with small unruptured aneurysms at the origin (A1) of the anomalous collateral artery containing plexiform (twig-like) networks and in the anterior communicating artery. In Ap/T-MCA, other cerebrovascular systems are usually considered to exhibit normal findings not associated with atherosclerosis. At first admission, atherosclerotic M1 occlusion was suspected because of the patient's risk factors and multiple stenoses in major intracranial arteries. Cerebral blood flow (CBF) studies revealed reduction of resting CBF and vascular reserve in the ipsilateral MCA territory. After 5 years, a diagnosis of Ap/T-MCA was reached based on detailed image examination and intraoperative findings during aneurysm clipping in combination with extracranial-intracranial (EC-IC) bypass. It should be noted that atherosclerosis can coexist with Ap/T-MCA, which is considered a congenital anomaly in which bleeding often occurs due to a ruptured aneurysm within the fragile collateral vessels. In previous reports, A1 aneurysms at the origins of the collateral arteries ruptured even when they were small. Aggressive radical surgery using EC-IC bypass can be considered for the treatment of unruptured aneurysms associated with Ap/T-MCA, but further research is needed.

(Received September 14, 2020; Accepted November 4, 2020; Published 1 April, 2021)