Accessory anterior cerebral arteryに発生した末梢性前大脳動脈瘤の2症例

Two Cases of Distal Anterior Cerebral Artery Aneurysm Associated with Accessory Anterior Cerebral Artery

Ⅰ．は じ め に

　Accessory anterior cerebral artery（以下，accessory ACA）は前交通動脈から直接分枝し，本来の前大脳動脈（ACA）の支配領域を支配しているもので，通常2本の前大脳動脈（A2）に加え前交通動脈からあたかも3本目の枝があるようにみえるためtriple ACA，third ACAなどとも呼ばれる前大脳動脈の血管奇形の1つである．

　一般に末梢性前大脳動脈瘤はほとんどが脳梁膝部に発生し，それ以外の部位に発生した動脈瘤は非常に珍しいとされる．今回われわれは，前大脳動脈の奇形であるaccessory ACA末梢部に発生した未破裂脳動脈瘤の2例を経験した．Accessory ACA末梢に発生した脳動脈瘤は稀で報告は非常に少なく，今回経験した2症例について手術所見を含め文献的に考察し報告する．

An accessory anterior cerebral artery (accessory ACA) is a rare anomalous vessel arising from the anterior communicating artery as a median artery of triplicated ACA. It is considered a large median artery of the corpus callosum and distributes to one or both hemispheres. The cases of an accessory ACA aneurysm are extremely rare; however,we experienced two cases of unruptured aneurysm growing at the distal portion of an accessory ACA. Two females,aged 66 and 67 years,respectively,separately consulted our hospital as a result of chronic headaches. Brain MR angiography and following DSA in the first patient demonstrated a triplicated ACA and an aneurysm located just above the corpus callosum growing from the distal portion of the accessory ACA. MRI and MR angiography in the second patient depicted a triplicated ACA and an aneurysm from the accessory ACA as with the first case. Neck clipping of the aneurysm was performed using an interhemispheric approach in both cases. These aneurysms appeared to present the same intraoperative findings as other unruptured aneurysms growing at the usual positions.