破裂PICA交通動脈瘤の1例

Ruptured Posterior Inferior Cerebellar Artery Communicating Artery Aneurysm:A Case Report

Ⅰ．はじめに

　後下小脳動脈（posterior inferior cerebellar artery：PICA）の解剖はバリエーションが多い．両側のPICAを交通する側副血管は，PICA communicating artery（PICA交通動脈）として知られている．この血管はPICAのchoroidal arch近傍以遠より生じてarterial bridgeを形成し，一側のPICAからvermisを越えて対側PICAの支配領域へ灌流している¹⁾．

　1991年，Hlavinら⁵⁾はこの血管に生じた動脈瘤（artery aneurysm：AN）をPICA communicating artery aneurysm（PICA交通動脈瘤）として初めて報告した．PICA末梢部の動脈瘤は比較的少なく，さらにPICA本幹ではなくこの側副血管に生じた動脈瘤は極めて稀で，いまだ十分に認知されていない．今回，われわれは破裂PICA交通動脈瘤の1例を経験したので，文献的考察を加えて報告する．

　The posterior inferior cerebellar artery（PICA）communicating artery is a fine tortuous artery that interconnects the bilateral vermian branches of the distal PICAs. Aneurysms of this anastomotic vessel have been reported in only seven cases（including ours）in the available literature. The PICA communicating artery supplied collateral blood flow to the contralateral vermian territory in all seven cases. A 51-year-old man presented with a rare PICA communicating artery aneurysm（which manifested as a hematoma in the fourth ventricle）and mild subarachnoid hemorrhage at the cerebellomedullary fissure. Angiography revealed a hypoplastic right PICA and a PICA communicating artery from the left PICA that supplied the right vermian territory；the ruptured aneurysm originated from this vessel. Aneurysm trapping is associated with the risk of cerebral infarction of the right vermian territory. We concluded that the distal part of the telovelotonsillar segment could be sacrificed because the right anterior inferior cerebellar artery and the superior cerebellar artery would supply collateral blood flow；therefore, we attempted trapping in this case. A bilateral midline suboccipital approach was used, and we detected a reddish fusiform aneurysm at the top of a hairpin curve of the PICA communicating artery in the uvula of the cerebellar vermis. The aneurysm was trapped and removed without complications. Histopathological evaluation confirmed findings of a true aneurysm. Congenital vulnerability of the arterial wall and hemodynamic stress are considered contributors to PICA communicating artery aneurysms. Preservation of the affected vessel is difficult in patients in whom aneurysmal clipping is challenging. Other vessels tend to establish collateral blood flow to the contralateral vermian territory in such cases. Trapping is a simple and effective therapeutic strategy for these aneurysms.