後下小脳動脈anterior medullary segmentに発生した破裂脳動脈瘤の2手術例―穿通枝温存と後下小脳動脈の虚血について

Ruptured Aneurysm Arising from the Anterior Medullary Segment of the Posterior Inferior Cerebellar Artery : Report of Two Cases

　Ⅰ．はじめに

　後下小脳動脈（posterior inferior cerebellar artery ; PICA）に生じる脳動脈瘤の中で，近位部のanterior medullary segment（AMS）に発生する脳動脈瘤は比較的稀である．Choroidal pointより近位側には，下位脳幹への穿通枝が存在することが知られており²³⁾，治療方針については見解が一致していない^{1,6,11,17,32)}．今回われわれは，PICA近位側に発生した非解離性の破裂脳動脈瘤2例を経験したので，治療戦略について若干の文献的考察を加え報告する．

　In the distal posterior inferior cerebellar artery (PICA),saccular aneurysms originating at the first proximal segment,anterior medullary segment (AMS),are unusual but important due to the presence of critical perforators that branch off the PICA and supply the lower brainstem. Because the anatomy of the PICA varies,no standard treatment strategy has been agreed upon to date. We successfully treated 2 patients with open surgery. One was a 53-year-old man who presented with Hunt-Hess grade 2 subarachnoid hemorrhage (SAH). Cerebral angiography revealed an irregular fusiform AMS aneurysm extending to the lateral medullary segment. Intraoperative inspection showed some perforators to the brain stem branching from just proximal and distal to the aneurysm. The patient underwent aneurysmal trapping and occipital artery-PICA anastomosis to preserve perforators flow,and was discharged without any neurological deficits. Another patient,a 74-year-old woman,was transferred to our institute because she suddenly became comatose. She was found to have a ruptured saccular AMS aneurysm. On the 15th day after the event,she underwent successful aneurysmal clipping preserving perforators by surgical inspection. As both patients manifested intra-aneurysmal thrombosis,we suggest that patients presenting with AMS aneurysms that display unusual features require careful management and judicious choice of treatment. Based on our experience we suggest that direct surgery,which facilitates the identification of perforators and allows for revascularization,is the appropriate treatment choice in patients who present with this entity.