顕微鏡的多発血管炎に合併した脳動脈瘤破裂の1例

A Case of a Ruptured Cerebral Aneurysm Associated with Microscopic Polyangiitis

Ⅰ．はじめに

　抗好中球細胞質抗体（anti-neutrophil cytoplasmic antibody：ANCA）関連血管炎は希少性で原因不明の難治性疾患であり，この中には顕微鏡的多発血管炎（microscopic polyangiitis：MPA），Wegener肉芽腫症（Wegener's granulomatosis：WG），好酸球性多発血管炎性肉芽腫症（eosinophilic granulomatosis with polyangiitis［EGPA］．従来，アレルギー性肉芽腫性血管炎/Churg-Strauss症候群［AGA/CSS］と呼ばれていた），腎限局型血管炎（renal-limited vasculitis：RLV）の4疾患が含まれる²⁾．これらの脳血管障害合併例としては，EGPAに動脈瘤¹⁰⁾や脳梗塞³⁾が合併した報告や，WGにくも膜下出血が合併した報告¹⁾が散見される．しかし，MPAに動脈瘤が合併して破裂した報告は極端に少なく，渉猟し得た限りではKimuraらの報告のみであった⁴⁾．

　今回MPAに合併した末梢性右中大脳動脈瘤破裂患者に対して開頭クリッピング術を施行した際，動脈瘤頚部へのクリップの機械的刺激により，動脈瘤が母血管から容易に離脱した．血管炎由来の脳動脈瘤であり，血管壁が脆弱であったためと考えられる¹⁰⁾．稀な病態であり，かつ，教訓的な症例であったため報告する．

　CASE:A 71-year-old woman was receiving dialysis for microscopic polyangiitis（MPA). She was transported to the emergency room after developing a headache and losing consciousness. She was in a coma and had dense left paralysis. Head computed tomography（CT）showed a subarachnoid hemorrhage. Head three-dimensional CT angiography showed an aneurysm proximal to the right M2（inferior trunk), which was considered as the source of bleeding. We performed an emergency aneurysm clipping surgery. However, we placed a permanent clip on the arterial wall defect when the clip detached from the parent artery. Pathological examination of the aneurysm revealed that the layered structure of the artery was damaged because of fibrin degeneration, suggesting that the aneurysm was caused by vasculitis. Coma persisted after surgery, and the patient was transferred to another hospital.

　DISCUSSION:We found only one report demonstrating an association between a cerebral aneurysm and MPA. Aneurysms resulting from vasculitis are common at the periphery, rather than at vessel bifurcations. Cyclic inflammatory activity causes progressive destruction of the blood vessel wall, further expanding the lumen and forming an aneurysm. Therefore, such aneurysms are more fragile than true aneurysms, and are more likely to be damaged or detached during surgery, as in the present case. Trapping of the parent artery should be considered when the aneurysm is damaged or detached. Accordingly, preoperative planning could anticipate the need for superficial temporal artery to middle cerebral artery bypass.