脳動脈瘤周囲浮腫の意義—Minor leakを示唆する間接所見の可能性について

Perianeurysmal Edema:An Indirect Sign of a Minor Leak from an Intracranial Aneurysm

Ⅰ．はじめに

　脳動脈瘤周囲浮腫（perianeurysmal edema：PAE）は，主に部分血栓化巨大動脈瘤³⁾やコイル塞栓術後動脈瘤⁵⁾などで指摘されており，通常の脳動脈瘤に関する報告は少ない^4,6)．今回われわれは，頭痛精査時のMRI/MRAで長径約10mmのダンベル型中大脳動脈瘤を指摘され，脳実質に埋没したbleb周囲にPAEと思われるT2延長域を認めた症例を経験した．術中所見では，minor leakを来した亜急性〜慢性期の破裂動脈瘤であると考えられた．PAEが一般的な脳動脈瘤で認められることは稀であり，その意義について，文献的考察を加えて報告する．

　We report a rare case of perianeurysmal edema（PAE）around the dome of a usual intracranial aneurysm. A 79-year-old woman who presented with a dull headache that had become stronger from a month before was referred to our hospital for further examination of an aneurysm. MR angiogram had detected the aneurysm, having a dumbbell shape and arising from the M2 bifurcation of the right middle cerebral artery. Initial fluid attenuated inversion recovery and T2 weighed images revealed a slightly high intensity area in the brain around the dome of the aneurysm buried in the right temporal lobe, suggesting the presence of PAE possibly due to a preceding minor leak or partial thrombosis or impending rupture of the aneurysm. A CT angiogram revealed bleb formation of the aneurysm（size:10×6 to 4mm）without definite intraluminal thrombosis.

　The patient and her family consented to emergency craniotomy. During the microsurgical approach, thickening of the arachnoid membrane on the right sylvian fissure was observed. The subarachnoid space between the right frontal and temporal lobes was turbid/adhesive, and deposition of hemosiderin was observed around the aneurysm, indicating a preceding minor bleeding. The aneurysm was successfully clipped, and the postoperative course was uneventful.

　The present case showed that PAE could be observed even in a usual aneurysm. This finding might be an indirect sign of a preceding minor leak from the aneurysm, particularly when the dome is buried in brain parenchyma or is in close contact with the surrounding brain surface.