大型脳動脈瘤におけるMRI瘤壁評価の有用性―3症例報告

Preoperative Evaluation of the Aneurismal Wall by Using High-resolution MRI: Report of 3 Cases

Ⅰ．はじめに

　比較的大型の動脈瘤の開頭クリッピング術の問題点の1つに血栓化の有無と瘤壁の厚さがある．血栓化を伴うものや瘤壁が厚いものは，単純にクリッピングできないものも多く，バイパス術＋親動脈閉塞や瘤内血栓除去など別のstrategyを必要とすることがある^5,8)．血栓化の状態や瘤壁の評価を術前に行うことができればstrategyを立てる上で有用であるが，実際には評価は難しくクリッピングできるかどうかの判断は術中所見に委ねられることが多いと思われる．近年，black-blood imagingなど動脈壁のimagingが進歩しつつあり^1-4,9-11)，われわれも3 tesla-magnetic resonance imaging（MRI）装置による高解像度T2強調画像を用いて頭蓋内動脈のplaque評価などを行ってきた⁶⁾．今回本法を大型脳動脈瘤に応用し，術前の血栓化や壁厚の評価が有用であった3症例を経験したので報告する．

　Surgical treatment of large cerebral aneurysms may depend on preoperative information regarding the wall thickness and the intraaneurysmal thrombosis. When the neck of an aneurysm is thick due to atherosclerosis or there is a marked thrombosis inside the aneurysm, clipping may not be possible. Here we report three cases with large internal carotid artery aneurysms that were evaluated for the thickness of the aneurysm wall and the presence of thrombosis by 3 tesla magnetic resonance (MR) imaging. A high-resolution T2-weighted imaging (HRT2WI) modified for 3 tesla was used. In two cases, the images showed the thickened wall of the dome to some extent which apparently did not reach the neck. These aneurysms were successfully neck clipped. The third patient showed marked thickening of the wall, which may be associated with thrombosis, which extended to the neck. Intraoperative findings of the aneurysm wall were compatible with these factors, and removal of atherosclerotic plaque and thrombus from the neck and dome of the aneurysm was necessary before successful neck clipping.

　The HRT2WI may contribute to a better surgical strategy for large aneurysms which may have wall thickening.