Neurological Surgery 脳神経外科38巻5号

2010年05月発行

総説

頚部頚動脈血行再建術後過灌流：update

著者： 小笠原邦昭¹

所属機関： ¹岩手医科大学脳神経外科

ページ範囲：P.417 - P.425

Ⅰ．はじめに

　頚部頚動脈分岐部の粥状動脈硬化性狭窄病変が脳梗塞の原因となることはよく知られた事実である．この発症メカニズムとしては，狭窄部に形成された血栓あるいは粥腫そのものが末梢に飛んでいって脳血管を突然閉塞させる場合（artery-to-artery embolism）と狭窄により末梢である脳血管の灌流圧が下がって脳血流が低下する場合（血行力学的脳虚血）の2つがある．これを予防するために行われるのが粥状動脈硬化を除去する内膜剝離術（carotid endarterectomy：CEA）である．この手術法は欧米の大規模研究でその脳梗塞予防効果が証明された外科治療であり¹⁾，本邦でも同病変の増加に伴い盛んに行われている．また，血管内手術手技の発達とともに粥状動脈硬化を強制的に潰す治療法である頚動脈ステント術（carotid artery stenting：CAS）が臨床の場に導入された．2008年4月から保険収載され，CEAと同等の治療効果が期待されている．

　CEAあるいはCASは，それを適応する上で明確な基準がある¹⁾．すなわち，手術合併症を症候性病変（6カ月以内に脳虚血症状を来している）では6％，無症候性病変（6カ月以内に脳虚血症状を来していない）では3％以内に抑えなければ，有効性はないという厳しい制限がある．それゆえ手術合併症の発症メカニズムを知り，これを予知することが重要である．

　CEAにしてもCASにしても，その手術脳合併症として問題となるのが術中脳梗塞と術後過灌流である．さらに術中脳梗塞の原因として，遮断による大脳半球虚血（血行力学的脳虚血）と頚部頚動脈手術部位からの塞栓（artery-to-artery embolism）に分けられる．その発生比率はCEAにおいては，大脳半球虚血：塞栓：過灌流＝15：55：30とされ²⁷⁾，CASでは大脳半球虚血による術後脳梗塞はさらに少なく，塞栓の比率が高くなる．いずれにしても，術中塞栓症と術後過灌流が最大の問題である．

　術後過灌流は「脳組織の需要をはるかに越えた脳血流の急激な術後の増加」と定義され，本邦を中心とした研究でその病態が明らかになりつつあり，いくつかの総説も著わされている^8,9,18)．本稿では，術後過灌流の脳組織に対する影響，発生メカニズム，予知，CEAとCASとの相違につき，これらの総説以降の最近の知見を概説する．

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