喫煙が未破裂脳動脈瘤の発生およびくも膜下出血の発症におよぼす影響

Cigarette Smoking Increases the Risk of Developing a Cerebral Aneurysm and of Subarachnoid Hemorrhage

I．はじめに

　喫煙は血管の動脈硬化を促進し脳卒中のリスクを増加させる^{2,14,17,21）}．なかでも喫煙とくも膜下出血との関連性はmeta analysisでみると脳出血や脳梗塞に比べさらに強く，喫煙者のくも膜下出血の発症は非喫煙者の29倍となる^14）．Weir（1998）らのcooperative studyでは，喫煙者のくも膜下出血の発症率の上昇に加え，発症率と喫煙量が比例し，脳血管攣縮を合併する率が非喫煙者にくらべより高いという結果になった^20）．一方，くも膜下出血の原因となる脳動脈瘤がどう形成され破裂するかについては，hemodynamic factorや，中膜欠損，高血圧の影響など複数の要因が提唱されている^7,11,18）が，喫煙がどう影響するかのメカニズムについてはいまだに解明されていない．また喫煙が動脈瘤の形成に関与するのか，破裂に関与するのかも明確ではない．今回くも膜下出血例および未破裂脳動脈瘤症例について，脳ドック受診者で動脈瘤が否定された症例をコントロールとし喫煙率の違いについて調査した．本研究の結果について喫煙が動脈瘤の形成や破裂に及ぼす影響について文献的考察を加え検討した．

Despite recent advances in diagnostic and therapeutic techniques, subarachnoid hemorrhage (SAH) isstill a serious condition associated with high mortality and morbidity. There are no effective treatmentsother than surgical intervention. However, another option for decreasing the occurrence of SAH may beprevention of aneurysms formation and of their rupture by controlling risk factors. Cigarette smoking hasbeen recently shown to be one of the major risk factors for SAH.

We investigated whether cigarette smoking increased the risk of developing cerebral aneurysms and ofSAH. Degree of smoking was investigated in 182 patients with SAH and in 123 patients with an unrup-tured cerebral aneurysm incidentally detected (luring investigation of other diseases. Sixty-nine patientswith other diseases who were shown to be free of cerebral aneurysms through MR angiography served ascontrols. Smoking significantly increased the risk of both aneurysm formation and SAFI : The odds ratiofor SAH was 2.4, and for unruptured cerebral aneurysm 1.7. Smoking especially increased the occurrenceof SAH in women and in youngsters. However, smoking did not influence the occurrence of cerebral vaso-spasm and multiplicity of aneurysms. These data suggest the importance of avoiding smoking to preventthe occurrence of cerebral aneurysms and of SAH.