未破裂脳動脈瘤非手術例の経過観察よりみた動脈瘤の易破裂性

Natural History of Unruptured Cerebral Aneurysms of the Unoperated and Observed Cases

Ⅰ．はじめに

　くも膜下出血は血管内手術や脳血管攣縮に対する様々なアプローチにもかかわらず，いまだに死亡率が高い疾患である^10,26)．近年画像診断の進歩や脳ドックにより未破裂脳動脈瘤が発見される機会が多くなった^19,23,30)．一方未破裂脳動脈瘤の治療については，手術合併症は少なくなく¹⁷⁾，適応を決める際，手術しなかった場合の自然歴を知ることが最も重要となる．しかしながら，自然歴は従来の報告では手術しなかった症例を対象にした追跡調査がほとんどで^{1,3,4,16,28,29,31,32)}，経過観察をした対象症例の背景が異なるため様々な異なる破裂率が報告され，いまだ一定の結論に達していない^{1,3,4,13,16,28,30-32)}．今回われわれは，発見されたものの手術しなかった未破裂脳動脈瘤をprospectiveに過去9年間調査し，破裂率について背景を含めて検討し，従来の報告と比較し手術適応を考えるうえでの問題点を考察した．

Purpose: Natural history of unruptured cerebral aneurysms is still a matter of discussion. In this study,we investigated the prognosis of unruptured cerebral aneurysms of unoperated cases in a prospective design.

　Methods: Between September, 1992 and December, 2001,we have encountered a 256 cases of unruptured cerebral aneurysms. Among them, 118 cases were observed and were checked every year for their status. The endpoint was designed as their death and aneurysm rupture. Their rupture rate, mortality due to aneurysm death,and the cause of death other than aneurysm were investigated. Univariate analysis, chi-square test was used as statistics. A p-value less than 0.05 was considered as significant.

　Results: Annual rupture rate of unoperated unruptured cerebral aneurysms of size below 5 mm, between 5-15 mm, and over 15 mm increased according to the aneurysm size, 0.4 ％,3.3 ％ and 9.9 ％ respectively. The sole risk factor for the feasibility of rupture of unruptured aneurysms was their size （p＜0.001). Aneurysm related mortality, however, was high in posterior circulation aneurysms. In patients under 70 years of age, 45 ％ of patients died of cerebral aneurysms, but this rate decreased to 17 ％ for patients over 70 years of age.

　Conclusion: The rupture rate of unruptured cerebral aneurysms over 5 mm in size is not low. Unruptured aneurysms of the posterior circulation may have a much higher risk of rupture, so further investigation is necessary.