A comparison of risk factors in the etiology of mirror and nonmirror multiple intracranial aneurysms

BACKGROUND: Pure mirror intracranial aneurysms represent a subgroup of multiple aneurysm patients where a congenital predisposition may play a major etiologic role. The aim of this study was to compare the pattern of prevalence of known risk factors for aneurysm disease between pure mirror and pure nonmirror multiple aneurysm populations. METHODS: Clinical records of all patients with multiple intracranial aneurysms admitted to our institution between January 1985 and September 2001 were reviewed. Age, localization of aneurysms, gender, and history of cigarette smoking or hypertension were noted and compared using Fisher's exact test and logistic regression analysis. RESULTS: There were 33 patients presented with pure mirror aneurysms (MirAn) and 49 with nonmirror multiple aneurysms (nMirAn). Average age of rupture occurred in the 5th decade in both groups. Female:male ratio was 3.1:1 in MirAn; 2.1:1 in nMirAn. In MirAn patients younger than 40 years it was 1:1. Smoking was the most prevalent risk factor in nMirAn (59.2%). In MirAn this was true only for patients in the 5th or 6th decades (65%), and hypertension was the most prevalent risk factor over that age (62.5%). A total of 80% of mirror aneurysm patients under 40 years had no known extrinsic risk factor, compared with 20% in nMirAn (p < 0.05). CONCLUSIONS: Differences in the relative prevalence of risk factors between both groups supports the hypothesis of a different etiologic process occurring in mirror aneurysm disease. Early rupture in patients with no extrinsic risk factors lends support to the role of a congenital predisposition over degenerative causes in these patients.