Background and Purpose—Purpose of the present study is to evaluate the clinical outcome of endovascular treatment of unruptured intracranial aneurysms and to address the question of long-term stability and protection against future subarachnoid hemorrhage.

Methods—Retrospective analysis of all patients treated in a 12-year period (173 patients: age 26 to 76 yr, mean 52.2±10.8/202 aneurysms: size 3 to 50 mm, mean 10.0±8.3).

Results—The mortality was 0.5%; the overall morbidity was 3.5%. The most frequent complications were thromboembolic events (10.9%). Of these, 3.0% of patients suffered a stroke, leading to severe disability in 1 patient (0.5%). In 1 patient, the aneurysm ruptured during treatment, resulting in relevant neurological disability. Another patient suffered a fatal aneurysm rupture hours after treatment. The occlusion rate depended on aneurysm and neck size. Follow-up angiography revealed a decrease of the occlusion rate over time. This trend was obvious in all size categories and was most pronounced in giant aneurysms. In 3 patients (1.5%) with partially thrombosed giant aneurysms of the posterior circulation, embolization could not prevent later aneurysm rupture. There were no ruptures of any other aneurysms in the follow-up period (3.7±3.4 yr).

Conclusion—Endovascular treatment is a highly safe procedure with low intervention-related morbidity and mortality. Long-term data for nongiant aneurysms showed good protection against rupture in the observation period. In contrast, the risk of rupture for giant aneurysms of the posterior circulation was as high as expected in observational studies.