Purpose Annual bleeding rate of unruptured cerebral aneurysms have been reported relatively low. Indication of treatment for these patients is controversial. Results of long-term follow-up of unruptured aneurysms without treatment are analysed in comparison with coiled unruptured aneurysms.

Material and Method 917 patients with unruptured cerebral aneurysm were included in this study. All the patients were referred to single physician over the past 12 years. Indication of endovascular treatment was decided according to aneurysm size, shape, location, and family history of SAH. 661 patients selected observation and 256 patients endovascular treatment. In observation group MRA was repeated every 6–12 months. When MRA disclosed aneurysm growth, treatment is considered. In treated group angiography was performed year after treatment and MRA was repeated every year afterwards.

Results Follow-up was performed from 6–144 months, with average follow-up period 39.7 months (6-144) in observation group and 76.5 months in treated group respectively.

Aneurysm rupture occurred in 15 patients in observation group (2.1%). Final outcome of ruptured patients is GR 3 cases (20.0%), MD 2 (13.3%), SD 4 (26.7%), Dead 6 (40.0%). Annual bleeding rate is 0.7%. Rupture rate is higher (1.0%) in aneurysms over 10mm in diameter. In 7 patients aneurysm growth is observed in follow-up and aneurysms were treated with good results. In treated group results are GR 249 cases (97.3%), MD 3 (1.2%), SD 2 (0.8%), Dead 2 (0.8%) respectively. Kaplan- Meyer survival rate of both groups are similar without significant difference.

Conclusion Observation has better outcome in unruptured small cerebral aneurysms. 2. Treatment is indicated when aneurysm growth is detected in follow-up.

Disclosures S. Nemoto: None.