We investigated 235 cases of unruptured cerebral aneurysms experienced in the past 9 years. There were 117 operated and 118 unoperated cases. The decision to operate was made by the patients, who were informed that the rupture rate of the discovered aneurysms was 0.5-1.0% and surgical risks were about 5%. Observation was started just after the operation for operated cases and after radiological investigation was confirmed for the unoperated cases. A Rankin scale of II or worse was considered morbidity. Aneurysms were grouped according to the aneurysm size (small, below 5 mm; medium, 5-15 mm; large, over 15 mm). Surgical mortality was 0.9%, and morbidity was 2.7%. Surgical morbidity and mortality increased according to aneurysm size. The rupture rate of the unoperated cases increased as aneurysm size increased. The annual rupture rate of the small group was 0.4%, whereas the medium group was 6.4% and the large group was 11.4%. The rate of subarachnoid hemorrhage after treatment of the unruptured cerebral aneurysms was 0.2% per year. Based on these data, we investigated 2 groups of unoperated and operated patients using the Kaplan-Meyer curve and Log-Rank test. Concerning mortality, the operated cases had a significantly better outcome than unoperated cases. When morbidity was included, no significant efficacy was noted. However, in the medium group (5-15 mm size), patients undergoing surgery showed significantly better outcome.
These results indicate careful selection of the treatment of unruptured cerebral aneurysm is necessary. Observation may be indicated especially when the aneurysm size is below 5 mm.
