Natural History and Annual Rupture Rate of Small Unruptured Intracranial Aneurysm: SUAVe Study, Japan: An Interim Report

Abstract

We started a prospective study on the natural history of small unruptured intracranial aneurysms 3 years ago. Three hundreds forty aneurysms (294 cases) under 5 mm in diameter were registered and followed. At present, we had two cases with ruptured aneurysms. The annual rupture rate was 1.0% (95%CI: 0.2∼3.8%) in the period of 242 person/years. Both cases had multiple aneurysms. The annual rapture rate was 2.3% (95%CI: 0.6∼9.1%) in the cases with multiple aneurysms. On the other hand we had enlargement of aneurysm size in 13 cases (15 aneurysms). Five of 15 aneurysms were operated on for enlargement over 2 mm or bleb. Considering of this factor, the annual rupture rate will be higher. The risk factors of rupture and enlargement of aneurysm were female, aged patient, multiple aneurysms and anterior communicating and basilar aneurysm. We don't have any cases with ruptured aneurysms in single aneurysm-type or under 70 years old during this follow-up.