The Natural Course of Unruptured Cerebral Aneurysms: Natural Course Analysis of the Unruptured Cerebral Aneurysm Study in Japan

Keywords: aneurysm, stroke, natural history, subarachnoid hemorrhage, hemorrhage

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     The natural course of individual unruptured cerebral aneurysm is not well-determined.
     This study aims to clarify the natural course of unruptured cerebral aneurysms and the factors influencing their rupture.
     From January 2001 through April 2004, we enrolled newly identified cases of unruptured cerebral aneurysms from 276 institutions. From the registry, we assessed prospective data on 5,720 patients with 6,697 saccular aneurysms, who initially presented with a modified Rankin scale of 0, 1 or 2.
     The results from periodic follow-up exams were also registered.
     There was a female predominance (68%) and most of the aneurysms were discovered incidentally (96%). The mean age in the series was 62.6 years Standard deviation 10. Most frequently, the aneurysms occurred in the middle cerebral arteries (35%) followed by the internal carotid arteries (34%). The mean size of aneurysms was 5.7mm. During the 11,660 aneurysm-year follow-up, documented ruptures occurred in 111 aneurysms, resulting in an annual rupture rate of 0.95% 95% Confidence Interval (CI); 0.79-1.15. Ruptures occurred more often in lesions larger than or equal to 7 mm (Hazard ratio by the Cox regression: 5.11 95% CI; 3.34-7.83), in the posterior and anterior communicating arteries (hazard ratio compared to middle cerebral aneurysms: 1.90 1.12-3.21 and 1.90 1.07-3.38, respectively) and if the aneurysm was associated with bleb formation (hazard ratio: 1.83 1.21-2.74).
     This is a retrospective study.
     This study documented that natural course of unruptured cerebral aneurysm is not uniform. 
     The natural course is influenced by the characteristics of aneurysms such as size, location and shape of the aneurysms.


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