Unruptured Intracranial Aneurysms in the Norwegian Nord-Trondelag Health Study (HUNT): Risk of Rupture Calculated From Data in a Population-based Cohort Study

BACKGROUND: Rupture risk of unruptured intracranial aneurysms (UIAs) has been investigated in studies observing the natural history of this condition. Such studies have been prone to selection bias that may influence the results. OBJECTIVE: To calculate the overall rupture risk from data on the prevalence of UIA, which constitutes the population at risk, and the incidence of aneurysmal subarachnoid hemorrhage (aSAH) in the same population. METHODS: Data were collected from the Norwegian Nord-Trondelag Health Study (HUNT), a large population-based cohort study. The prevalence of UIAs was estimated by performing magnetic resonance angiography in 1006 randomly selected volunteers 50 to 65 years of age from this population cohort. The incidence of aSAH was investigated by searching national and hospital registers with thorough case ascertainment to avoid inclusion of nonaneurysmal subarachnoid hemorrhage. RESULTS: The prevalence of UIAs was 1.9% and incidence of aSAH was 16.4 per 100 000 person-years. Based on these figures, the overall rupture risk in the 50-to 65-year age group in the HUNT population is 0.87% per year. CONCLUSION: This is the first study to estimate rupture risk of intracranial aneurysms from epidemiologic data in a large population-based cohort. This study design is less prone to selection bias and may provide an important supplement to the existing literature of studies of natural history of UIAs.