Annual risk for the first hemorrhage from untreated cerebral arteriovenous malformations.

To estimate the annual risk for the first hemorrhage, survival and life table statistics were used to analyze data from 2262 patients with cerebral arteriovenous malformations (AVM). We found that the risk for hemorrhage increases with increasing age. A validity test revealed, however, that life table statistics used on the total patient material underestimated the annual risk for hemorrhage, especially for patients 20-50 years of age. A method based on the fact that the distribution of the time at risk until the initial hemorrhage (= age at first rupture) reflects the risk for hemorrhage in untreated AVM was therefore also employed. The analysis yielded three conclusions: 1) the annual risk of hemorrhage increases with age; 2) small AVM are less prone to rupture; and 3) the risk of hemorrhage is higher in women during their fertile years as compared to males in the same age group. The risk related to age, AVM size and location assessed by survival statistics in the subgroup of patients with a known date for the initial hemorrhage gave similar results.