Natural course Estimated annual AVMs bleed at a rate of <2% - 18.7% per year. the risk of bleeding in AVMs strongly depends on the presence or absence of a previous history of bleeding. 1. previous history of bleeding The most commonly reported rebleeding rate in the first year of bleeding is approximately 7%. Other studies: 3.9 %, 17.9 %, 17.8 %. After 3-5 years, the risk of bleeding decreases to baseline values. 2, no previous history of bleeding Mostly considered: 2-4% per year 3, spontaneous improvement Rarely, in a review of 700 cases, a total of 6 cases (0.9%) were found to have lesions that disappeared on imaging follow-up. Three of these cases were complete regression after partial resection. Risk of intra-survival bleeding Assuming a constant annual risk of bleeding of 2% - 4%, the following equation section calculates the risk of intra-survival bleeding Intra-survival risk = 1 - (risk of not bleeding) ~ [years of survival remaining] or assuming an annual risk of 3%, the survival risk is approximated as: intra-survival risk = 105 - patient age Risk factors for bleeding In the AVM patient population, the risk of bleeding is not the same. The risk of bleeding varies widely depending on many patient characteristics. However, care should be taken when interpreting data on bleeding risk factors. Because almost every factor associated with bleeding in AVMs can be found in more than one article that does not have a significant correlation. 1. previous bleeding history a strong predictor of future bleeding 2. size of AVM ------ views are inconsistent (1) The prevailing view is that small AVMs have a relatively low risk of bleeding, while large AVMs have a high risk of bleeding. (2) However, a few studies have suggested that small AVMs are associated with an increased risk of bleeding 3. deep venous drainage 4. single draining vein only 5. restricted venous drainage (venous stenosis or regurgitation) 6. submural AVM 7. lesion in the deep brain 8. periventricular 9. presence of intracranial aneurysms 10. involvement of MCA penetrating branches in blood supply 11. presence of aneurysms in non-vascular nests 12. advanced age 13. women of childbearing age Bleeding Outcome after AVM bleeding The overall mortality rate after AVM bleeding is lower than that of bleeding due to other intracranial diseases. Because partly due to the fact that AVMs are congenital diseases, the adjacent brain tissue is also adapted to the presence of the lesion 1. Mortality rate of hemorrhage 5% - 30% 2. Morbidity of hemorrhage 20% - 30%