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. Most believe: 2-4% per year. 3, spontaneous improvement. Rare. In a review of 700 cases, a total of 6 cases (0.9%) were found to have lesion disappearance 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; a, the current mainstream view is that small AVMs have a relatively low risk of bleeding while large AVMs have a higher risk of bleeding; b, yet a small number of studies have associated small AVMs with an elevated risk of bleeding. 3, deep venous drainage; 4, only a single draining vein; 5, restricted venous drainage (venous stenosis or regurgitation); 6, subscreen AVM; 7, lesion in the deep brain; 8, periventricular; 9, presence of intracranial aneurysm; 10, involvement of a perforating branch of the MCA in the blood supply; 11, presence of aneurysm in a non-vascular nest; 12, advanced age; 13, women of childbearing age. Outcome after hemorrhage The overall mortality rate after AVM hemorrhage is lower than that of hemorrhage due to other intracranial disorders. This is partly due to the fact that AVMs are congenital disorders and the adjacent brain tissue is adapted to the presence of the lesion 1. Mortality from hemorrhage 5% - 30%; 2. Morbidity from hemorrhage 20% - 30%.