An arteriovenous malformation (AVM) in the brain is a relatively rare condition – occurring in less that 1 percent of the population. It can, however, be neurologically morbid in young adults ages 15 to 20, who are at the greatest risk for hemorrhage and least likely to exhibit symptoms. About 2 to 4 percent of all AVMs each year hemorrhage.
An AVM’s tangled mass of blood vessels, which forms in utero, produces multiple direct connections between arteries and veins without the normal, intervening capillaries. Symptoms often are not present until later in life or until after the AVM ruptures.
A small number of congenital syndromes, such as Sturge-Weber, Rendu-Osler-Weber, ataxia telangiectasia, and Wyburn-Mason, are associated with AVMs. Once formed, extrinsic factors, such as arterial shunting, growth factors and intracranial hemorrhage, may alter the size and shape of an AVM.
The most common types of AVMs are: