Reviewed by Brian R. Robinson, MDArteriovenous Malformation (AVM) is a congenital condition. AVM can occur in the brain, brain stem, or spinal cord, and involves the improper connection of arteries and veins. The cause of the abnormalities is unknown, and the condition develops in a different manner in each person.
In an AVM, the arteries and veins grow in a tangled web, and often this tangle of circulatory pathways forms a blood-filled sac in the brain that can bleed easily. In about 50% of people with AVM, the mass of arteries and veins will result in blood leaking into the subarachnoid space, the fluid-filled space between the inner and outermost meninges (thin membranes covering the brain). The condition occurs with equal frequency in men and women.
