Causes

The cause of brain AVM is unknown, but researchers believe most brain AVMs emerge during fetal development.

Normally, your heart sends oxygen-rich blood to your brain through arteries. The arteries slow blood flow by passing it through a series of progressively smaller networks of blood vessels, ending with the smallest blood vessels (capillaries). The capillaries slowly deliver oxygen through their thin, porous walls to the surrounding brain tissue.

The oxygen-depleted blood then passes into small blood vessels and then into larger veins that drain the blood from your brain, returning it to your heart and lungs to get more oxygen.

The arteries and veins in an AVM lack this supporting network of smaller blood vessels and capillaries. Instead, the abnormal connection causes blood to flow quickly and directly from your arteries to your veins, bypassing the surrounding tissues.