An arteriovenous malformation of the brain (AVM) is a tangle of arteries and veins, which short-circuits healthy blood flow. Blood which normally is pumped through arteries then through smaller vessels called capillaries, is instead sent back through the veins to the heart.
Nourishment of the tissues with oxygenated blood should take place within the capillaries but an AVM has no capillaries. Tissues nearby an AVM can therefore be starved from oxygen deprivation.
AVMs can occur in many places in the body, but they are predominantly found in the brain or the spine. We will concern ourselves here with the ones that occur in the brain.
The cause of arteriovenous malformations of the brain is unknown. They are usually formed congenitally, or before birth.
A person with an AMV might not experience any symptoms throughout their lives, or they may at some point experience headaches or seizures, or symptoms that are much more serious, some of them quite dangerous.
Large AVMs can put pressure on the brain, causing neurological problems that can become progressively more severe. Blood vessels can rupture, resulting in a hemorrhage, or bleeding in the brain.
If a hemorrhage should occur, symptoms may resemble those which are brought on by a stroke. These symptoms may include severe headache of a sudden onset, difficulty in speaking, an inability to understand the words spoken by others, visual disturbances, vomiting, weakness, numbness and unsteadiness.
A hemorrhage is most likely to occur in people between the ages of 15 and 20, though this can also happen later in life. A hemorrhage can be a life-threatening condition and requires immediate medical attention.
An arteriovenous malformation of the brain can bring on other complications.
An aneurysm may develop due to pressure on blood vessel walls, and there is a risk that it may rupture.
Some AVMs will grow bigger, involving more arteries. This can can move or put pressure on the brain. The cerebrospinal fluid (protective fluids which need to flow freely around the brain, acting as a shock absorber) can be restricted.