An arteriovenous malformation (AVM) is a congenital blood vessel defect that changes the way blood circulates though a particular area in the brain. Arteries and veins that fail to develop correctly form a cluster that prevents blood from flowing to nearby tissue. A brain AVM typically forms early in fetal development, though doctors are unsure of the exact causes. An AVM does not cause any noticeable symptoms in most cases, though it could potentially rupture if blood pressure gets too high, which can lead to extensive hemorrhaging and related complications. A ruptured brain AVM is a medical emergency that requires surgical drainage and repair to prevent a life-threatening situation.
Arteries normally deliver blood from the heart to hundreds of small capillaries in the brain, which in turn nourish brain tissue. Used blood is then drained through veins and directed back to the heart so it can be re-oxygenated. In the case of a brain AVM, arteries and veins are massed together, causing blood to run directly into veins without reaching brain tissue. A brain AVM is usually small enough that the majority of blood flow still passes through the brain correctly.
Researchers have been unable to identify clear causes or risk factors for brain AVM development. There does not appear to be a genetic component, as the problem only rarely runs in families. Environmental factors, such as a mother's diet, medication use, or lifestyle activities have also not been linked to the condition.
Most small brain AVMs do not cause health problems. It is possible, however, for a child or young adult to experience frequent migraines or seizures that are later connected with AVMs. A small number of older people who have unruptured, undiagnosed malformations develop rapidly declining vision, memory, and concentration abilities as well. Hemorrhaging is the major concern with a brain AVM, which can lead to a debilitating headache, vision loss, numbness, and problems speaking and breathing.
A brain AVM may go undiagnosed until it is discovered during tests for other problems, such as seizure disorders. If imaging scans reveal a small AVM, a neurologist may decide to perform a preventive surgery. A small piece of skull is removed during surgery and the AVM is excised with a laser device. Another option that is growing in popularity is called endovascular embolization, which involves delivering a type of glue to the AVM to seal it and prevent blood flow.
Emergency surgery is vital in treating a ruptured brain AVM. While the patient is given life-supporting oxygen and heart stabilizing therapy, the AVM is quickly removed and excess blood is drained with a vacuum tube. The prognosis after surgery depends on the amount of damage incurred, but many patients are able to make full recoveries with additional surgeries and physical therapy.