Oxygenated blood in the arteries and deoxygenated blood in veins normally flow separately through the body. At the tissues, they each break up into a network of tiny capillaries where blood flow slows down, allowing the exchange of gases to and from the tissues. An arteriovenous malformation (AVM) is a tangled mass of abnormally formed blood vessels, where blood flows quickly and exchanges between arteries and veins, bypassing the tissues. AVMs are commonly seen in the brain and spine, but may develop anywhere in the body. It is unclear what causes arteriovenous malformations, but they are thought to occur during fetal development due to the absence of capillaries.
Symptoms are usually noticed between the age of 10 and 40, gradually building up until they stabilize in middle age, when they are less likely to cause symptoms. Brain arteriovenous malformations are occasionally associated with symptoms such as headache, numbness, muscle weakness or paralysis, confusion, severe unsteadiness, vision loss, difficulty speaking and seizures. Very often, symptoms do not show until the blood vessels weaken, bulge (aneurysm), rupture and bleed in the brain (hemorrhage), and can be life-threatening. A severe form of AVM, called vein of Galen defect, develops soon after birth and is characterized by fluid build-up and swelling in the head, seizures, swollen veins, congestive heart failure and failure to survive.
To diagnose a brain arteriovenous malformation, your doctor will review your symptoms and perform a physical examination. Imaging studies such as CT, MRI or cerebral arteriography (dye injected through your artery is detected through X-rays) are ordered to identify the AVM and its supporting vessels along with any associated hemorrhage or tissue damage.
Treatment depends on the size and location of the arteriovenous malformation. If you have few symptoms or the AVM is not easily accessible, your doctor may choose to monitor it. Medications may be prescribed to treat symptoms such as headache and seizures. In case of a rupture or severe symptoms, surgical resection may be performed by cutting through your skull and carefully removing the AVM after sealing its vessels. Deep AVMs may be treated with a minimally invasive procedure called endovascular embolization, which approaches the AVM through a vessel in your leg and plugs the AVM vessel with microcoils or a glue-like substance. Your doctor may also use stereotactic radiosurgery, which uses focused radiation to destroy the blood vessels of an AVM. This is useful for treating small and inaccessible arteriovenous malformations.