From the Cerebrovascular Imaging and Intervention Committee of the American Heart Association Cardiovascular Council
Randall T. Higashida, M.D., Chair
Normally, arteries carry blood containing oxygen from the heart to the brain, and veins carry blood with less oxygen away from the brain and back to the heart. When an arteriovenous malformation (AVM) occurs, a tangle of blood vessels in the brain or on its surface bypasses normal brain tissue and directly diverts blood from the arteries to the veins.
Normal Blood Vessels
Abnormal Connection of Blood Vessels
Brain AVMs occur in less than one percent of the general population. It is estimated that about one in 200-500 people may have an AVM. AVMs are more common in males than females.
We do not know why AVMs occur. Brain AVMs are usually congenital, meaning someone is born with one. However, they usually are not hereditary. People probably do not inherit an AVM from their parents, and they probably will not pass an AVM on to their children.
Brain AVMs can occur anywhere within the brain or on the covering of the brain. This includes the four major lobes of the front part of the brain (frontal, parietal, temporal, occipital), the back part of the brain (cerebellum), the brainstem, or the ventricles (deep spaces within the brain that produce the cerebrospinal fluid).
Most AVMs do not grow or significantly change although the vessels involved may dilate. There are some reported cases of AVMs shrinking or enlarging, but this may be due to clots in parts of an AVM causing it to shrink, or to redirecting adjacent blood vessels toward an AVM.
Symptoms may vary with location.
A brain AVM contains abnormal and, therefore, "weakened" blood vessels that direct blood away from normal brain tissue. These abnormal and weak blood vessels dilate over time and may eventually burst from the high pressure of blood flow from the arteries causing bleeding into the brain.
There is a 1-3 percent chance per year of a brain AVM bleeding. Over a 15-year period, there is a 25 percent total chance of an AVM bleeding into the brain, causing brain damage and stroke.
With one bleed, the chance of a second bleed is 25 percent over the next four years, or 6 percent per year. If there are two or more bleeds, the chance of more bleeds is even higher, increasing to 25 percent per year. Individuals with an AVM are at a slightly higher risk of bleeding between the ages of 11 and 35.
There is a 10-15 percent risk of death related to each bleed and a 20-30 percent chance of permanent brain damage. Each time blood leaks into the brain, normal brain tissue is damaged. This results in loss of normal function, which may be temporary or permanent. Some possible symptoms include arm or leg weakness/paralysis, or difficulty with speech, vision or memory. The amount of brain damage depends upon how much blood has leaked from the AVM.
If an AVM bleeds, it can affect one or more normal body functions, depending on the location and extent of the brain injury. Different locations in the brain control different functions:
Although all blood vessel malformations involving the brain and its surrounding structures are commonly referred to as AVMs, there are actually several types:
There are three kinds of dural fistulas.
The best treatment is usually endovascular surgical blocking of the abnormal connections that have caused the fistula. This involves guiding small tubes (catheters) inside the blood vessel and blocking off the abnormal connections with X-ray guidance. Depending upon the location and size, many of these can be treated and cured by these endovascular, less invasive techniques.
Most AVMs are detected on either a computed tomography (CT) brain scan or with a magnetic resonance imaging (MRI) brain scan. These tests are very good at detecting brain AVMs. They also provide information about the location and size of the AVM and whether it may have bled.
A doctor may also perform a cerebral angiogram. This test involves inserting a catheter (small tube) through an artery in the leg and guiding it into each of the vessels in the neck going to the brain, injecting contrast (dye) and taking pictures of all the blood vessels in the brain. For any type of treatment involving an AVM, an angiogram may be needed to better identify the type of AVM.
In general, an AVM may be considered for treatment if it has bled, if it is in an area of the brain that can be easily treated and if it is not too large.
This depends upon what type it is, the symptoms it may be causing, and its location and size.
The best course of treatment depends upon what type of symptoms the patient is having, what type of AVM is present, and the AVM's size and location.
Each of these specialists has had advanced training and is highly skilled at treating complex brain vascular malformations.
Stroke and cerebrovascular diseases are the third-leading cause of death and a leading cause of major disability in the United States. More than 700,000 new and recurrent strokes occur each year, resulting in over 167,000 deaths and more than 250,000 permanent disabilities. About 4.7 million stroke survivors are alive today.
Ischemic strokes occur when the normal blood flow to the brain is blocked. They account for the majority of strokes. Treatment is available but must be started as soon as possible to give the best chance for recovery.
Hemorrhagic strokes are caused by bleeding into the brain, resulting in either death or major disability. Many of these strokes occur when a cerebral aneurysm or brain AVM ruptures.
For more information, contact the American Stroke Association, a division of the American Heart Association, at 1-888-4-STROKE (1-888-478-7653) or visit StrokeAssociation.org.
Funded through an educational grant provided by Boston Scientific