Normally, arteriescarry blood containing oxygen from the heart to the brain, and veinscarry 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.
All blood vessel malformations involving the brain and its surrounding structures are commonly referred to as AVMs. But several types exist:
Physicians do not categorize states of arteriovenous malformation (AVM) as it is not a progressive disease. The condition is congenital – occurring at birth – and continues through life unless treated. In many cases, symptoms never appear and the person leads a normal life unaware of the condition. However, an AVM can grow, creating pressure on surrounding areas of the brain, leading to headaches, dizziness and confusion. In addition, the AVM can reach a stage of development where it may burst.
The symptoms of arteriovenous malformation (AVM) vary widely, affecting different individuals to varying degrees. Most people with AVM experience very few or no symptoms. Their condition often becomes apparent only during treatment for an unrelated problem or during an autopsy. If no symptoms appear by the time a person is in their late 40s or early 50s, the AVM is likely to be stable and not cause any problems. However, about 12 percent of people with AVM experience symptoms vary in type and degree. Pregnancy may cause an onset or increase in symptoms related to changes in blood pressure. Some people may experience seizures throughout their lives and suffer permanent damage to the brain and central nervous system. The condition is fatal in about 10 percent of cases where extensive bleeding occurs. The first symptoms of AVM are those usually associated with a stroke, caused by blood leaking into surrounding brain tissue, occurring in 2 to 4 percent of all AVMs. Hemorrhages may occur at any time throughout a person’s life, but most often affect people in their mid to late teens.
A number of signs may indicate an AVM that has not bled:
Neuroscience offers several treatment options for arteriovenous malformation (AVM). Symptoms such as headache and seizures may be alleviated with medication, but due to the potential danger of hemorrhage, leaving the AVM itself untreated carries some level of risk. The most common treatment option for an AVM is surgical intervention; however, surgery on the central nervous system always carries risks that the doctor will weigh carefully against the benefits in advising the patient
Brain AVMs occur in less than 1 percent of the general population. It’s estimated that about one in 200–500 people may have an AVM. AVMs are more common in males than in females.
We don’t know why AVMs occur. Brain AVMs are usually congenital, meaning someone is born with one. But they’re usually not hereditary. People probably don’t inherit an AVM from their parents, and they probably won’t pass one on
to their children.
Brain AVMs can occur anywhere within the brain or on its covering. 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 and circulate the cerebrospinal fluid).
Most AVMs don’t grow or change much, although the vessels involved may dilate (widen). Some AVMs may shrink due to clots in part of the AVM. Some may enlarge to redirect blood in adjacent vessels toward an AVM.
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. Eventually they may burst from the high pressure of blood flow from the arteries, causing bleeding into the brain.
The chance of a brain AVM bleeding is 1 percent to 3 percent per year. Over 15 years, the total chance of an AVM bleeding into the brain — causing brain damage and stroke — is 25 percent.
The risk of recurrent intracranial bleeding is slightly higher for a short time after the first bleed. In two studies, the risk during the first year after initial bleeding was 6 percent and then dropped to the baseline rate. In another study, the risk of recurrence during the first year was 17.9 percent. The risk of recurrent bleeding may be even higher in the first year after the second bleed and has been reported to be 25 percent during that year. People who are between 11 to 35 years old and who have an AVM are at a slightly higher risk of bleeding.
The risk of death related to each bleed is 10 percent to 15 percent. The chance of permanent brain damage is 20 percent to 30 percent. 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 on how much blood has leaked from the AVM.