An arteriovenous malformation (AVM) is an abnormal tangle of blood vessels connecting arteries and veins, which disrupts normal blood flow and oxygen circulation.
Arteries are responsible for taking oxygen-rich blood from the heart to the brain. Veins carry the oxygen-depleted blood back to the lungs and heart.
When an AVM disrupts this critical process, the surrounding tissues may not get enough oxygen. Also, because the tangled blood vessels that form the AVM are abnormal, they can weaken and rupture. If the AVM is in the brain and ruptures, it can cause bleeding in the brain (hemorrhage), stroke or brain damage.
The cause of AVMs is not clear. They're rarely passed down among families.
Once diagnosed, a brain AVM can often be treated successfully to prevent or reduce the risk of complications.
Symptoms of AVM vary based on where it's located. Often the first signs and symptoms appear after bleeding occurs. Besides bleeding, signs and symptoms can include:
- Progressive loss of neurological function
- Nausea and vomiting
- Loss of consciousness
Other possible signs and symptoms include:
- Weak muscles
- Paralysis in one part of the body
- Loss of coordination that can cause problems with gait
- Problems performing tasks that require planning
- Weakness in the lower extremities
- Back pain
- Vision problems, including losing part of your field of vision, loss of control of eye movements, or swelling of part of the optic nerve
- Problems with speech or understanding language
- Unusual sensations including numbness, tingling or sudden pain
- Memory loss or dementia
Children and teens may have trouble with learning or behavior.
One type of AVM called a vein of Galen defect causes symptoms that appear at or shortly after birth. A vein of Galen defect is located deep inside the brain. Signs can include:
- A buildup of fluid in the brain (hydrocephalus) that causes enlargement of the head
- Swollen veins on the scalp
- Failure to thrive
- Congestive heart failure
When to see a doctor
Seek medical attention if you have any of the signs and symptoms of an AVM, such as headaches, dizziness, vision problems, seizures and changes in thinking or neurological function. Many AVMs are currently discovered incidentally, often after a CT scan or an MRI is obtained for reasons not directly related to the AVM.
AVMs result from development of abnormal direct connections between arteries and veins, but experts don't understand why this happens. Certain genetic changes might play a role, but most types are not usually inherited.
Rarely, having a family history of AVMs can increase your risk. But most types of AVMs aren't inherited.
Certain hereditary conditions may increase your risk of AVM. These include hereditary hemorrhagic telangiectasia (HHT), also called Osler-Weber-Rendu syndrome.
The most common complications of an AVM are bleeding and seizures. If left untreated, the bleeding can cause significant neurological damage and be fatal.