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Brain AVM (arteriovenous malformation)

A brain AVM (arteriovenous malformation) is an abnormal connection between arteries and veins. An AVM is usually congenital, meaning it dates to birth.

An AVM can develop anywhere in your body but occurs most often in the brain or spine. A brain AVM, which appears as a tangle of abnormal arteries and veins, can occur in any part of your brain. The cause isn't clear.

You may not know you have a brain AVM until you experience symptoms, such as headaches or a seizure. In serious cases, the blood vessels rupture, causing bleeding in the brain (hemorrhage). Once diagnosed, a brain AVM can often be treated successfully.

Symptoms Causes Risk factors Complications

A brain AVM (arteriovenous malformation) may not cause any signs or symptoms until the AVM ruptures, resulting in bleeding in the brain (hemorrhage). However, some people with an AVM may have symptoms other than bleeding that are related to the AVM.

An AVM may also be detected on a brain scan performed for reasons unrelated to the AVM.

Symptoms of a brain AVM include:

  • Seizures
  • A whooshing sound (bruit) that can be heard on examination of the skull with a stethoscope or may be audible if you have an AVM
  • Headache
  • Progressive weakness or numbness

Some people may experience more-serious neurological symptoms, depending on the location of the AVM, including:

  • Severe headache
  • Weakness, numbness or paralysis
  • Vision loss
  • Difficulty speaking
  • Inability to understand others
  • Severe unsteadiness

Symptoms may begin at any age, but you're more likely to experience symptoms between ages 10 and 40. Brain AVM can damage brain tissue over time. The effects slowly build up, sometimes causing symptoms in early adulthood.

Once you reach middle age, however, brain AVMs tend to remain stable and are less likely to cause symptoms.

Some pregnant women may have worsened symptoms. However, it's not clear that pregnant women are at greater risk of an AVM bleeding. More research is needed to determine the risk during pregnancy.

When to see a doctor

Seek immediate medical attention if you notice any signs or symptoms of a brain AVM, such as seizures, headaches or other symptoms. A bleeding brain AVM is life-threatening and requires emergency medical attention.

A brain AVM is an abnormal connection between arteries and veins in your brain. Doctors believe that a brain AVM develops during fetal development. Why this occurs in some babies and not others is unknown.

Normally, your heart sends oxygen-rich blood to your brain through arteries, which branch into smaller arterioles and subsequently to the smallest blood vessels (capillaries). Oxygen is removed from blood in the capillaries and used by your brain.

The oxygen-depleted blood then passes into small venules and then into larger veins that drain the blood from your brain, returning it to your heart and lungs to get more oxygen.

If you have a brain AVM, blood passes directly from your arteries to your veins via abnormal vessels. This disrupts the normal process of how blood circulates through your brain.

Anyone can be born with a brain AVM, but these factors may be a risk:

  • Being male. AVMs are more common in males.
  • Having a family history. Cases of AVMs in families have been reported, but it's unclear if there's a certain genetic factor or if the cases are only coincidental. It's also possible to inherit other medical conditions that predispose you to having vascular malformations such as AVMs.

Complications of a brain AVM include:

  • Bleeding in the brain (hemorrhage). Walls of the affected arteries and veins may become thin or weak. An AVM puts extreme pressure on these walls because no capillaries are available to slow down the blood flow. This may result in bleeding into the brain (a hemorrhage).

    A very small (microscopic) hemorrhage causes limited damage to surrounding tissues and is unlikely to produce noticeable symptoms. A larger hemorrhage, however, can cause brain damage. It is known as an intracerebral hemorrhage when bleeding occurs in the brain tissue.

  • Reduced oxygen to brain tissue. With an AVM, blood bypasses the network of capillaries and flows directly from arteries to veins. Blood rushes quickly through the altered path because blood isn't slowed down by channels of smaller blood vessels.

    Surrounding brain tissues can't easily absorb oxygen from the fast-flowing blood. Without enough oxygen, brain tissues weaken or may die off completely. This results in stroke-like symptoms, such as difficulty speaking, weakness, numbness, vision loss or severe unsteadiness.

  • Thin or weak blood vessels. An AVM puts extreme pressure on the thin and weak walls of the blood vessels. A bulge in a blood vessel wall (aneurysm) may develop and become susceptible to rupture.
  • Brain damage. As you grow, your body may recruit more arteries to supply blood to the fast-flowing AVM. As a result, some AVMs enlarge, which displaces or compresses portions of the brain. This may prevent protective fluids from flowing freely around the hemispheres of the brain.

    If fluid builds up, it can push brain tissue up against the skull (hydrocephalus).

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