Arteriovenous Malformation

An arteriovenous malformation (AVM) is an abnormal tangle of blood vessels that looks like a bird’s nest. The tangle is made of arteries that would normally provide blood to your brain and veins that would normally drain blood from brain tissue.

Blood moves through your body within an organized closed circuit of blood vessels. Your arteries carry oxygen-rich blood from your heart to your brain and to the rest of your body’s organs and tissues. Your veins return oxygen- and nutrient-poor blood and waste products from tissues back to your heart and lungs.

Normally, the exchange takes place in your capillaries, where the smallest blood vessel units of arteries and veins connect. If you have an AVM, the “bridge” of capillaries between your arteries and veins is missing. This causes high-flow arterial blood to connect directly to veins that aren’t used to high blood pressure. As a result, the abnormal connection between the artery and vein in an AVM can cause vessel rupture and bleeding into your brain.

Types of AVMs

The two types of AVMs are:

• Brain arteriovenous malformations. These develop anywhere within your brain tissue or on the surface of your brain. AVMs most commonly occur in your brain, brainstem and spinal cord.
• Peripheral arteriovenous malformations. These can form anywhere in your body’s 100,000 miles of blood vessels. They can happen on your face, arms or legs, and in tissues and organs like your heart, liver or lungs.

How common are arteriovenous malformations?

Arteriovenous malformations are rare. They’re present in about 1 in 100,000 people. Anyone can be born with an AVM. Providers mainly discover them in people from ages 20 to 40. The risk of symptoms is highest between ages 30 and 50.