Arteriovenous Malformations (AVMs)

An arteriovenous malformation (AVM) is a defect in the vascular system, the body's network of blood vessels. That network has three parts:

• arteries, which carry oxygen-rich blood from the heart to the tissues and organs;
• veins, which carry blood and waste products back to the heart;
• capillaries, tiny vessels linking the smallest arteries to the smallest veins.

In an AVM, arteries and veins form an abnormal tangle and connect to each other directly, with no capillaries in between.

Why it matters

Without capillaries, blood rushes from the arteries straight into the veins faster than normal. The tissue around the AVM then does not receive all the oxygen it normally would, and that shortfall can damage tissue and kill nerve cells and other cells. The fast flow also raises the pressure inside the arteries and veins, which can weaken them. A weakened vessel may leak or burst.

Causes

AVMs are rare, and their cause is unknown. Most people who have one were born with it, though an AVM can also appear soon after birth or later in life.

Symptoms

AVMs can form anywhere in the body but are most common in the brain or spinal cord, and symptoms depend on where the AVM is. Most people with an AVM in the brain or spinal cord have few or no major symptoms. The danger is that a weakened vessel bursts and spills blood into the brain — a hemorrhage. A severe hemorrhage can cause a stroke and brain damage.

When an AVM does cause symptoms, they can include:

• seizures
• headache
• pain where the AVM is
• vision problems
• muscle weakness
• trouble moving or speaking
• confusion
• dizziness
• loss of consciousness

Diagnosis

A health care provider will ask about symptoms and medical history and do a physical exam, which may include listening for a bruit — a whooshing sound made by blood rushing through the AVM's arteries and veins. The provider may also order imaging such as a CT scan, MRI, ultrasound or cerebral angiography. In cerebral angiography, a special dye is injected so that the brain's blood vessels show up on x-rays.

Treatment

The right treatment depends on where the AVM is, how big it is, the symptoms, the person's overall health and their risk of bleeding. Options include:

• Monitoring for signs of a higher risk of hemorrhage.
• Medicines to ease symptoms.
• Surgery, which may be done when the risk of bleeding is higher than usual. There are several kinds, and some people have more than one. Surgery carries risk, especially on the brain or spinal cord, so patients and providers need to weigh the benefits and risks together before deciding.

Sources

• MedlinePlus, National Library of Medicine: "Arteriovenous Malformations," drawing on the National Institute of Neurological Disorders and Stroke.