What Is an Arteriovenous Malformation (AVM)?
An arteriovenous malformation (AVM) is an abnormal connection between an artery (a blood vessel carrying blood from the heart out to the body) and a vein (a vessel returning blood to the heart).
It's a shortcut that lets blood flow from an artery to a vein without passing through tiny vessels called capillaries. That's important because oxygen and other nutrients can only pass from the blood into the body parts that need them in capillaries.
Blood that takes a shortcut through an AVM returns oxygen-rich blood to the heart instead of delivering it to the body where it's needed. That means some of the heart's work is wasted, so the heart has to work harder than usual. Large AVMs or multiple AVMs can waste so much of the heart's work that it cannot keep up.
What Are the Signs & Symptoms of an Arteriovenous Malformation (AVM)?
A child with an AVM may have these symptoms:
- a pink, red, or purple birthmark
- bleeding, which may be difficult to stop
- warmer skin over the AVM
- a pulse that's felt around the AVM
Many AVMs, especially those in the head, are not recognized until adulthood. AVMs in the head may cause:
- trouble with body movements or speech
- loss of strength or sensation
- vision problems
- loss of the ability to understand speech
Bleeding from an AVM can be hard to stop. Frequent bleeding may lead to anemia. Even small amounts of bleeding from an AVM inside the skull can be very dangerous. AVMs may grow larger and cause trouble by pressing on other parts of the body.
What Causes Arteriovenous Malformations (AVMs)?
Arteriovenous malformations and venous malformations are types of vascular malformations (also called vascular anomalies). These are problems that happen when blood vessels (capillaries, arteries, veins, or lymphatic vessels) don't develop as they should.
Doctors don't know what causes AVMs. Kids who have them are born with them, and an AVM might get larger as the child grows.
AVMs can happen with some genetic syndromes, including:
- Cobb syndrome: wine-colored birthmarks with AVMs in the spinal cord
- hereditary hemorrhagic telangiectasia (HHT): AVMs in the lungs, brain, and digestive tract
- Parkes Weber syndrome: multiple AVMs in one arm or leg; the affected arm or leg typically grows longer and larger than the same limb on the other side
- Wyburn-Mason syndrome (also known as Bonnet-Dechaume-Blanc syndrome): AVMs of the retina (the light-sensitive area in the back of the eye) and brain, sometimes involving part of the face
How Is an Arteriovenous Malformation (AVM) Diagnosed?
An AVM is often found during an exam because a pulse may be felt in its vessels. Then, other tools may be used to learn more about it and plan treatment, such as:
- an ultrasound, to determine how much blood is flowing through the AVM
- a CT scan or MRI, to see the AVM's size and how close it is to normal body parts
- an angiogram, to map of the AVM's blood vessels, which will help doctors plan how to block blood flow to it
- an MRA, or MRA angiogram, which combines the MRI and angiogram techniques to map the AVM without using X-rays. Similarly, a CT angiogram can be performed.
- a standard angiogram, which shows the arteries by putting dye into a long thin tube (catheter) in the vessel while taking an X-ray
How Is an Arteriovenous Malformation (AVM) Treated?
The right treatment for an AVM depends on its location, size, and how it affects the child.
Why treat an AVM?
When a child's heart must work harder than usual because of an AVM, prompt treatment is important to prevent permanent changes. An AVM also might be treated to improve pain, bleeding, or its appearance.
AVMs in the arms, legs, and body are easier to treat than AVMs in the head.
AVMs outside of the skull are treated with:
- embolization: using catheter-guided tools to permanently block the arteries leading to the AVM
- sclerotherapy: injection of a chemical into an AVM that shrinks the blood vessels
AVMs in the head are called intracranial AVMs and may be treated with embolization, surgery using radiation (radiosurgery), or surgery.
Embolization and sclerotherapy usually are done by interventional radiologists (doctors who specialize in minimally invasive, targeted treatments).
Treatment for an AVM depends on its location, size and the symptoms it causes. A small AVM that's not in the head may never need treatment, but it could change as a child grows. Some AVMs get bigger, so it's important to track its size and its effects on a child's health and activities.