Arteriovenous Malformation

An arteriovenous malformation is a rare tangle of blood vessels that creates abnormal connections between arteries and veins, disrupting normal blood flow and potentially causing serious complications, especially when it occurs in the brain or spinal cord.

Table of contents

• What is an arteriovenous malformation?
• How common are arteriovenous malformations?
• Symptoms
• Causes and risk factors
• How are AVMs discovered?
• Diagnosis
• Treatment options
• Living with an arteriovenous malformation

What is an arteriovenous malformation?

An arteriovenous malformation (AVM) is an abnormal tangle of blood vessels that looks like a bird’s nest. The tangle creates irregular connections between arteries and veins in your body^[1].

To understand what happens in an AVM, it helps to know how blood normally moves through your body. Your arteries carry oxygen-rich blood from your heart to all parts of your body. Your veins carry blood with less oxygen back to your heart and lungs. Normally, the exchange takes place in tiny blood vessels called capillaries, which connect arteries to veins and deliver oxygen to cells^[2].

In an AVM, the bridge of capillaries between arteries and veins is missing. This causes high-pressure blood from arteries to flow directly into veins, which are not used to handling such high blood pressure. Blood passes quickly from an artery to a vein, disrupting the usual blood flow and preventing surrounding tissues from receiving oxygen^[1].

Because the tangled blood vessels in an AVM do not form properly, they can weaken and burst. Over time, some AVMs get progressively larger as the amount of blood flow increases. If an AVM bursts, it can cause bleeding into surrounding tissue, which can lead to serious complications. In the brain, bleeding is known as a hemorrhage and can cause a stroke or brain damage^[1].

• Brain
• Spinal cord
• Face
• Arms
• Legs
• Heart
• Liver
• Lungs

AVMs can occur anywhere in the body. There are two main types. Brain arteriovenous malformations develop anywhere within brain tissue or on the surface of the brain. These are the most common location. Peripheral arteriovenous malformations can form anywhere in the body’s blood vessels, including on your face, arms or legs, and in tissues and organs like your heart, liver or lungs^[3].

How common are arteriovenous malformations?

Arteriovenous malformations are rare. They are present in about 1 in 100,000 people. Anyone can be born with an AVM. Healthcare providers mainly discover them in people from ages 20 to 40. The risk of symptoms is highest between ages 30 and 50^[3].

Most people are born with AVMs, although they can form later in life in some cases. The best available data suggests that AVMs have a 1 to 3 percent per year risk of bleeding once discovered^[5].

Symptoms

Many people with AVMs experience few, if any, significant symptoms. In most cases, people with AVMs in the brain or spinal cord may not have symptoms at all. Up to 15 percent of people with AVMs don’t have symptoms^[2][3].

Sometimes an AVM doesn’t cause symptoms and can be found while getting images for another health concern. Often the first sign you have an AVM is after it bleeds. About 50 percent of people with a brain AVM have a brain bleed as their initial symptom^[1][3].

When symptoms do occur, they can vary depending on where the AVM is located in the body. Symptoms of AVMs can be mild or severe and may include^[2][3]:

• Seizures with or without loss of consciousness. Seizures can be focused on a small part of the brain or widespread, involving convulsions, a loss of control over movement, or a change in the level of consciousness.
• Headache. Headaches can vary greatly in frequency, duration, and intensity, sometimes becoming as severe as migraines. Headache pain can occur on either one side of the head or on both sides.
• Muscle weakness or complete paralysis in one part of the body.
• Nausea and vomiting.
• Numbness or tingling sensation.
• Dizziness.
• Problems with movement, speech, memory, thinking, balance or vision.
• Mental confusion, hallucinations or dementia.
• Back pain that can be sudden and severe, or weakness in the lower body and legs to the toes.
• Shortness of breath during physical activity.
• Coughing up blood if the AVM is in the lungs.
• Abdominal pain.
• Lumps on arms or legs or the trunk.
• Pain and swelling.

A spinal AVM can lead to degeneration of nerve fibers within the spinal cord below the level of the AVM, causing widespread paralysis. AVMs located on the frontal lobe close to the optic nerve or on the occipital lobe may cause a variety of vision problems, including a loss of part of the visual field, inability to control eye movement, or swelling in a part of the optic nerve^[2].

Causes and risk factors

Scientists aren’t sure what causes arteriovenous malformations. The cause of AVMs is not clear. Most of the time, people are born with them, and they likely develop during fetal development in the womb. They are congenital, meaning present at birth^[1][3].

AVMs are not typically caused by anything someone did or didn’t do. Rarely, they are passed down in families. AVMs may be hereditary and run in families in rare cases^[1][3].

AVMs commonly become evident during childhood and are often exacerbated at puberty or with pregnancies^[10].

How are AVMs discovered?

Unruptured AVMs often cause no symptoms and are discovered accidentally after brain imaging for other reasons. Most malformations tend to be discovered only incidentally, usually during treatment for an unrelated condition or at autopsy^[2].

The most common first symptom caused by an AVM is bleeding in the brain. This occurs in 70 percent of people with symptoms. Patients whose AVMs bleed often have sudden onset of a severe headache, and may also have weakness, nausea, vomiting, neck stiffness or sensitivity to sound and light. In severe cases patients may progress to coma. Bleeding is associated with a 10 to 20 percent chance of death and a 10 to 20 percent chance of disability^[5].

Less commonly, the first symptom of an AVM is a seizure, which occurs in 25 percent of symptomatic cases. The average age of patients with seizure as a first symptom is 25 years. Headaches are common in patients with AVMs, with 5 to 15 percent of patients complaining of long-standing headaches before their AVM is detected. However, most people with chronic headaches do not have an AVM^[5].

Diagnosis

To diagnose an arteriovenous malformation, your healthcare professional reviews your symptoms and gives you a physical exam. Your healthcare professional may listen for a sound called a bruit. A bruit is a whooshing sound caused by blood quickly flowing through arteries and veins of an AVM. It sounds like water rushing through a narrow pipe. A bruit can interfere with your hearing or sleep or cause emotional distress^[12].

Tests commonly used to help diagnose AVM include^[8][12]:

• Cerebral angiography. This is the most detailed test to diagnose a brain AVM and is considered the gold standard for imaging an AVM. Also called arteriography, this test uses a special dye called a contrast agent injected into an artery. A long, thin tube called a catheter is inserted into an artery in the groin or wrist. The catheter is threaded to the brain using X-ray imaging. The dye highlights the blood vessels to better show them on X-rays. The test reveals the location of the feeding arteries and draining veins, which is critical to planning treatment.
• CT scan (Computerized Tomography scan). These scans can help show bleeding. CT scans use X-rays to create images of the head, brain or spinal cord.
• CT angiography. This test combines a CT scan with an injection of a dye to help find an AVM that is bleeding.
• MRI (Magnetic Resonance Imaging). An MRI uses powerful magnets and radio waves to show detailed images of tissues. An MRI can pick up on small changes in these tissues.
• Magnetic resonance angiography (MRA). MRA captures the pattern and the speed and distance of blood flow through the irregular vessels.
• Transcranial doppler ultrasound. This test can help diagnose an AVM and tell whether the AVM is bleeding. The test uses high-frequency sound waves aimed at arteries to create an image of blood flow and its speed.

Treatment options

Treatment of an arteriovenous malformation depends on factors such as where the AVM is located, its size, your symptoms, your overall health, and your risk of bleeding. Once diagnosed, a brain AVM often can be treated to prevent or reduce the risk of complications^[1][6].

Treatment options may include^[6][9]:

• Monitoring and observation. Some brain AVMs are best left untreated after careful expert review. These are observed by yearly imaging and clinical follow-up. Medications are prescribed to manage symptoms if necessary, such as seizures or headaches. This option may be chosen when attempts to treat the AVM with other means may pose more risk of harm to the patient than the AVM itself.
• Surgical treatment (also called Open Microvascular Neurosurgery). Surgery requires opening the skull, known as a craniotomy, in order to remove the AVM. Specialized techniques using a microscope are used to remove the AVM from the spinal cord or brain. The advantage is that the AVM is then considered cured. In order for surgery to have any benefit, the entire AVM must be removed.
• Endovascular embolization. This technique is performed by specialized doctors. The purpose of this procedure is to prevent blood flow to the AVM. A catheter is used to insert a glue-like substance into the blood vessels. This AVM treatment option is used in conjunction with surgery or as a stand-alone treatment.
• Stereotactic radiosurgery (SRS), or Gamma Knife Treatment. This uses highly focused radiation that targets and intentionally damages blood vessels of the AVM. These damaged vessels produce scar tissue, which eventually seals off the brain AVM over time. While it is called radiosurgery, no incision is made. This treatment is usually for small, deep brain AVMs.

In some cases, more than one type of treatment may be used. The goal of any AVM treatment is to either cure the AVM or reduce its impact. Making the decision for brain surgery for AVMs is complex. Healthcare providers consider the risk of leaving it untreated while balancing the risks of different treatment methods^[9].

Living with an arteriovenous malformation

Although the outlook for brain AVM patients is generally positive, risks do exist. While living with an AVM may be difficult, knowing that you have support is very important. An AVM rupture can be life threatening, but early evaluation and proper treatment will help ensure the best possible outcomes. In fact, with prompt expert medical care, most people with AVMs can live active lives^[15].

Many individuals with an AVM can expect to live full and healthy lives following a diagnosis. Fortunately, if AVM treatment is necessary, current surgical treatment methods are safer and more effective than ever. Staying on top of your medical care and regularly speaking with your physician is extremely important in managing this condition^[15].

By taking care of yourself physically and emotionally, including a healthy diet and regular exercise, you will be able to remain an active and informed participant in your care and treatment. Some individuals have found that through gaining a better understanding of brain AVMs and their impact, there is a renewed sense of empowerment and hope. Those with an AVM may also benefit from speaking with counselors, therapists or support groups^[15].