Arteriovenous malformations (AVM) are tangles of abnormal blood vessels. Arteriovenous malformations can form wherever arteries and veins exist. However, the ones that form in the brain or spinal cord can have especially severe effects.

Blood flows through arteries, bringing oxygen from the heart to the brain. The veins carry blood away from the brain to smaller blood vessels. These blood vessels slow the blood flow and allow oxygen to be delivered to the surrounding tissue.

Arteries in arteriovenous malformations don’t follow this pattern. They dump blood directly into veins through a channel called a fistula, an abnormal tube-like opening. The blood flow through this fistula is extremely fast. Complications from this include:

• Uncontrolled flow that doesn’t allow oxygen to be delivered

• Extreme blood flow puts a great deal of pressure on the wall of the blood vessels and may cause them to rupture and bleed (hemorrhage)

Two to four percent of all arteriovenous malformations hemorrhage or bleed. The damage caused by the bleeding depends on where the arteriovenous malformation is located. When the blood from the hemorrhage goes into the brain, brain tissue can be damaged temporarily or sometimes even permanently.

Arteriovenous malformations can seriously damage the brain and the spinal cord by:

• Reducing the amount of oxygen reaching the brain

• Causing bleeding (hemorrhage) into the tissues that make up the neurological system (the nervous system, including the brain and spinal cord)

• Pressing against or moving parts of the brain or spinal cord

Complications of arteriovenous malformations include strokes (blood supply and oxygen are totally cut off from the brain), hydrocephalus (excessive buildup of fluid within the brain), and spinal cord injury (possibly causing paralysis).

The sooner arteriovenous malformations are treated, the better the outcome. If you suspect you have this condition, contact your doctor immediately.

Causes

The cause of arteriovenous malformations is unknown. However, researchers believe that they occur as a fetus is developing and the arteriovenous malformations are present when you are born.

Arteriovenous malformations are most likely not hereditary (inherited from your parents), and, if you have an arteriovenous malformation, you will most likely not pass it on to your children.

Risk Factors

Arteriovenous malformations of the brain and spinal cord affect approximately 300,000 Americans. They occur equally in males and females and in all ethnic or racial backgrounds.

A risk factor is something that increases your chances of getting a disease or condition.

The following factors increase your chances of developing arteriovenous malformations. If you have any of these risk factors, tell your doctor:

• Age

• • Although symptoms can appear at any age, you are more likely to notice symptoms of arteriovenous malformations when you are in your 20s, 30s, or 40s.

• • Individuals with arteriovenous malformations are most likely to experience hemorrhaging (bleeding) between the ages of 11 and 35.

• • Children are more likely to hemorrhage from an arteriovenous malformation than adults. Arteriovenous malformations account for 30%–50% of hemorrhagic strokes (sudden bleeding in the brain) in children.

• Pregnancy

• • When you are pregnant, there is an increased amount of blood circulating in your system and an increase in your blood pressure. Symptoms of arteriovenous malformations may worsen when you are pregnant.

• Previous Hemorrhaging

• • If you have had bleeding (hemorrhaging) before, you are more likely to hemorrhage again within the first year since the hemorrhage.

Symptoms

There are a number of symptoms that you may experience if you have an arteriovenous malformation. Which symptoms you may or may not experience vary from person to person. They also depend on the location of the arteriovenous malformation in your body.

If you experience any of these symptoms, do not assume it is due to arteriovenous malformations. These symptoms may be caused by other, less serious health conditions. If you experience any one of them, see your physician.

• Intracranial hemorrhage – bleeding within the skull

• • This is the most common symptom, affecting approximately half of those with arteriovenous malformations.

• Seizure – occurs in 20%–25% of all cases

• Headache

• • Headaches are a common symptom, affecting approximately 15% of cases. Sometimes, headaches linked to one side of the head may be a sign that an arteriovenous malformation is there.

• Muscle weakness

• Paralysis (loss of movement) on one side of the body

• Dizziness

• Inability to perform purposeful movements but not due to paralysis (also known as apraxia)

• Loss of coordination, especially when walking (also known as atraxia)

• Abnormal blood flow sound

• • This sound, also called a bruit, can be identified by your doctor by using a stethoscope. It is caused by the extremely fast flow of blood through arteries and veins of an arteriovenous malformation.

• Sudden, severe back pain

• Difficulty speaking or understanding language

• Loss of sensations (hearing, taste, or touch)

• Visual disturbances

• Memory loss

• Difficulty thinking or mental confusion

• Hallucinations

• Dementia

Children under the age of two may have different symptoms, including:

• Congestive heart failure (inability of the heart to pump out all the blood that returns to it)

• Hydrocephalus (excessive build-up of fluid within the brain—gives the appearance of a large head)

• Seizures

Diagnosis

Your doctor will ask about your symptoms and medical history, and perform a physical exam.

Your doctor will need more information to make an evaluation. To get a more comprehensive understanding of your condition, your doctor may order some tests. Tests may include the following:

• Angiography or Arteriography – Dye (also called a contrast agent) is injected into your arteries and x-rays are taken to determine blood circulation.

• Superselective Angiography – A catheter, which is a very thin, flexible tube, is inserted into your artery until it reaches the site of the arteriovenous malformation. Your physician will then release a small amount of a dye (contrast agent) directly into the lesion. Then x-rays are taken to examine blood flow at the lesion site.

• Computed Axial Tomography (CT Scan or CAT Scan) – A computer takes information from multiple x-rays taken of your head, brain, and/or spinal cord. Often used to determine and locate hemorrhages.

• Magnetic Resonance Imaging (MRI) – Using magnets and radio waves, your doctor obtains images of your brain and spinal cord. MRIs are very sensitive and can show if hemorrhaging has occurred. It can also provide information about the location and physical features of the arteriovenous malformation.

• Magnetic Resonance Angiogram (MRA) – This test involves the injection of a contrast dye into your arteries, after which images are obtained through the use of an MRI machine.

Your doctor will most likely refer you to a specialist for further examination and treatment. There are a number of specialists who focus on arteriovenous malformation, including neurologists, neurosurgeons, and neuroradiologists.

Treatment

The goal of treatment is to prevent hemorrhaging, which can lead to strokes. Your doctor will need to determine if your arteriovenous malformation has bled, if it is not too large, and if it is located in an area that can be easily reached and treated.

Talk with your doctor about the best treatment plan for you. Treatment options include the following:

• Medication – Medication may be taken to ease the symptoms you may be experiencing, such as headache, back pain, and seizures. This, however, does not eliminate the arteriovenous malformation.

• Surgery – You must work with your doctor to decide whether you’d like to go ahead with surgery to treat your arteriovenous malformation or not. Leaving an arteriovenous malformation untreated may lead to serious complications. However, there is always a risk of nervous system damage with surgery.

There are three different types of surgery available and the choice of which one will depend on the size and location of the arteriovenous malformation. The types of surgery include:

• Conventional Surgery – This standard surgery involves doing surgery on the area of the brain or spinal cord where the arteriovenous malformation, including the fistula, is located. This procedure is the most thorough treatment for arteriovenous malformations.

• Endovascular Embolization – Endovascular embolization is often used for arteriovenous malformations that are located deeper within the brain. Regular surgery cannot be used for risk of damage to the surrounding tissue in the brain or spinal cord. A surgeon will guide a catheter through your arteries until it reaches the arteriovenous malformation. Then a substance will be inserted to plug the fistula. This procedure does not destroy the arteriovenous malformation but it does reduce the blood flow to the arteriovenous malformation and make surgery safer.

• Radiosurgery – This procedure uses a beam of highly concentrated radiation focused directly on the arteriovenous malformation. The radiation damages the walls of the blood vessels leading to the arteriovenous malformation. This procedure does not always totally destroy the arteriovenous malformation, especially if it is very large.

Sometimes, arteriovenous malformations are best left alone based on their size and location. It is best to speak with your physician about your decision.

Prevention

There is no way to prevent an arteriovenous malformation. However, to help reduce your chances of hemorrhaging, take the following steps:

• Learn about ways to avoid high blood pressure, such as:

• • Avoid heavy lifting

• • Stop smoking

• • Maintain a healthy weight

• • Drink alcohol only in moderation

• • Eat a healthy diet, with an appropriate but not excessive amount of sodium

• Avoid blood thinners (drugs such as warfarin)

• Continue to see your doctor and a neurologist to regularly check the condition of your arteriovenous malformation

RESOURCES:

American Stroke Association
www.strokeassociation.org

National Institute of Neurological Disorders and Stroke (NINDS)
National Institutes of Health (NIH)
www.ninds.nih.gov/index.htm

CANADIAN RESOURCES:

BC Health Guide
http://www.bchealthguide.org

The Toronto Brain Vascular Malformation Study Group
http://brainavm.uhnres.utoronto.ca

References:

About arteriovenous malformation. Mayo Clinic website. Available at: http://www.mayoclinic.org/arteriovenous-malformation/aboutavm.html. Accessed August 16, 2005.

Arteriovenous malformations and other vascular lesions of the central nervous system fact sheet. National Institute of Neurological Disorders and Stroke website. Available at: http://www.ninds.nih.gov/disorders/avms. Accessed August 16, 2005.

Cerebrovascular Imaging and Intervention Committee of the American Heart Association Cardiovascular Council. What is an arteriovenous malformation (AVM)? American Stroke Association website. Available at: http://www.americanheart.org/downloadable/stroke/1095279678689. Accessed August 16, 2005.

Choi JH, Mohr JP. Brain arteriovenous malformations in adults. Lancet Neurology. 2005; 4(5):299-308.

Ogilvy CS, Stieg PE, Awad I, et al. Recommendations for the management of intracranial arteriovenous malformation: a statement for healthcare professionals from a special writing group of the Stoke Council, American Stroke Association. Stroke. 2001; 32:1458.

Treatment of arteriovenous malformation. Mayo Clinic website. Available at: http://www.mayoclinic.org/arteriovenous-malformation/. Accessed August 16, 2005.