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Brain AVM (arteriovenous malformation)
By Mayo Clinic staffMayo Clinic Health Manager
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Definition
A brain AVM (arteriovenous malformation) is an abnormal connection between arteries and veins that interrupts the normal flow of blood between them. An AVM, which is present at birth (congenital), can develop anywhere in your body but occurs most often in the brain or spine. A brain AVM, which appears as tangles of normal and dilated blood vessels, can occur in any part of your brain. The cause isn't clear.
You may not know you have a brain AVM until you experience symptoms, such as headaches or a seizure. In serious cases, the blood vessels rupture, causing bleeding in the brain (hemorrhage). Once diagnosed, a brain AVM can often be treated successfully.
Symptoms
A brain AVM (arteriovenous malformation) often causes no signs or symptoms until the AVM ruptures, resulting in bleeding in the brain (hemorrhage).
Signs and symptoms of a brain AVM include:
- Seizures
- A whooshing sound (bruit) that can be heard on examination of the skull with a stethoscope
- Pulsing noise in the head (pulsatile tinnitus)
- Headache
- Progressive weakness or numbness
When bleeding into the brain occurs, signs and symptoms can be similar to a stroke and may include:
- Sudden, severe headache
- Weakness or numbness
- Vision loss
- Difficulty speaking
- Inability to understand others
- Severe unsteadiness
A bleeding brain AVM is life-threatening and requires emergency medical attention.
Symptoms may begin at any age, but you're more likely to experience symptoms before age 50. Brain AVM can damage brain tissue over time. The effects slowly build up, sometimes causing symptoms in early adulthood. Once you reach middle age, however, brain AVMs tend to remain stable and are less likely to cause symptoms.
For women, pregnancy may start or worsen symptoms because of the increased blood flow and blood volume during pregnancy.
When to see a doctor
If you notice any signs or symptoms of a brain AVM, get medical help right away.
Causes
A brain AVM is an abnormal connection between arteries and veins in your brain. Doctors believe that a brain AVM develops during fetal development. Why this occurs for some babies and not others is unknown.
Normally, your heart sends oxygen-rich blood to your brain through arteries, which branch into smaller arterioles and subsequently to capillaries, the smallest blood vessels. Oxygen is removed from blood in the capillaries and used by your brain. The oxygen-depleted blood then passes into small venules and then into larger veins that drain the blood from your brain, returning it to your heart and lungs to get more oxygen.
If you have a brain AVM, blood passes directly from your arteries to your veins via abnormal vessels. This disrupts the normal process of how blood circulates through your brain.
Risk factors
Anyone can be born with a brain AVM, but AVMs are more common in boys than in girls.
Symptoms of AVM are more likely to occur before age 50. Brain AVM can damage brain tissue over time. The effects slowly build up, sometimes causing symptoms in early adulthood. Once you reach middle age, however, brain AVMs tend to remain stable and are less likely to cause symptoms.
For women, pregnancy may start or worsen symptoms because of the increased blood flow and blood volume during pregnancy.
Complications
Complications of a brain AVM include:
- Bleeding in the brain (hemorrhage). Walls of the affected arteries and veins may become thin or weak. An AVM puts extreme pressure on these walls, since no capillaries are available to slow down the blood flow. A hemorrhage may result. A very small (microscopic) hemorrhage causes limited damage to surrounding tissues and is unlikely to produce noticeable symptoms. A larger hemorrhage, however, can cause a hemorrhagic stroke and brain damage.
- Reduced oxygen to brain tissue. With an AVM, blood bypasses the network of capillaries and flows directly from arteries to veins. Blood rushes quickly through the altered path since it isn't slowed down by channels of smaller blood vessels. Surrounding brain tissues can't easily absorb oxygen from the fast-flowing blood. Without enough oxygen, brain tissues weaken or may die off completely. This results in stroke-like symptoms, such as difficulty speaking or severe unsteadiness.
- Thin or weak blood vessels. An AVM puts extreme pressure on the thin and weak walls of the blood vessels. A bulge in a blood vessel wall (aneurysm) may develop and become susceptible to rupture.
- Brain damage. As you grow, more arteries may be "recruited" to supply blood to the fast-flowing AVM. As a result, some AVMs enlarge, which moves or compresses portions of the brain. This may prevent protective fluids from flowing freely around the hemispheres of the brain. If fluid builds up, it can push brain tissue up against the skull — a condition known as hydrocephalus.
Preparing for your appointment
A brain AVM is usually diagnosed in an emergency situation. But in some cases, a brain AVM is found incidentally while diagnosing or treating an unrelated medical condition. You may then be referred to a doctor who specializes in conditions of the brain and nervous system (neurologist).
Because appointments can be brief and there's often a lot of ground to cover, it can help to be well prepared. Here are some tips to help you get ready for your appointment.
What you can do
- Be aware of any pre-appointment restrictions. At the time you make the appointment, be sure to ask if there's anything you need to do in advance.
- Write down any symptoms you're experiencing, including any that may seem unrelated to the reason for which you scheduled the appointment.
- Make a list of all medications, including vitamins, herbs and over-the-counter drugs, that you're taking. Even better, take the original bottles and a written list of the dosages and directions.
- Take along a family member or friend. It can be difficult to absorb all the information provided to you during an appointment. The person who accompanies you may remember something that you forgot or missed.
- Write down questions to ask your doctor. Don't be afraid to ask questions or to speak up when you don't understand something your doctor says.
List your questions from most important to least important in case your time with your doctor runs out. For brain AVM, some basic questions to ask your doctor include:
- What are other possible causes for my symptoms?
- What tests are needed to confirm the diagnosis?
- What are my treatment options and the pros and cons for each?
- What results can I expect?
- What kind of follow-up should I expect?
In addition to the questions that you've prepared to ask your doctor, don't hesitate to ask questions during your appointment at any time that you don't understand something.
What to expect from your doctor
The neurologist is likely to ask about your symptoms, if any, conduct a medical exam and schedule tests to confirm the diagnosis. The tests gather information about the size and location of the AVM to help direct your treatment options. Your doctor will talk to you throughout the process and tell you what tests are being performed and why.
Tests and diagnosis
Diagnosing a brain AVM usually begins with a thorough medical exam by a doctor who specializes in conditions of the brain and nervous system (neurologist). Depending on those results, the doctor may request one or more tests. Imaging tests are usually conducted by radiologists who specialize in imaging the brain and nervous system.
Three main tests are used to diagnose brain AVMs:
- CT scan and CTA. A computerized tomography (CT) scan takes pictures of the brain using X-rays. Sometimes dye is injected through an intravenous tube in a vein so that the arteries feeding the AVM and the veins draining the AVM can be viewed in greater detail. This is called a computerized tomography angiogram (CTA).
- MRI and MRA. Magnetic resonance imaging (MRI), more sensitive than CT in showing AVM, creates images using a large magnet and radio waves. MRI also provides information about the exact location of the malformation, which is very important for determining treatment options. Dye can also be injected to better see the blood circulation in the brain. This is called a magnetic resonance angiogram (MRA).
- Cerebral arteriography. Cerebral arteriography (also known as cerebral angiography) is the most detailed test and the best way to diagnose an AVM. The test reveals the location and characteristics of the feeding arteries and draining veins. A thin tube is inserted into an artery in the groin. This tube is threaded up toward the brain to the blood vessels. Dye is injected into the blood vessels of the brain and X-rays are taken.
Treatments and drugs
Treatment options for brain AVM involve a number of procedures and depend on the size and location of the abnormal blood vessels. Medications may also be used to treat related symptoms, such as headaches or seizures.
Surgical removal (resection)
Surgical treatment of a small brain AVM is relatively safe and effective. A section of skull is removed temporarily to gain access to the AVM. The neurosurgeon, aided by a high-powered microscope, seals off the AVM with special clips and carefully removes it from surrounding brain tissue. Sometimes this is done with a laser. The skull bone is then reattached, and the scalp is closed with stitches.
Resection is usually done when the AVM can be removed with acceptable risk to prevent hemorrhage or seizures. AVMs that are in deep brain regions carry a higher risk of complications. In these cases, other treatments are considered.
Endovascular embolization
During this procedure, a long, thin tube called a catheter is inserted into a leg artery and threaded through the body to the brain arteries. The catheter is positioned in one of the feeding arteries to the AVM, and small particles of a glue-like substance are injected to block the vessel and reduce blood flow into the AVM.
Endovascular embolization may be done alone, before other treatments to reduce the size of the AVM, or during surgery to reduce the chance of bleeding during the operation. In some large brain AVMs, endovascular embolization may reduce stroke-like symptoms by redirecting blood back to normal brain tissue.
Stereotactic radiosurgery
This treatment uses precisely focused radiation to destroy the AVM. The radiation causes the AVM vessels to slowly clot off in the months or years following the treatment. This treatment works best for small AVMs and for those that have not caused a life-threatening hemorrhage.
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- Arteriovenous malformations and other vascular lesions of the central nervous system fact sheet. National Institute of Neurological Disorders and Stroke. http://www.ninds.nih.gov/disorders/avms/detail_avms.htm. Accessed Dec. 11, 2008.
- Higashida RT. What is an arteriovenous malformation (AVM)? American Stroke Association. http://www.americanheart.org/downloadable/stroke/1095279678689What_Is_an_Arteriovenous_Malformation_Final%20Science%20review%206-03-03%20vF3.pdf. Accessed Dec. 11, 2008.
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