What is an Arteriovenous Malformation

What is a brain AVM?

Normally, arteries carry blood containing oxygen from the heart to the brain, and veins carry blood with less oxygen away from the brain and back to the heart. When an arteriovenous malformation (AVM) occurs, a tangle of blood vessels in the brain bypasses normal brain tissue and directly diverts blood from the arteries to the veins.

How common are brain AVMs?

Brain AVMs occur in less than 1 % of the population. AVMs are more common in males than in females.

Why do brain AVMs occur?

Brain AVMs are usually congenital, meaning someone is born with one. But they’re usually not hereditary. People probably don’t inherit an AVM from their parents, and they probably won’t pass one on to their children.

Where do brain AVMs occur?

Brain AVMs can occur anywhere within the brain or on its covering.

Do brain AVMs change or grow?

Most AVMs don’t grow or change much, although the vessels involved may dilate (widen).

What are the symptoms of a brain AVM?

Symptoms may vary depending on where the AVM is located:

• More than 50% of patients with an AVM have an intracranial hemorrhage.
• Among AVM patients, 20% to 25% have focal or generalized seizures.
• Patients may have localized pain in the head due to increased blood flow around an AVM.
• 15% may have difficulty with movement, speech and vision.

What causes brain AVMs to bleed?

A brain AVM contains abnormal; therefore, “weakened” blood vessels that direct blood away from normal brain tissue. These abnormal and weak blood vessels dilate over time. Eventually, they may burst from the high pressure of blood flow from the arteries.

What are the chances of a brain AVM bleeding?

The chance of a brain AVM bleeding is 1% to 3% per year.

Does one bleed increase the chance of a second bleed?

The risk of recurrent intracranial bleeding is slightly higher for a short time after the first bleed. People who are between 11 to 35 years old and who have an AVM are at a slightly higher risk of bleeding.

What can happen if a brain AVM causes a bleed?

The risk of death related to each bleed is 10% to 15%. The chance of permanent brain damage is 20% to 30%. Each time blood leaks into the brain, normal brain tissue is damaged. This results in loss of normal function, which may be temporary or permanent.

Are there different types of brain AVMs?

• True arteriovenous malformation (AVM). This is the most common brain vascular malformation. It consists of a tangle of abnormal vessels connecting arteries and veins with no normal intervening brain tissue.
• Occult or cryptic AVM or cavernous malformations. This is a vascular malformation in the brain that doesn’t actively divert large amounts of blood. It may bleed and often produce seizures.
• Venous malformation. This is an abnormality only of the veins.
• Hemangioma. These are abnormal blood vessel structures usually found at the surface of the brain and on the skin or facial structures.
• Dural fistula. The covering of the brain is called the “dura mater.” An abnormal connection between blood vessels that involve only this covering is called a dural fistula. Dural fistulas can occur in any part of the brain covering. Three kinds of dural fistulas are:
  • Dural carotid-cavernous sinus fistula. These occur behind the eye. Patients have eye swelling, decreased vision, redness and congestion of the eye. They often can hear a “swishing” noise.
  • Transverse-Sigmoid sinus dural fistula. These occur behind the ear. Patients usually complain of hearing a continuous noise (bruit) that occurs with each heartbeat, local pain behind the ear, headaches and neck pain.
  • Sagittal sinus and scalp dural fistula. These occur toward the top of the head. Patients complain of noise (bruit), headaches, and pain near the top of the head; they may have prominent blood vessels on the scalp and above the ear.

What is the best treatment for a dural fistula?

The best treatment is usually endovascular surgical blocking of the abnormal connections that have caused the fistula. This involves inserting small tubes (catheters) inside the blood vessel with X-ray guidance and blocking off the abnormal connections.

How are AVMs diagnosed?

Most AVMs are detected with either computed tomography (CT) brain scan or a magnetic resonance imaging (MRI) brain scan. For any type of treatment involving an AVM, an angiogram may be needed to better identify the type of AVM.

What factors influence whether an AVM should be treated?

In general, an AVM may be considered for treatment if it has bled, if it’s in an area of the brain that can be easily treated and if it’s not too large.

What is the best treatment for an AVM?

It depends on what type it is, the symptoms it may be causing and its location and size.

What different types of treatment are available?

• Medical therapy. If there are no symptoms or almost none, or if an AVM is in an area of the brain that can’t be easily treated, conservative management may be called for. These patients are advised to avoid excessive exercise and stay away from *blood thinners like warfarin.
• Surgery. If an AVM has bled and/or is in an area that can be easily accessed, then surgery may be recommended.
• Stereotactic radiosurgery. An AVM that’s not too large but is in an area that’s difficult to reach by regular surgery may be treated with stereotactic radiosurgery. In this procedure, a cerebral angiogram is done to localize the AVM. Focused-beam high energy sources are then concentrated on the AVM to cause a scar and allow the AVM to “clot off.”
• Interventional neuroradiology/endovascular neurosurgery. It may be possible to treat part or all of the AVM by placing a catheter inside the blood vessels and blocking off the abnormal vessels with various materials, such as glue or coils.
  

What doctors specialize in treating brain AVMs?

• Vascular neurosurgeons specialize in surgical removal.
• Radiation therapists/neurosurgeons specialize in stereotactic radiosurgery treatment.
• Interventional neuroradiologists/endovascular neurosurgeons specialize in endovascular therapy.
• Stroke neurologists specialize in the medical management of brain AVMs. Neuroradiologists specialize in the diagnosis and imaging of the head, neck, brain and spinal cord.

(* Some medications are commonly called blood thinners because they can help reduce a blood clot from forming. There are three main types of blood thinners that patients commonly take: anticoagulants like warfarin or heparin, antiplatelet drugs like aspirin, and fibrinolytics like tPA (tissue plasminogen activator). Each type of medication has a specific function to prevent a blood clot from forming or causing a blocked blood vessel, heart attack, or stroke.)