About Arteriovenous Malformations (AVMs) and Dural Arteriovenous Fistulae (DAVF)
AVMs are congenital, but may not cause symptoms until later in life, if ever.
Arteriovenous malformations (AVMs) and dural arteriovenous malformations (DAVFs) are abnormalities of blood vessels that cause an abnormal connection between arteries and veins.
Normal Blood Flow
Usually, arteries and veins are connected through a system of tiny blood vessels called capillaries. As blood flows from arteries into capillaries, the blood pressure is lessened. While in capillaries, the blood gives up oxygen and picks up waste products. Then the blood flows from the capillaries into veins.
Abnormal Blood Flow in an AVM or DAVF
With an AVM or DAVF, one or more large arteries connect directly to one or more veins. This abnormal connection of arteries to veins is called a “nidus” or “fistula.” The blood pressure isn’t reduced by capillaries and puts more strain on the blood vessels. An artery, vein, or nidus in an AVM or DAVF can rupture, causing a hemorrhage.
There are certain characteristics of an AMV or DAVF that may predict the risk of hemorrhage. These characteristics can often be checked by an imaging exam such as an MRI. Typically, a cerebral angiogram will be required to accurately assess them and plan treatment.
An AVM can occur anywhere in the body, but the majority is found in the brain and spine. AVMs are usually congenital, meaning people are born with them. They may or may not cause symptoms.
Hemorrhaging in the brain from an AVM may result in a stroke. While the risk of rupture is low, it increases over time (the average risk is 2-4% per year). Consequently, treatment of AVMs in otherwise healthy people is recommended.
Dural Arteriovenous Fistulae (DAVF) are a form of malformation where the fistula happens in the protective covering of the brain or spinal cord (called the dura). Unlike AVMs, DAVFs occur because of a trauma, possibly a head injury, infection, blocked dural sinuses, or surgery.
Reducing the Risk
AVM: There is nothing you can do to prevent an arteriovenous malformation. However, by recognizing symptoms and getting prompt medical attention, you may reduce the risk of having a stroke or spinal damage.
DAVF: While there is nothing that can be done to prevent a DAVF, patients who have had surgery, injury, infection (with the brain or spine) or dural sinus thrombosis should be monitored.
Symptoms of AVMs and DAVFs
Arteriovenous malformations are a serious condition. They can cause a stroke or severe damage to the spinal tissue. Symptoms of an arteriovenous malformation or dural arteriovenous fistula vary. Some people may experience few or no symptoms. Others may have some of the following symptoms:
- Weakness or paralysis in part of the body
- Numbness or tingling
- Vision problems
- Memory problems
- Speech problems
- Loss of coordination
- Hearing a whooshing noise
Diagnosing AVMs and DAVF
Your doctor may order a CT angiography or MR angiography to screen for an arteriovenous malformation or dural fistula. These exams produce detailed images of the blood vessels in the brain and spine and allow a radiologist to accurately identify abnormalities. Due to the nature of these examinations, a physician will usually meet with you in advance to provide a detailed explanation of the procedures involved with diagnosing and treating these conditions.
Treating these Conditions
Endovascular embolization is a minimally invasive procedure for treating arteriovenous malformations and dural fistulae. This procedure uses various substances to block the blood vessels involved in the abnormality. It may be successful on its own, or may be combined with surgery.
The extent of treatment is usually judged by the complexity of the AMV. Treatment is often “staged” if more than one treatment session is expected. Many AVMs will require some combination of therapies, including radiation therapy, endovascular embolization, and surgical removal. Embolization may reduce the overall size of the AVM or DAVF to make surgical removal easier or to increase the effectiveness of radiation. These conditions can occasionally be cured with embolization alone. Newer liquid embolic agents (e.g. Onyx) are increasing this cure rate.