An arteriouvenous fistula (AVF) is an abnormal connection between an artery and a vein.
An AVF can occur anywhere in the body, although they are mostly found in the head, neck, spine and liver.
When there is a fistula in the brain, it is called an arteriovenous malformation (AVM).
With an AVM, the capillaries that normally exchange blood between the arteries and veins—which work together to circulate blood between the heart, lungs and brain— don’t develop or are entangled in a certain area, causing the blood to flow quickly and directly from the arteries into the veins, bypassing the surrounding tissues.
Unlike arteries, veins do not have strong walls, and the blood pressure resulting from direct blood flow can cause the veins to swell, risking rupture, hemorrhage (leaking) and reduced blood flow to the brain.
AVM has no known cause. Most people with AVM are born with the condition, although sometimes it forms later in life.
The onset of symptoms can begin at any age, but most commonly occurs between the ages of 10 and 40. Once someone reaches middle age, AVMs tend to remain stable and are less likely to produce any symptoms.
Similar to an aneurysm, an AVM may not show any signs or symptoms until it ruptures, resulting in bleeding in the brain (hemorrhage). In people without hemorrhage, symptoms can also include:
How is it diagnosed?
Cerebral angiogram. With the help of biplane interventional imaging, a small tube called a catheter is inserted into a major artery (typically, in the groin) and guided through the arteries in the heart up to the brain.
Biplane imaging technology produces detailed 3-D images of the structure and location of blood vessels, soft tissues and blood flow in real-time, enabling providers to identify an AVM and evaluate its condition.
CT scan (computerized tomography). This scan is performed to identify bleeding in the brain, and is often the initial step in diagnosis. The scan uses a series of X-rays to create detailed, 2-D images of the brain.
Contrast dye can be injected into the blood vessels to help highlight blood flow throughout different areas of the brain, better enabling providers to detect any abnormalities, such as an AVM. When dye is used to assist in this type of scan, the variation is called a CT angiogram.
MRI (Magnetic resonance imaging). An MRI renders intricate images of the brain, utilizing powerful magnets and radio waves, rather than radiation, to produce 2-D and 3-D images of the soft tissue.
Compared to a CT scan, MRI technology can show more subtle changes in brain tissue and a more precise location of any malformation and related bleeding, which is helpful in diagnosing an AVM.
What are the treatment options?
The main goal of treating an unruptured AVM is to prevent hemorrhage, and treatments vary according to the patient's age and overall health, as well as the size and location of the AVM.
The three treatment options include surgical removal, endovascular embolization and stereotactic radiosurgery.
Surgical removal (resection) is usually prescribed when the AVM can be removed with little risk of complication; for example, when it’s positioned close to the brain’s surface rather than deep within the brain tissue.
Similar to the clipping method for aneurysms, this method involves opening up the skull and placing small metallic clips being placed along the abnormal blood vessels to separate them from the rest of the brain tissue.
Endovascular embolization is a minimally invasive procedure made possible with the use of biplane interventional imaging. The detailed, 3D images produced by the biplane help the provider guide a catheter through the leg artery and thread it through blood vessels in the brain, eventually positioning it in one of the AVM’s feeding arteries.
Then, an embolizing agent (like a coil) is injected to block off the artery and reduce blood flow to the AVM.
Another option, stereotactic radiosurgery (SRS) uses many precisely focused radiation beams to destroy the AVM, rather than open surgery.