Dural Arteriovenous Fistula
An arteriovenous fistula (AVF) is a short-circuit connection between an artery and a vein. This bypasses the normal flow of blood through capillary vessels. In a dural AVF, the artery is in the thick membrane (dura) which covers the brain. This artery may connect directly to a large vein channel in the dura (called a dural sinus) or a vein on the surface of the brain.
The dural AVF shunts blood under higher pressure in a dural artery into the lower pressure venous side. This increases pressure and blood flow in the vein or dural sinus. The pressure can become high enough to prevent blood from draining away from the brain. This is called venous hypertension. It may also reverse the normal direction of blood flow in the vein on a brain surface. This is termed retrograde cortical venous drainage.
Symptoms can be mild initially, but often may progress. With retrograde cortical venous drainage, there is risk for hemorrhage.
A dural AVF may also occur in the spine. It usually develops in older men. The most common symptom is a problem with spinal cord function resulting from venous hypertension.
Signs and Symptoms
Some dural AVFs do not cause symptoms. When present, symptoms may include:
- Constant humming or “whooshing” in an ear which corresponds to your heartbeat (pulsatile tinnitus)
- Redness, bogginess and slight prominence of your eye
- Trouble with vision
- Stroke-like symptoms or hemorrhage
Dural AVFs can occur after trauma, but many times they happen for no known reason. Some may develop as a result of blood clotting in a dural sinus.
Diagnosis of a dural AVF starts with a medical history and neurological exam. A stethoscope placed over the area of the fistula may reveal a bruit, an abnormal, murmur-like sound due to the altered blood flow. Other diagnostic tests include: angiography , magnetic resonance imaging ( MRI ) or CT scan . CT or MR angiography ( CTA or MRA ) may raise suspicion for a dural AVF, but often are not definitive tests.
If you have a dural AVF, there are several options that may be recommended.
- Observation This is recommended when (1) there does not appear to be high pressure and reversed blood in the veins over the brain surface, (2) symptoms such as pulsatile tinnitus are tolerable. Occasionally, manual pressure over the artery supply to the fistula is considered as a way to possibly treat it.
- Stereotactic Radiosurgery This can be an effective form of treatment, but it may take several years to eliminate the fistula. Generally, it is not recommended for a dural AVF that has retrograde cortical venous drainage (reversed blood flow in a vein on the brain surface) since it may not quickly eliminate the risk for hemorrhage.
- Embolization Through a catheter (small tube) directed to the area of the fistula, special materials are injected to close down the fistula from inside the blood vessels. Under certain circumstances, it can be an alternative to open surgery. However, there is some chance that the dural AVF can recur or return.
- Surgery A small craniotomy is performed to disconnect the fistula. The hair is parted and an incision is made based on the location of the fistula. A window made in the bone is replaced at the end of surgery. The fistula is usually on the surface of the brain, so brain tissue is rarely disturbed. Using an operative microscope, the fistula is simply divided or closed with a special, miniature clip. Typically, an angiogram is done during surgery to make sure that the fistula is completely gone. With successful surgical treatment, there is almost no chance that the dural AVF will come back.