Arteriovenous fistula (AVF) refers to an abnormal connection between an arterial blood vessel and its corresponding venous blood vessel. Normally a high-pressure artery is connected to a network of small blood vessels, capillaries that serve to damp the high pressure and deliver nutrients to tissues and end organs, e.g. the brain. Once blood has passed through capillaries, it passes to the low-pressure, venous system which serves to return blood back to the heart. Where an arteriovenous fistula exists the capillary network has been by-passed and high-pressure arterial blood passes into the low pressure venous system. A dural arteriovenous malformation is located in the dura-mater. Dura-mater is one of the layers that lie between the brain and the skull. These layers act like a balloon and contain the cerebro-spinal fluid that protects the brain from small impacts.
Dura-mater is one of the layers that lie between the brain and the skull.
Location of the dural AVF is one of the key elements to a frequently observed symptom, i.e. “whooshing” or heartbeat noise that can be constantly or intermittently heard, usually in one ear. Classification of dural AVF’s is important because this indicates a patient’s risk of bleeding from the fistula and the consequences that may occur from a bleed.
Under the Borden classification system dural AVF’s are classified into 3 areas:
- Fistula where the venous drainage goes directly into the dural venous sinus or meningeal vein.
- Fistula where the venous drainage goes directly into the dural venous sinus but there is additional cortical venous reflux.
- Fistula where the venous drainage goes directly into the subarachnoid veins.
A class 1 fistula has a low risk of bleeding but can have significant disability. Usual disabilities include frequent severe headaches or continual “whooshing” sound in the ear. Some patients are able to deal with these symptoms but others cannot. Patients who have significant disability can choose to have their fistula treated. Class 2 and 3 fistula’s represent a significant risk to a patient from intracranial bleeding. These fistulas should be treated promptly.
The treatment for dural AVF’s can include embolization, surgery, and in some cases radiosurgery. Embolization is often used as the primary therapy to treat this problem.
It may be possible to treat part or all of the AVF by placing a small catheter inside the blood vessels that supply the AVF and blocking off the abnormal blood vessels with a variety of different materials. These include liquid tissue adhesives (glues), micro-coils, particles, and other materials used to stop blood flowing to the AVF. Endovascular therapy is usually performed prior to surgery or stereotactic radiosurgery.
If there are no symptoms or almost none, or if an AVF is in an area of the brain that cannot be easily treated, conservative medical management may be indicated. If possible, a person with an AVF should avoid any activities that may excessively elevate blood pressure, such as heavy lifting or straining, and they should avoid blood thinners like warfarin. A person with an AVF should have regular checkups with his or her doctor.
If an AVF has bled and/or is in an area that can be easily operated upon, then surgical removal may be recommend. The patient is put to sleep with anesthesia, a portion of the skull is removed, and the AVF is surgically removed. When the AVF is completely taken out, the possibility of any further bleeding should be eliminated.
An AVF that is not too large, but is in an area that is difficult to reach surgery, may be treated by performing stereotactic radiosurgery. In this procedure a cerebral angiogram is done to localize the AVF. Focused-beam, high-energy sources are then concentrated on the dural AVF to produce direct damage to the vessels that will cause a scar and allow the AVF to “clot off.”
Lateral cerebral angiogram imaging showing a dural arteriovenous fistula within the posterior cerebellum
Left: Lateral cerebral angiogram showing a dural arteriovenous fistula within the posterior cerebellum
Right: Lateral cerebral angiogram showing a microcatheter placed within an arterial feeder supplying the dural arteriovenous fistula
Left: Lateral cerebral angiogram showing glue cast within the arterial feeder and the associated dural arteriovenous fistula
Right: Lateral cerebral angiogram, post glue treatment, showing closure of the dural arteriovenous fistula