Dural Arteriovenous Fistula
What Is It?
A dural arteriovenous fistula, or dural arteriovenous malformation, is an abnormal connection (fistula) between arteries in the dural covering of the brain and spinal cord with veins or venous sinuses.
Normally, arteries carry blood to tissues where they divide into smaller and smaller capillaries before returning to veins and venous sinuses which collect blood and direct it back to the heart. In these lesions there is no capillary bed and the arteries connect directly to the veins or venous sinuses. Venous sinuses are large channels of venous blood that occur around the brain and normally collect the venous blood which comes from the brain. In the case of the dural arteriovenous fistula, the arteries in question are called meningeal arteries because they normally feed the meninges, or the coverings of the brain and spinal cord. The dura is the outermost and thickest covering layer of the meninges.
This abnormal connection of an artery and a vein leads to high blood flow through the fistula which produces abnormally high pressures in the vein or sinus which can lead to the clinical manifestations discussed below. These fistulas vary in their size, location and the type of venous channel that they drain into.
It is not known what causes an arteriovenous fistula. They are rare pathology, occurring in less than 1 in a million people.
What Types of Symptoms Are Typical?
The presenting symptoms of a fistula vary from patient to patient depending on the location, size and type of the lesion. Some possible symptoms include:
- Bruit (pronounced "brew-ee"): This is an abnormal noise in the head, often described as wooshing sound.
- Pulsatile tinnitus: Tinnitus is a ringing in the ears. In this case it is pulsatile, getting louder with each heartbeat.
- Swelling or redness of the eye: In some fistulae the increased venous pressure can lead to this symptom, particularly with ones that drain into the cavernous sinus.
- Stroke-like symptoms: The back up of blood in the venous circulation can compromise normal flow of blood from the brain, leading to neurological symptoms similar to stroke. This varies considerably depending on the location and areas of the brain that are involved.
Additionally, some dural arteriovenous fistulas can be asymptomatic.
In some patients with very high venous pressures due to the fistula, the dilated veins or venous sinuses (called a varix or varices) can rupture and bleed causing a hemorrhage around the brain and leading to acute deterioration in neurological function. Symptoms may occur suddenly and can include nausea and vomiting and a decreased level of consciousness.
How Is The Diagnosis Typically Made?
After a neurological assessment
which is suggestive of a dural arteriovenous malformation, some neurological imaging study, such as CT scan
or MRI scan
, is generally ordered. While these studies can sometimes reveal evidence of a fistula, the definitive diagnosis must be made on a cerebral angiogram
. This study allows visualization of the blood vessels in the head and can directly reveal the abnormal connection between the artery and vein. This study both diagnoses the fistula and gives information about its size, location and type. Furthermore, some treatment options can be performed through the angiography catheter.
What Are Some Common Treatments?
Treatment for arteriovenous fistula varies depending on the specifics of each case. Some patients who are asymptomatic or have very minor fistulae without significant venous pressure may opt to simply follow it without treatment.
However, patients who have any significant symptoms, bleeding, neurological dysfunction or concerning signs such as very high venous pressure will opt to have treatment. Treatment varies depending on the type and location of the fistula. Generally there are two options which may be used alone or in combination. Some fistulae can be embolized, or blocked, through endovascular techniques. At the time of an angiogram, the catheter is maneuvered into the arteries feeding the fistula. They are then blocked off by some embolization material, usually a special glue which fills the blood vessel. Alternatively, surgery to clip or separate the abnormal connection can be performed in some cases. If the fistula can be completely occluded by one of these methods the fistula is generally considered cured and rarely recur.
Patients who present with significant hemorrhage may require a surgery to evacuate the blood.
As each patient's case is different, the discussion of treatment and prognosis for arteriovenous fistula should be made between each patient and their treating physicians.
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This site is not intended to offer medical advice. Every patient is different, and only your personal physician can help to counsel you about what is best for your situation. What we offer is general reference information about various disorders and treatments for your education.