An arteriovenous fistula is an abnormal channel or passage between an artery and a vein.
An arteriovenous fistula is a disruption of the normal blood flow pattern. Normally, oxygenated blood flows to the tissue through arteries and capillaries. Following the release of oxygen in the tissues, the blood returns in veins to the heart. An arteriovenous fistula is an abnormal connection of an artery and a vein. The blood bypasses the capillaries and tissues and returns to the heart. Arterial blood has a higher blood pressure than blood in veins. Although both the artery and the vein retain their normal connections, the new opening between the two causes some arterial blood to shunt (be diverted) into the vein because of the blood pressure difference. As a result, the vein swells.
Congenital arteriovenous fistula is rare. Acquired arteriovenous fistula is also uncommon in children. When it occurs, it is most likely to be found in the arms or legs.
Causes and symptoms
There are two types of arteriovenous fistulas, congenital and acquired. A congenital arteriovenous fistula is a rare birth defect that formed during fetal development. In congenital fistulas, blood vessels of the lower extremity are more frequently involved than other areas of the body. An acquired arteriovenous fistula is one that develops after a person is born. It usually occurs when an artery and vein that are side-by-side are damaged, and the healing process results in the two becoming linked. For example, after catheterizations, arteriovenous fistulas may occur as a complication of the arterial puncture in the leg or arm. Fistulas also form without obvious cause. In the case of patients on hemodialysis, physicians perform surgery to create a fistula. These patients receive many needle sticks to flush their blood through dialysis machines and for routine blood analysis testing. The veins used may scar and become difficult to access. Surgery is used to connect an artery and vein so that arterial blood pressure and flow rate widens the vein and decreases the chance of blood clots forming inside the vein.
The main symptoms of arteriovenous fistulas near the surface of the skin are bulging and discolored veins. In some cases, the bulging veins can be mistaken for varicose veins. Other fistulas can cause more serious problems without obvious symptoms, depending on their location and the blood vessels involved.
When to call the doctor
If the child has veins that appear to be varicose, the doctor should be consulted.
Using a stethoscope, a physician can detect the sound of a pulse in the affected vein (bruit). The sound is a distinctive to-and-fro sound. Dye injected into the blood vessels can be tracked by x ray to confirm the presence of a fistula.
Small arteriovenous fistulas can be corrected by surgery. Fistulas in the brain or eye are very difficult to treat. If surgery is not possible or is very difficult, injection therapy may be used. Injection therapy, also called sclerotherapy, is the injection of an irritating chemical that causes scaring at the site of the injection. In the case of an arteriovenous fistula, this procedure should stop the passage of blood from the artery to the vein. Surgery is the most common method of treating acquired fistulas.
The prognosis for treated acquired arteriovenous fistula is usually very good. Congenital arteriovenous fistula is not usually treated quite as successfully, but it can also be treated in such a way as to minimize further problems.
As of 2004, there is no known way to prevent arteriovenous fistula.
If not treated, arteriovenous fistulas can be very dangerous. Tissues below the fistula may not get enough blood and may die. If too much blood is diverted through the fistula, heart complications may occur.
Congenital —Present at birth.
Sclerotherapy —Injection of an irritating chemical into a blood vessel so that it forms a scar to repair itself.
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