Arteriovenous fistula

[Luis Fok]

An arteriovenous fistula is an abnormal channel between an artery and a vein.

Rarely, a large fistula may divert enough blood to cause symptoms of reduced blood flow in the affected arm or leg (steal syndrome).
Although doctors may be able to hear the distinctive sound of blood flow though a fistula by using a stethoscope, imaging tests are often needed.
Fistulas can be cut out or eliminated with laser therapy, or sometimes substances are injected into the fistula to block the blood flow.

(See also Overview of the Venous System.)
Normally, blood flows from arteries into capillaries and then into veins. When an arteriovenous fistula is present, blood flows directly from an artery into a vein, bypassing the capillaries. Arteriovenous fistulas may be

Congenital, meaning the person was born with one
Acquired, meaning that it developed after birth

Congenital arteriovenous fistulas are uncommon.
Acquired arteriovenous fistulas can be caused by any injury that damages an artery and a vein that lie side by side. Typically, the injury is a piercing wound, as from a knife or bullet. The fistula may appear immediately or may develop after a few hours. The area can swell quickly if blood escapes into the surrounding tissues.