Definition of Pulmonary arteriovenous fistula:

Pulmonary arteriovenous fistula is a condition in which an abnormal connection (fistula) develops between an artery and vein in the lungs. As a result, blood passes through the lungs without receiving enough oxygen.

Causes, incidence, and risk factors:

Pulmonary arteriovenous fistulas are usually the result of a genetic disease that causes the blood vessels of the lung to develop abnormally. Fistulas also can be a complication of liver disease.

Patients with Rendu-Osler-Weber disease (ROWD) -- also called hereditary hemorrhagic telangiectasis (HHT) -- often have abnormal blood vessels in many parts of the body. These abnormal vessels can be in the lungs, brain, nasal passages, liver, and gastrointestinal organs. This condition is slightly more common in women than in men.