Pulmonary Arteriovenous Fistula

What is a Pulmonary Arteriovenous Fistula?

A pulmonary arteriovenous fistula is an abnormal blood vessel that creates a potentially troublesome connection between a vein and an artery in the lung. It acts as a detour, sidestepping the normal route the blood is supposed to take. If a patient has symptoms or problems, medical attention is essential.

Pulmonary arteriovenous fistulas are congenital malformations—that is, they’re present at birth. They appear slightly more often in females than in males. People with hereditary hemorrhagic telangiectasis (HHT) sometimes have these fistulas in different parts of the body, including the lungs. Pulmonary arteriovenous fistulas more commonly appear on their own, independent of an underlying disease.

The Mechanics of Pulmonary Arteriovenous Fistulas

Pulmonary arteriovenous fistulas develop as the child develops in the womb. These abnormal vessels carry blood out of the lung before it is oxygenated—that is, replenished with oxygen. The process is called a “right-to-left shunting” of blood. The outlook is less favorable for patients with HHT than for patients not suffering from it.

In many cases there are no symptoms. In more serious cases, this circumstance can starve the body of oxygen and lead to a variety of complications. In addition, left untreated, these fistulas might lead to a “paradoxical embolism”—a blood clot that travels from the lungs to the arms, legs or brain.

Symptoms of Pulmonary Arteriovenous Fistulas

The most common symptoms are difficulty breathing and blood in the patient’s sputum. But symptoms also can include:

• Fingers and toes turning bluish
• Fingers and toes becoming puffy or enlarged (clubbing)
• A “murmur” in the lung· Nosebleeds in HHT patients

Causes of Pulmonary Arteriovenous Fistulas

Pulmonary arteriovenous fistulas occur in about one third of all patients with HHT. But the majority of cases are present at birth. Doctors do not know what causes them, and there is no known way to prevent them.

Diagnosing Pulmonary Arteriovenous Fistulas

A diagnosis usually begins with the patient “presenting” one or more of the symptoms. The doctor will run tests to see if the oxygen level in the blood is abnormally low, or if the red cell count in the blood is abnormally high.

In addition the common symptoms, if there is evidence of these blood conditions, the following tests probably will be performed:

• Listening for a murmur in the lungs with a stethoscope
• A chest x-ray to locate the fistula
• A CT (computed tomography) scan to gather details about the fistula’s structure and condition
• A pulmonary arteriogram—a video of dye moving through the blood vessels to map the fistula

Treating Pulmonary Arteriovenous Fistulas

Small pulmonary arteriovenous fistulas might require no treatment at all. In most cases, however, these fistulas need to be corrected. There are two treatments used:

• Surgery to remove the abnormal blood vessel and nearby lung tissue
• Embolization (at the time of the arteriogram) to block the fistula and the flow of blood

Surgery is almost always successful. With embolization, however, the problem can recur if the blockage gives way or is overcome. For that reason, patients usually are screened for “favorable anatomy” before a decision is made to perform an embolization.

Oxygen is Job 1
Of all the illnesses that can affect the lungs, a pulmonary arteriovenous fistula might reveal their key function best. The lungs act as “transfer stations,” delivering much-needed oxygen to the blood as it passes through them. Interrupt or sidestep these deliveries and things break down. The good news: These deliveries can be restored relatively easily with removal or repair of the fistula.