Pulmonary Arteriovenous Malformation

Pulmonary Arteriovenous Malformation (PAVM) is a direct communication between branches of the pulmonary arterial and venous vessels representing right-to-left shunting and therefore not participating in pulmonary gas exchange. Usually congenital (70% are associated with Osler-Rendu-Weber Disease), less commonly acquired (hepatic cirrhosis, mitral stenosis, trauma, actinomycosis, Fanconi Syndrome).

Pulmonary Arteriovenous Fistula; PAVM; Rendu-Osler-Weber Syndrome; Osler's disease.

First described in 1896 by Henry Jules Rendu after his description of telangiectasia and epistaxis. Sir William Osler reported a family known to have hereditary hemorrhagic telangiectasia in 1897. In 1907, Federick Weber described the other manifestations.

Unknown, but very rare. Approximately 10% of the cases are identified during infancy and childhood, with a gradual increase through the fifth and sixth decades. Only about 20 cases have been described in neonates. Frequency in United States, 1:39,216 persons. In some regions of France, 1:2351 persons has been reported.

Unknown. Male predominance during the neonatal period, but female preponderance (2:1) in adults.

The exact pathogenesis of PAVM still unknown. Pulmonary lesions function as right-to-left shunts and may cause hypoxemia or paradoxical embolization. Histologically, there is endothelial and smooth-muscle cell degeneration, defects in the endothelial junctions, and weakness of the perivascular connective tissue. Weakness of the vessel walls may predispose to hemorrhage despite normal coagulation and platelet functions. Autopsy results show that 75% of patients had unilateral disease, 35% had multiple lesions, and about half of the latter had bilateral lesions. The PAVM can be classified as simple (those with a single feeding segmental artery and a single draining vein) and complex (two or more feeding arteries or veins). The pulmonary artery pressure is normal or low in nearly all patients with PAVM.

The diagnosis is usually suspected from the clinical history. The classical radiological sign on a chest radiograph is that of a round or oval mass of uniform density, frequently lobulated, but sharply defined, found most often in the lower lobes. Shunt fraction measurement in 100% oxygen is a sensitive and reasonably specific diagnostic test for PAVM. The presence of a PAVM can be further evaluated via contrast echocardiography, radionuclide perfusion lung scan, 3D helical CT scan, or MRI. However, pulmonary angiography remains the standard criterion in the diagnosis of PAVM.

Symptoms vary from being totally asymptomatic to severe with presentation in childhood with cyanosis and shortness of breath on exertion, congestive heart failure, or respiratory failure. Murmurs or bruits over the site of the PAVM may be present in half the patients and louder during inspiration. Increased FiO2 (fraction of inspired oxygen) may not significantly improve oxygenation. Secondary polycythemia is present and the degree depends on the severity of cyanosis. The condition is associated with hereditary hemorrhagic telangiectasia (Rendu-Osler-Weber syndrome) in 60 to 70% of patients; conversely, 15 to 30% of patients with hereditary hemorrhagic telangiectasia have PAVM. Hemoptysis from rupture of the lesions may occur. Thrombosis may occur within the fistula with systemic embolization leading to neurological complications (transient ischemic attacks, hemiplegia, brain abscesses, or seizures) in about one-third of the patients. Hemothorax and/or hemoptysis are often lethal complications of arteriovenous fistulae. Because mortality is high in symptomatic patients, surgical resection of the involved lung segment is often performed. However, embolotherapy based on occlusion of the feeding arteries of the PAVM is currently the treatment of choice.

Evaluate the site and involvement of the pulmonary arteriovenous fistula, including chest radiograph, CT scan, and/or MRI of the thorax. Pulmonary angiography enables visualization of the lesions and guides surgical or radiological management. Exclude concomitant cerebral arteriovenous malformation or abscess by neuroimaging studies. Check cardiac function and look for signs of high-output congestive heart failure, because a big PAVM may lead to increased cardiac output. Laboratory investigations should include a CBC and arterial blood gas analysis.

Systemic desaturation from intrapulmonary shunt is little influenced by supplemental oxygen therapy. Cardiac output should be maintained to avoid further desaturation. Nasal intubation and insertion of a nasogastric tube carry a high risk of bleeding in hereditary hemorrhagic telangiectasia patients and should be avoided. Maneuvers that reduce blood flow through the fistula improve oxygenation (fistula in nondependent position, avoidance of positive end-expiratory pressure, lowering of pulmonary vascular resistance). Venous lines should be meticulously checked and cleared from air bubbles to prevent systemic embolization. Polycythemia may result in neurologic deficits and should be controlled perioperatively. Tracheal intubation should be performed with care to prevent bleeding from telangiectatic airway lesions. Blood loss may be considerable during resection of the PAVM; therefore large-bore intravenous access and replacement blood should be available. Lung separation via a double-lumen tube or bronchial blocker should be used to protect the dependent lung from possible endobronchial bleeding.

There are no known pharmacological implications.

Hereditary Telangiectasia: Autosomal dominant transmitted mucocutaneous and visceral fibrovascular dysplasia with telangiectasia, arteriovenous malformations, and aneurysms, often widely distributed throughout the cardiovascular system. It is usually recognized as a “triad” of telangiectasia, recurrent epistaxis, and a family history of the disorder.