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 ☞Hereditary Telangiectasia), less commonly acquired (hepatic cirrhosis, mitral stenosis, trauma, actinomycosis, Fanconi Syndrome).
Pulmonary Arteriovenous Fistula; PAVM; Osler-Rendu-Weber Syndrome; Osler’s disease.
First described in 1896 by French physician, 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, English Dermatologist, Frederick Parkes Weber, described the other manifestations.
Estimated to occur in less than 1:5,000. Approximately 10% of the cases are identified during infancy and childhood, with a gradual increase through the fifth and sixth decades. Fewer than 50 cases have been described in neonates.
Unknown. Male predominance during the neonatal period, but female preponderance (2:1) in adults.
The exact pathogenesis remains 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 ...