Pulmonary arteriovenous malformations (AVMs) are the abnormal connections between a pulmonary artery and a pulmonary vein. Most cases are congenital, and although uncommon, they are a significant part of the differential diagnosis of pulmonary problems like hypoxemia and lung nodules. These abnormal communications between pulmonary arteries and pulmonary veins usually bypass the capillary bed and lead to right-to-left shunting of blood, which in turn can lead to symptoms depending on the degree of blood shunting. Pulmonary AVMs are also known by other terms such as pulmonary arteriovenous fistulas, pulmonary arterio-venous aneurysms, cavernous hemangiomas, and pulmonary angiomas. In 1897 during an autopsy study, this malformation was recorded for the first time in literature by Churton.
Most patients with pulmonary AVMs have the autosomal dominant disease hereditary hemorrhagic telangiectasia (HHT). However, about 15% of patients with pulmonary AVMs do not meet the criteria for the diagnosis of HHT and do not have any other systemic disease. Pulmonary AVMs may also be acquired and found in patients with liver cirrhosis. In these patients, the absence of hepatic 'factor' may lead to the formation of pulmonary AVMs. Pulmonary AVMs may also be acquired secondary to schistosomiasis, tuberculosis, and metastatic thyroid cancer.
Hereditary hemorrhagic telangiectasia (HHT) is an autosomal dominant disorder. The clinical features are secondary to vascular malformations in various organs of the body, most commonly the skin, nasopharynx, GI tract, lungs, and brain. HHT is recognized as a triad of cutaneous telangiectasia, a family history of the disorder, and recurrent epistaxis.
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