PAVMs are defined as abnormal communications between pulmonary arteries and veins without intervening capillary bed. Its prevalence is approximately 1 in 2630 in population scanned by chest CT with a slight predilection for female [1, 3]. PAVMs can be sporadic, multiple or even diffuse lesions as well as uni- or bi-lateral involved. PAVMs often have lower lobe predominance. Histopathologically, PAVMs manifest as tortuous or direct aneurysmal connection developing between arteries and veins without intervening capillary bed, which led to the loss of “filter capacity”.
The etiology of PAVMs could be congenital or acquired. The majority of PAVMs are associated with autosomal dominant disorder called hereditary hemorrhagic telangiectasia (Osler-Weber-Rendu syndrome) . Acquired PAVMs are usually secondary to liver cirrhosis, infections, metastatic carcinomas, chest trauma and iatrogenic procedures . Patients with PAVMs are usually asymptomatic, especially in children. The common pulmonary symptoms include cyanosis of oral mucosa and extremities, digital clubbing, hemoptysis and chest pain. Extrapulmonary manifestations are polycythemia, cerebral abscess, stroke or transient ischemic attack, epistaxis and so on . In our patient, the hypoxemia as well as polycythemia were consequences of right-to-left shunt caused by PAVMs and were responsible for further presentations like digital clubbing and cyanosis.
In our case, the patient was initially treated as polycythemia vera. There might be several reasons why the other clinical features were neglected. First, the history of TB made the doctors regard the pulmonary lesion as residual TB lesion. Second, TB is able to cause cyanosis and digital clubbing when severe hypoxemia occurs, which could explain the patient’s cyanosis and clubbed fingers since he was a child. We should draw lessons from this case that PAVMs should be suspected when the following combination of clinical manifestations coexists: central cyanosis, digital clubbing, hypoxemia, hemoptysis, elevated hemoglobin, pulmonary lesions on chest roentgenogram or CT, history of cerebral abscess and so on.
Echocardiography findings of PAVMs might suggest increased left heart volume overload. Chest roentgenogram could detect abnormal lesions in PAVMs region but with low specificity. CT pulmonary angiography is of great diagnostic value. Pulmonary angiography is regarded as the gold standard for diagnosis, especially when a therapeutic intervention is planned. In patients who are allergic to iodinated contrast, contrast-enhanced transthoracic echocardiography is highly recommended to be used as a diagnostic method, in which early appearance of microbubbles in the left atrium strongly suggests the existence of PAVMs .
The natural history of PAVMs is relatively predictable because of its tendency to increase in size. If untreated, the mortality rate of untreated symptomatic patients ranges from 4 to 22% and even up to 40% in severe cases . Spontaneous regression has rarely been reported.
There is consensus about early intervention in patients with PAVMs to prevent later complications like systemic embolization, pulmonary hemorrhage, ischemic stroke, cerebral abscess, congestive heart failure and so on. Treatment strategy of PAVMs should be made by taking multiple factors such as size, number, location and complications into consideration. Embolization is recommended as first-line treatment for PAVMs  while surgical lobectomy is recommended when PAVMs are diffuse, large and restricted to one lobe .