PAVMs may be single or multiple, unilateral or bilateral, and simple or complex. Most solitary PAVMs are seen in the lower lobes, with the left lower lobe being the most common location followed by right lower lobe.4,5,11,26 The majority of multiple PAVMs are also confined to the lower lobes, with the incidence of bilateral PAVMs ranging from 8% to 20%.2,27 Simple PAVMs receive blood through a single artery, and complex PAVMs receive blood through two or more arteries (Figs 1B, 1C). The afferent supply is most often a branch of the pulmonary artery; however, in rare cases, it can derive from the systemic circulation, including the bronchial and intercostal arteries.26,27 In addition, PAVM may involve a large single sac or a plexiform mass of dilated vascular channels or consist of dilated and tortuous communications between artery and vein.2,28 The efferent limb of the PAVM often communicates with branches of the pulmonary vein, although direct communication with the inferior vena cava and the left atrium have been described.28 The abnormal segment between the pulmonary artery and the pulmonary vein is fragile and may rupture and bleed as the PAVM size increases and manifests as hemoptysis or hemothorax. Small subsets of patients have a more diffuse and severe type of PAVM that involves segmental pulmonary arteries. Diffuse PAVMs result in severe hypoxemia and are challenging to treat.