Pulmonary artery webs: Chronic pulmonary thromboembolism

Pulmonary artery bands and webs are fibrotic structures anchored to the vessel wall of the pulmonary arteries, thought to arise as an uncommon consequence of chronic organized pulmonary embolism. On CT Angiography, webs appear as thin linear filling defects surrounded by contrast. The webs in pulmonary arteries are unusual in that two types of animal related webs may occur (i.e. the webbing of a duck’s foot which are also called shelves, or a spider’s web). Webs are more often seen in the distal lobar or segmental arteries. Complete clearance of emboli is usually not achieved after an acute pulmonary thromboembolism. Approximately 2.4% of patients with acute pulmonary embolism will go on to develop chronic thromboembolic pulmonary hypertension (CTEPH), although at least 25% of patients with CTEPH have no history of symptomatic pulmonary embolism. Risk factors for CTEPH include prothrombotic conditions, a history of massive PE, and older age.