Pulmonary artery, Pulmonary arterial thromboembolism

A blood clot in the pulmonary artery is a life-threatening condition, often arising as a complication of deep vein thrombosis (e.g. of an immobilized leg). The cause of the thromboembolus was not specified in this case. Sections from the lung depict a pulmonary arterial thromboembolus. Features of recent formation include red blood cells layered with fibrin and platelets (lines of Zahn) and can be contrasted with older thromboembolus which show features of organization including cellular infiltration (macrophages and neovessels) found at the edges and progressing inward.