Figure 6b. Pulmonary hydatid embolism caused by rupture of a mediastinal hydatid cyst into the right pulmonary artery in a 22-year-old woman. The patient underwent pulmonary transplantation due to severe pulmonary arterial hypertension. (a) CT scan (5-mm collimation, lung window) obtained at the level of the left inferior pulmonary vein shows enlarged or engorged branches of the pulmonary arteries in the bilateral lower lung zones (arrows). (b) Photomicrograph (original magnification, x12; elastic stain) of the pathologic specimen shows a multilayered membrane of a hydatid cyst filling the pulmonary artery lumen.