"Horseshoe" lung: report of five new cases.

A "horseshoe" lung is a rare congenital anomaly in which the posterobasal segments of the right and left lungs are fused behind the pericardial reflection at the cardiac apex. Most patients with such pulmonary fusion share many of those cardiovascular anomalies typical of the "scimitar" or hypogenetic right lung syndrome. The clinical diagnosis of horseshoe lung can be made by pulmonary angiography, which shows a branch of the right pulmonary artery originating from its proximal but inferior aspect and coursing into the left hemithorax. Thus, there are two conditions in which an artery from the right lung supplies part or all of the left lung: errant right pulmonary artery in the horseshoe lung deformity and so-called left pulmonary artery sling.