Prenatal diagnosis of left pulmonary artery sling and review of literature.

Left pulmonary artery sling (LPAS) is a very rare cause of large airway compression. In LPAS, the left pulmonary artery (LPA) arises from the proximal right pulmonary artery, coursing over the right mainstem bronchus, posterior to the trachea and anterior to the esophagus prior to reaching the left hilum. The aberrant course of the LPA results in anatomical obstruction of the right mainstem bronchus, the trachea, or both. Only a few reports present the prenatal features of LPAS. In this report, we present the prenatal diagnosis of a case of LPAS in one of a set of identical twins in which the only feature was that of an abnormal course of the LPA on 3-vessel tracheal view. The cross-sectional view at the level of three vessels which includes both pulmonary artery branches is useful to detect this abnormality. Color and power Doppler may be helpful as well.