Posterior mediastinal accessory thymus.

A rare case of accessory ectopic thymus in the right upper posterior mediastinum in a 40-day-old infant is described. The clinical presentation was that of tracheal obstruction. The compression and displacement of the trachea and the identification of the mass was enabled thanks to the high KV filtration technique. The mass was further identified by ultrasonography. Surgical removal of the accessory thymus relieved the tracheal obstruction.