Computed tomography of the tracheal bronchus.

Tracheal bronchus is an uncommon anomaly in which an ectopic bronchus arises from the trachea above the carina. It occurs on the right side and two types are described: "supernumerary," which is associated with a normal trifurcating right upper lobe bronchus, and "displaced," in which instance the ectopic bronchus supplies the apical segment of the upper lobe. The CT appearance of this anomaly is described in two cases. Findings include identification of a bronchus arising from the trachea in a section more cephalad than the carina and the presence of only two segmental bronchi arising from the anatomic right upper lobe bronchus when the anomaly is of the "displaced" type. Thin axial sections and coronal imaging display the tracheal bronchus to best advantage.