The right paratracheal stripe.

The right paratracheal stripe (RPS) is seen on postero-anterior chest radiographs as a thin, water-density stripe between the air column of the trachea and the adjacent right lung. The range of width of the RPS in 1,259 normal subjects was 1 to 4 mm. An RPS width of 5 mm or more is reliable evidence of disease. The differential diagnosis of this finding is lengthy, and best divided into those diseases affecting the (a) trachea; (b) mediastinum; and (c) pleura.