The posterior tracheal band in the lateral chest radiograph.

: The appearance and variations of the posterior tracheal band (PTB) was studied from 406 upright chest radiographs, taken from 293 individuals of varying age. PTB is visualized in about 80% of individuals well enough to be diagnostically useful. Its average width is 3 mm, and patient positioning can cause variations not exceeding 2 mm. Progressive widening by 2 mm or more, blurring of previously sharp margins or an overall width exceeding 5 mm should be considered suggestive of mediastinal or related abnormality.