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.