Normal position of trachea and anterior junction line on CT

In unilateral diseases of the chest accompanied by either volume loss or expansion there is mediastinal shift and mediastinal "herniation" of one lung into the opposite hemithorax. This may also be accompanied by changes in the size of the hemithoraces. Although early detection of these changes may be difficult on chest radiography, one can detect all these changes on CT with greater ease. Since the normal range of position of the mediastinal structures on CT and the symmetry of the hemithoraces have not been studied before, we conducted a prospective study of normal chest CT to define the range of position of the trachea and the anterior junction line, as well as the normal range of differences in the parasagittal diameters of the two hemithoraces.

The trachea was < or = 1.6 cm to the right and 0.7 cm to the left of midline; the anterior junction line was < or = 1 cm to the right and 2 cm to the left. The hemithoraces were asymmetric in 84%, with the difference in the parasagittal diameters of the two hemithoraces < or = 1.5 cm.

These data may help radiologists detect subtle mediastinal shifts and asymmetry in patients with unilateral pleural or pulmonary disease.