CT assessment of the adult intrathoracic cross section of the trachea.

After phantom validation of the method, normal tracheal morphology of 25 women and 25 men was studied retrospectively at level 1, the thoracic inlet; level 2, the supracarinal level, and level 3, halfway between. In no case was the minimal cross-sectional area less than 68% of the maximum of the three levels. Areas at the same level were different depending on sex, but not on other body parameters, and so were the means of the three levels: 194 mm2 (SD 35) in women and 272 mm2 (SD 33) in men. Mean tracheal area correlated with mean tracheal diameter (r = 0.98). Average configuration of the trachea was sagittal at the thoracic inlet and transverse supracarinally. Absolute tracheal cross sections of less than 120 mm2 in women and 190 mm2 in men and relative values of less than two-thirds compared with other levels should suggest an abnormality. Although static and not in competition with functional tests, noninvasive CT area calculation may be useful in demonstrating and quantifying tracheal obstruction when mediastinal neoplasms are staged or as a complementary morphological test when ventilatory studies do not afford enough information to localize the lesion and to decide about treatment.