In vivo and in vitro morphometry of the human trachea.

Most morphometric studies of the human trachea have relied on plain radiographs with their attendant limitations. Reports using computed tomography (CT) have focused on the growing trachea or one particular dimension. The aim of this study was to document the morphometry of the adult trachea in vivo using high-resolution chest CT scans, supplemented by data from cadavers. Sixty anonymised high-resolution chest CT scans (aged 22-88 years, 40 males) were analyzed. Scans were performed using a standardized breath-holding technique in patients with no distorting intrathoracic pathology. Standardized tracheal measurements included: length, maximum antero-posterior and transverse diameters, volume, subcarinal angle, and carinal position in relation to the tracheal midline. Measurements were also made in 10 cadaver tracheas (aged 68-101 years, 7 males). CT data showed that mean tracheal length (males 105.1 +/- 9.8 mm, females 98.3 +/- 8.7 mm), maximum antero-posterior and transverse diameters, and tracheal volume (males 35.6 +/- 6.8 cm3, females 24.7 +/- 6.1 cm3) were all significantly greater in men (P < or = 0.01). The subcarinal angle was very variable (mean 78 +/- 20 degrees , range 36-121 degrees ) and showed no correlation with age or gender. The carina was sited to the left of the tracheal midline in 49 (81%) patients. Cadaver tracheas had 14-19 tracheal rings and the posterior membranous trachea was wider in men (17.7 +/- 4.4 mm vs. 11.8 +/- 3.0 mm, P = 0.07). In conclusion, there is marked sexual dimorphism in the morphometry of the human trachea. The variation in adult tracheal dimensions in vivo is greater than in standard descriptions. These data may be valuable when interpreting chest CT scans and when calculating respiratory dead space.