CT assessment of the adult extrathoracic trachea.

A total of 40 neck computed tomographic (CT) scans in adult patients were retrospectively reviewed and absolute measurements made of the anteroposterior (TRAP) and transverse (TRTR) air spaces at the first tracheal cartilage. For each patient, ratio measurements were calculated of the anteroposterior (TRAP/TC) and transverse (TRTR/TC) tracheal air space relative to the glottic air space at the true cord level. Mean TRAP (2.01 cm) and TRTR (1.84 cm) measurements for normal patients agreed closely with figures reported in prior cadaver preparation studies. The lower normal limit found for absolute tracheal diameter was 1.5 cm (TRAP) and 1.4 cm (TRTR), whereas lower normal limits for relative tracheal to glottic air space diameters were 0.7 (TRAP/TC) and 0.6 (TRTR/TC).