CT of saber-sheath trachea. Correlation with clinical, chest radiographic and functional findings

The diagnosis of saber-sheath trachea is easy at CT due to its cross-sectional imaging, but the significance of this CT sign has not been evaluated in the diagnosis of chronic obstructive pulmonary disease (COPD). Various signs of COPD were compared between a series of 20 patients with a saber-sheath trachea at CT (tracheal index < or = 66%) and a group of 20 pneumologic control patients without saber-sheath trachea (tracheal index > or = 70%). These signs included clinical and standard radiographic indices of COPD, sternum-spine distance and 3 functional tests of COPD: forced expiratory volume in one second, carbon monoxide diffusing lung capacity, and functional residual capacity (FRC). A significant difference was found between the 2 groups, concerning the values of FRC (p < 10(-4)) and of sternum-spine distance (p < 10(-2)). The tracheal index was significantly correlated with the FRC values (r = -0.611; p < 10(-5)) and with the sternum-spine distance (r = -0.322; p < 0.05). No other significant difference was observed. It is concluded that saber-sheath trachea is basically a sign of hyperinflation.