Silicosis: Expiratory thin-section CT assessment of airway obstruction

PURPOSE: To prospectively evaluate if findings on paired inspiratory and expiratory thin-section computed tomographic (CT) scans in patients with silicosis correlate with pulmonary function test results. MATERIALS AND METHODS: Institutional review board approval and patient consent were obtained. Thirty-seven men (mean age, 71 years; range, 53-88 years) with silicosis were included. All patients had undergone inspiratory and expiratory thin-section CT and spirometry. Silicotic nodules, large opacity, emphysema, reticular opacities, bronchiectasis, and air trapping were graded subjectively on CT images. Emphysema was quantified on these images with built-in software. CT numbers were correlated with spirometric findings by using Spearman rank correlation analyses. Ten healthy volunteers (three men and seven women; mean age, 58 years) served as control subjects. RESULTS: After exclusion of three patients with inadequate image quality, 34 patients (mean age, 70 years; range, 53-88 years) were enrolled in the study group. Spirometric values did not differ significantly between patients with simple (n = 20) and patients with complicated (n = 14) silicosis but were significantly lower in patients than in control subjects. CT findings included air trapping (n = 33), emphysema (n = 26), nodules (n = 32), bronchiectasis (n = 22), large opacity (n = 19), and reticulation (n = 5). The extent of both air trapping and emphysema correlated negatively with spirometric values; the air trapping score showed the strongest correlation (ratio of forced expiratory volume in 1 second to forced vital capacity [FVC]: rho = -0.632, P < .001; forced expiratory flow at 50% of the FVC: rho = -0.576, P = .001). Silicotic nodule, large opacity, and bronchiectasis scores did not correlate with obstructive functional impairments. CONCLUSION: In comparison with the spirometric value, the extent of air trapping proved the best CT index in the assessment of obstructive derangement in workers with exposure to silica dust. (c) RSNA, 2005.