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Silicosis: Expiratory Thin-Section CT Assessment of Airway Obstruction¹

¹ From the Department of Radiology, Dokkyo University School of Medicine, 880 Kita-Kobayashi, Mibu, Tochigi 321-0293, Japan (H.A., M.F.); Department of Radiology (P.A.G.) and Statistical Unit, Institute of Interdisciplinary Research in Human and Molecular Biology, Hôpital Erasme, Université Libre de Bruxelles, Belgium (V.D.M.); and Departments of Radiology (H.S., H.M.) and Respiratory Medicine (Y.S.), Labour Welfare Hospital for Silicosis, Tochigi, Japan. Received September 17, 2004; revision requested November 24; revision received December 6; accepted January 17, 2005. Address correspondence to H.A. (e-mail: arakawa{at}dokkyomed.ac.jp).

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]: = –0.632, P < .001; forced expiratory flow at 50% of the FVC: = –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.

© RSNA, 2005