CT in silicosis: correlation with plain films and pulmonary function tests.

To investigate the usefulness of computed tomography (CT) in the qualitative and quantitative assessment of silicosis, CT scans, chest radiographs, and pulmonary function tests were obtained in 17 patients with silicosis and six controls. CT scans were graded for extent of silicosis visually and using mean attenuation values. The extent of associated emphysema was also determined. Extent of silicosis as assessed by CT was compared with extent estimated from the chest radiographs using the ILO 1980 classification and pulmonary function tests. Significant correlation was found between both the mean attenuation values (r greater than 0.62, p less than 0.001) and the visual CT scores (r greater than 0.84, p less than 0.001) compared with the ILO category of profusion. There was good inter- and intraobserver correlation for the visual CT grades of silicosis (r greater than 0.93, p less than 0.001). There was poor correlation between the pulmonary function tests and the nodular profusion on the chest radiograph and CT (r less than 0.50). Correlation was significant, however, between the CT emphysema score and both the FEV1% predicted (r greater than 0.66, p less than 0.001) and the diffusing capacity (r greater than 0.71, p less than 0.001). Using chest film assessment of the extent of silicosis, visual CT quantitation of silicosis is accurate and reproducible. Attenuation values were less reliable and their use is not recommended as an independent assessment of disease severity. The reduced levels of lung function in these patients correlated with superimposed emphysema rather than the nodular profusion. Emphysema associated with silicosis was easily detected on CT but not on the radiograph.