ASBESTOSIS, PLEURAL PLAQUES AND DIFFUSE PLEURAL THICKENING - 3 DISTINCT BENIGN RESPONSES TO ASBESTOS EXPOSURE

The aim of this study was to investigate by computed tomography (CT) w hether asbestosis, diffuse pleural thickening and/or pleural plaques a re statistically associated, We also tried to find criteria to differe ntiate between diffuse and circumscribed pleural thickening, From 231 exposed workers, only those subjects whose radiograph showed neither b ilateral calcified pleural plaques nor small pulmonary opacities highe r than 1/1 grade according to the 1980 International Labour Office (IL O) Classification were considered. Scans were assessed for the presenc e of subpleural curvilinear lines, septal and intralobular lines, pare nchymal bands, honeycombing, rounded atelectasis, pleural plaques and diffuse pleural thickening. CT scans revealed pleural and/or lung abno rmalities in 99 workers, Pleural plaques were unilateral in one-third of cases with plaques. Diffuse pleural thickening, parenchymal bands a nd rounded atelectasis were unilateral in, respectively, 62 and 69 and 75% of cases with the abnormality. Septal and intralobular lines, and honeycombing were always bilateral. CT signs could be grouped into th ree patterns: 1) septal and intralobular lines, and honeycombing corre sponding to pulmonary fibrosis; 2) pleural plaques col responding to p arietal pleural fibrosis; and 3) diffuse pleural thickening, rounded a telectasis and parenchymal bands corresponding to visceral pleural fib rosis, In these workers with a normal or near-normal radiograph, three groups of subjects with different responses were distinguished, Crow' s feet and rounded atelectasis help to differentiate plaques from diff use thickening.