Thin-Section CT Findings of Arc-Welders’ Pneumoconiosis Using a scale graduated in multiples of ten percent, the extent of abnormalities was visually assessed; 20 30%, for example, indicated that micronodules or ground-glass at- tenuation occupied 20 30% of the area of lung parenchy- ma seen in the images. Using Spearman’s correlation, the extent of abnormalities was statistically correlated with the results of pulmonary function tests (FEV1/FVC% and FVC) and the degree of dyspnea (NYHA class 0 to 4). If the findings of thin-section CT were positive, these were correlated with smoking history (Spearman’s correlation). RESULTS Among 53 welders who answered to the questionnaire, 42 (79%) were smokers with a 1 to 30 (mean, 13) pack- year history, and 46 had symptoms such as dyspnea (n = 40), sputum (n = 33), and cough (n = 25). In 54 of 85 welders (64%), the findings of thin-section CT scanning were positive. The most common finding was poorly-defined centrilobular micronodules (n = 30) (Fig. 1), followed by branching linear structures (n = 18) (Fig. 2), and ground-glass attenuation (n = 6) (Fig. 3). While many cases of poorly-defined micronodules (17/30) and branch- ing linear structures (10/18) showed slight upper zonal pre- dominance, and were less commonly randomly distributed (7/30 for poorly-defined micronodules, 6/18 for branching linear structures), ground-glass attenuation was (in 5/6 cas- es) randomly distributed between upper and lower lung zones, As far as central or peripheral distribution was con- cerned, centrilobular micronodules and branching linear structures showed neither central nor peripheral predomi- nance. Ground-glass attenuation was distributed more cen- trally (4/6). The extent of abnormalities was 0 10% in 29 cases, 10 20% in 11, 20 30% in seven, 30 40% in four, and more than 40% in three. Other thin-section CT findings in welders included local- ized stable tuberculous lesions (n = 10), bronchial dilata- tion or wall thickening (n = 8), localized emphysema (n = 5), noncalcified mediastinal lymphadenopathy (n = 2), sub- segmental atelectasis (n = 2), or tracheal dilatation (n = 1). In particular, in no patient was the appearance of emphy- sema compatible with so-called focal dust emphysema. In the smokers’ group, thin-section CT findings in six pa- tients (14%) were positive. The predominant finding was poorly-defined micronodules in four, branching linear structures in one, and ground-glass attenuation in one. In Fig. 2. 42-year-old man with a 20 pack-year smoking history and 14 years exposure to arc-welding. Pulmonary function tests were normal. Thin-section CT scan obtained at the level of the left lower lobar bronchus shows branching linear structures (arrows). According to visual assessment, the extent of abnormalities was 20-30%. Korean J Radiol 1(2), June 2000 Fig. 3. 46-year-old man for whom smoking and exposure history were not available. Thin-section CT scan obtained below the carina shows areas of ground-glass attenuation. Visual assessment revealed that extent of abnormalities was 70-80%. 81