Han et al. all subjects, the extent of abnormalities was 0 10%. Other findings included localized bronchiectasis (n = 12), stable tuberculosis (n = 11), nodules or mass (n = 11), localized emphysema (n = 10), pleural thickening (n = 7), bulla (n = 4), consolidation (n = 3), fungus ball (n = 2), or lobar col- lapse (n = 1). Among 53 welders who answered the questionnaire, the rate of positive thin-section CT findings was 57.1% for smokers (24/42) and 54.5% for non-smokers (6/11). The extent of abnormalities seen on thin-section CT showed no significant correlation with the results of pulmonary func- tion tests (for FEV1/FVC, r = -0.045, p = .747; for FVC, r = 0.082, p = .55, respectively), with the degree of dyspnea (r = 0.023, p = 1), or with longevity of smoking (r = .0123, p = .949). DISCUSSION Arc-welders’ pneumoconiosis is caused by the deposition of iron oxide, Fe2O3. Since the original description of the condition in 1936, it has been generally assumed that the disease is a benign one, not associated with respiratory symptoms or fibrosis. Some authors, however, reported res- piratory difficulty associated with arc-welding (6), or histo- logic findings of emphysema or pulmonary parenchymal fi- brosis in arc welders (7, 8). Here, the rare occurrence of parenchymal fibrosis has been attributed to ingredients other than iron (mostly silica) in welding fumes (9), based on cases where heavy deposition of iron in lung parenchy- ma was not associated with pulmonary fibrosis in either a human (10) or in experimental animal model (11). Indeed, in none of our cases with extensive ground-glass attenua- tion, which possibly represented the accumulation of large amount of iron oxide, was emphysema observed on thin- section CT scans. Likewise, we strongly doubt that in a study by Akira et al. (4), the emphysema revealed by thin- section CT scanning of seven welders with a smoking histo- ry was work related. Other thin-section CT findings in their study coincided with those in ours. In our study, the predominant finding was centrilobular microndules, and this can be explained by reference to pre- vious studies in which histological examinations were per- formed (13 14). They described the presence of pigmented macrophages in air spaces and interstitium close to the cen- ter of the acinus, with occasional fibrosis around pigment- ed deposits in these areas. Our findings appeared similar to those of smokers’ lung (14), and this similarity may be due to similarities in the pathologic findings of both entities. Small-airway lesions in patients with histories of exposure to nonasbestos dusts consist of deposits of fibrous tissue, often accompanied by 82 pigment, in the walls of membranous and respiratory bron- chioles and alveolar ducts (15, 16). In addition, the fact that 79% of the welders were smokers might call it into question whether the findings in our study truly represent- ed exposure to welding and were not the results of smok- ing. On the basis of the following facts, however, we sug- gest that the findings in our subjects are mostly due to ex- posure to arc-welding. First, while there was a significant difference in the positive rate of CT findings between the welders (64%) and the smokers (14%), no such difference was seen in the positive rates for welders who smoked (57.1%) and those who did not (54.5%); second, among welders, there was no statistically significant dose-response relationship between smoking history and the extent of ab- normalities. Our study suffers from certain limitations. For example, those who interpreted the CT findings were not blinded as to whether a particular scan belonged to the welders’ or the smokers’ group. Thus, we admit that image interpreta- tion for the latter could have been subject to prejudice, though not to the extent of significantly affecting the re- sults of our study. Another limitation is that because most of the patients in our study sought compensation, they may have exaggerated the extent of their clinal symptons, and this may have diminished the statistical accuracy of our findings. In conclusion, thin-section CT findings of arc-welder’s lung include poorly-defined centrilobular micronodules, branching linear structures, and ground-glass attenuation. Some of our cases in which extensive abnormalities were not associated with the development of emphysema seem to indicate that this condition of emphysema is not caused by inhalation of arc-welding fumes. Since the CT findings in welder’s lung can sometimes be very extensive, we be- lieve that in order not to mistakedly perceive evidence of more serious conditions other than actually existing arc- welders’ lung, cautious interpretation is required. References 1. Doig AT, McLaughlin AIG. X-ray appearance of the lungs of electric welders. Lancet 1936;1:771-775 2. Attfield MD, Ross DS. Radiological abnormalities in electric-arc welders. Br J Ind Med 1978;35:117-122 3. Lee JB, Kim KI, Chang HS et al. Radiologic findings of chest ra- diograph for the mass survey in shipyard welders, Pusan. J Korean Radiol Soc 1990; 26:82-90 4. Akira M. Uncommon pneumoconiosis: CT and pathologic find- ings. Radiology 1995;197:403-409 5. Austin JH, Muller NL, Friedman PJ et al. Glossary of terms for CT of the lungs: Recommendations of the Nomenclature Committee of the Fleischner Society. Radiology 1996;200:327- 331 6. Charr R. Respiratory disorders among welders. Am Rev Tuberc Korean J Radiol 1(2), June 2000