Study Syllabus for Classification of Radiographs of Pneumoconioses
Pathology Overview
Pathology Basis of Occupational Lung Disease
Asbestos-Related Pleuropulmonary Disease
In the ILO Classification, asbestosis is usually characterized by the development of small irregular opacities (s, t, u). In approximately 20% to 30% of cases, parenchymal changes are accompanied by pleural thickening with or without calcification. Rounded opacities are rarely seen in the chest radiographs of patients with asbestosis unless there has been additional exposure to silica. Progression of asbestosis may be seen radiographically as honeycomb change [Morgan and Gee 1995; Gefter et al. 1984].
Pleural changes due to asbestos exposure are identified more frequently on chest radiography than is parenchymal disease. Asbestos-related pleural effusion progressing to diffuse pleural thickening (fibrothorax) may create a ground-glass haze over the lung, associated with an obliterated costo-phrenic angle. With significant pleural fibrosis the rib spaces are crowded and there is ipsilateral loss of lung volume. Pleural plaques appear on the chest wall or diaphragm as smooth, regular linear shadows. En face plaques can closely mimic the parenchymal changes of asbestosis. Rounded atelectasis appears as a spherical or elliptical subpleural pleural-based opacity. Vessels and bronchi from the hilar region converge on the area of atelectasis, forming the “comet-tail” sign. There is pleural thickening overlying the region of atelectasis, which can simulate a lung tumor [Morgan and Gee 1995; Gefter et al. 1984].
There are no distinctive radiologic features of lung carcinoma caused by asbestos exposure. There is a tendency, however, for increased lower-lobe distribution of asbestos-related lung cancers. Within the lower lobe, asbestos-related lung carcinomas are frequently peripherally distributed. In the presence of dense parenchymal fibrosis, radiographic detection of a neoplasm may be difficult [Gefter et al. 1984]. Attribution of a carcinoma to asbestos is supported by a significant cumulative exposure history and/or, from the pathological perspective, an elevated asbestos burden in the lung parenchyma, as assessed by asbestos bodies or fiber counts.
Finally, mesothelioma usually presents as a large unilateral pleural effusion. Pleural-based solid lesions may also occur in a minority of patients. With progression, tumor replaces pleural effusion, which often becomes loculated [Morgan and Gee 1995; Gefter et al. 1984].