Silicosis is a fibrotic pneumoconiosis that is caused by the inhalation of fine particles of crystalline silicon dioxide (silica). Occupations such as mining, quarrying, and tunneling are associated with silicosis.
The disease occurs in two clinical forms which are subdivided by their temporal relationship to the exposure to silica:
- acute silicosis - manifests as alveolar silicoproteinosis
- classic silicosis - manifests as a chronic interstitial reticulonodular disease
The classic form is much more common than the acute form and can be classified as simple or complicated, according to the radiographic findings:
- simple silicosis : pattern of small and round or irregular opacities
- complicated silicosis : large conglomerate opacities that equate to progressive massive fibrosis
Plain film / Chest x-ray
Radiographic findings can consist of bilateral consolidation and / or ground glass opacitiy, which tend to appear in perihilar regions.
CT findings include
- numerous bilateral centrilobular nodular ground-glass opacities,
- multifocal patchy ground-glass opacities, and
Classic - simple silicosis
Plain film / Chest x-ray
Radiographic findings are multiple nodular opacities:
- well defined and uniform in shape and attenuation
- ranging from 1 to 10 mm in diameter
- predominantly located in the upper lobe and posterior portion of the lung.
- calcification of nodules is seen on chest radiographs in 10 - 20% of patients.
At CT, features of simple silicosis include :
- multiple small nodules that are upper lobe predominant and accompanied by calcifications
- hilar and mediastinal lymphadenopathy : may precede the appearance of parenchymal nodular lesions
- calcification of lymph nodes : common and typically occurs at the periphery of the node. This eggshell calcification pattern is highly suggestive of silicosis.
Classic complicated silicosis
Plain film / chest x-ray
On a chest radiograph, complicated silicosis is usually indicated by large symmetric bilateral opacities which are
- 1 cm or more in diameter and with an irregular margin
- commonly in the middle lung zone or peripheral one-third of the lung
- gradually migrating toward the hilum, leaving emphysematous lung tissue between the fibrotic tissue and the pleural surface.
CT features are focal soft-tissue masses, often with irregular or ill-defined margins and calcifications, surrounded by areas of emphysematous change.
Treatment and prognosis
Treatment is to remove the exposure, although silicosis may progress despite removal from the dust environment.
In acute silicosis particularly, the clinical course is usually progressive and ends in death due to cor pulmonale and respiratory failure therapy with corticosteroids
Carcinoma and tuberculosis are potential serious complications of silicosis.
- Other pneumoconioses which may have a similar radiographic appearance:
- 1. Chong S, Lee KS, Chung MJ et-al. Pneumoconiosis: comparison of imaging and pathologic findings. Radiographics. 26 (1): 59-77. doi:10.1148/rg.261055070 - Pubmed citation
- 2. Bergin CJ, Müller NL, Vedal S et-al. CT in silicosis: correlation with plain films and pulmonary function tests. AJR Am J Roentgenol. 1986;146 (3): 477-83. AJR Am J Roentgenol (abstract) - Pubmed citation
- 3. Bégin R, Bergeron D, Samson L et-al. CT assessment of silicosis in exposed workers. AJR Am J Roentgenol. 1987;148 (3): 509-14. AJR Am J Roentgenol (abstract) - Pubmed citation
- 4. Kim KI, Kim CW, Lee MK et-al. Imaging of occupational lung disease. Radiographics. 2001;21 (6): 1371-91. Radiographics (full text) - Pubmed citation