Coal workers' pneumoconiosis (CWP) is an occupational disease (type of pneumoconiosis) caused by exposure to coal dust free of silica (washed coal). Histologically, CWP is classified according to disease severity into simple (presence of coal macules) and complicated (with progressive massive fibrosis) 3,7.
There are three main effects from carbon (inclusive of coal dust) on the lungs:
- anthracosis: relatively harmless deposition of carbon dust
- simple coal worker's pneumoconiosis (CWP)
- complicated coal worker's pneumoconiosis (progressive massive fibrosis): occurs in about of 10% of CWP and requires several years to develop
Despite histologic differences between silicosis and CWP, the two entities are not easily distinguished from one another on imaging studies.
Simple CWP appears as small (1-5 mm) round nodular opacities with an occasional appearance of reticular or reticulonodular opacities. Compared to nodules in silicosis, the nodules in CWP tend to have less well-defined margins and a more granular appearance.
Between 10-20% of patients with simple CWP have small central calcifications within these nodules on chest radiograph, which are contrasted to the more diffuse calcifications of silicosis 13-14. The eggshell calcification pattern pathognomonic of simple silicosis is seen in less than 2% of patients with simple CWP 13.
There is often a diffuse (typically perilymphatic) distribution of small nodules throughout the lungs, which tend to favor the upper lungs. About 30% of patients have calcifications with nodules on CT. Hilar or mediastinal lymph node enlargement has also been reported in 30% of patients 11.
Large opacities representing progressive massive fibrosis may be seen in complicated CWP. These fibrotic masses may either have irregular borders with associated surrounding emphysema, or regular borders without surrounding emphysema 11.
Lung cancer may present with a similar appearance, and differentiation is obviously important.
Compared with the signal intensity of muscle, complicated CWP appears as a low signal intensity lesion on both T1 and T2 weighted images. This is in contrast to neoplastic processes that have high signal intensity on T2 weighted images 8. On contrast administration, complicated CWP lesions frequently demonstrate peripheral enhancement 9.
The role of PET-CT in the diagnosis of malignancy in the setting of pneumoconiosis remains unclear, as both lung cancer and the fibrotic mass of complicated CWP may demonstrate increased uptake of FDG 10.
History and etymology
The first published case report on CWP was by Gregory (1831) in a British coal miner. For a period of time, the similarities on chest radiograph between silicosis and CWP lead to the hypothesis that CWP was a variant of silicosis. Further pathologic analysis has established CWP as a separate entity 1-2,5.
General imaging differential considerations include:
- 1. Collins EL, Gilchrist JC. Effects of dust upon coal trimmers. J Ind Hyg Toxicol 10:101-109 (1928).
- 2. Gough J. Pneumoconiosis of coal trimmers. J Pathol Bacteriol 51:227-285 (1940).
- 3. Churg A. Pathology of occupational lung disease. Regnery Publishing. (1998) ISBN:0683303864. Read it at Google Books - Find it at Amazon
- 4. Gregory JC. Case of particular black infiltration of the whole lungs resembling melanosis. Edinburgh Med Surg 36:389-394 (1831).
- 5. Heppleston AG. The essential lesion of pneumoconiosis in Welsh coals workers. J Pathol Bacteriol 59:453-460 (1947).
- 9. Matsumoto S, Mori H, Miyake H et-al. MRI signal characteristics of progressive massive fibrosis in silicosis. Clin Radiol. 1998;53 (7): 510-4. Pubmed citation
- 10. O'Connell M, Kennedy M. Progressive massive fibrosis secondary to pulmonary silicosis appearance on F-18 fluorodeoxyglucose PET/CT. Clin Nucl Med. 2004;29 (11): 754-5. Clin Nucl Med (link) - Pubmed citation
- 11. Remy-Jardin M, Degreef JM, Beuscart R et-al. Coal worker's pneumoconiosis: CT assessment in exposed workers and correlation with radiographic findings. Radiology. 1990;177 (2): 363-71. Radiology (abstract) - Pubmed citation
- 12. Remy-Jardin M, Remy J, Farre I et-al. Computed tomographic evaluation of silicosis and coal workers' pneumoconiosis. Radiol. Clin. North Am. 1992;30 (6): 1155-76. Pubmed citation
- 13. Williams JL, Moller GA. Solitary mass in the lungs of coal miners. Am J Roentgenol Radium Ther Nucl Med. 1973;117 (4): 765-70. Am J Roentgenol Radium Ther Nucl Med (abstract) - Pubmed citation
- 14. Young RC, Rachal RE, Carr PG et-al. Patterns of coal workers' pneumoconiosis in Appalachian former coal miners. J Natl Med Assoc. 1992;84 (1): 41-8. Free text at pubmed - Pubmed citation
- 15. 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
- 18. Laney AS, Weissman DN. Respiratory diseases caused by coal mine dust. (2014) Journal of occupational and environmental medicine. 56 Suppl 10: S18-22. doi:10.1097/JOM.0000000000000260 - Pubmed
- 18. Heppleston AG. The pathogenesis of simple pneumoconiosis in coal workers. J Pathol Bacteriol 67:51-63 (1954).
- 19. Cox CW, Rose CS, Lynch DA. State of the art: Imaging of occupational lung disease. (2014) Radiology. 270 (3): 681-96. doi:10.1148/radiol.13121415 - Pubmed
- 17. Kleinerman J, Green FHY, Harley R, Lapp NL, Laqueur W, Naeye RL, Pratt P, Taylor G, Wyatt J. Pathology Standards for Coal Workers' Pneumoconiosis: Report of the Pneumoconiosis Committee of the College of American Pathologists to the National Institute for Occupational Safety and Health. Arch Pathol Lab Med 103:375-431 (1978).
- 16. Matsumoto S, Miyake H, Oga M et-al. Diagnosis of lung cancer in a patient with pneumoconiosis and progressive massive fibrosis using MRI. Eur Radiol. 1998;8 (4): 615-7. Eur Radiol (link) - Pubmed citation