Silicosis (plural: silicoses) is a fibrotic pneumoconiosis caused by the inhalation of fine particles of crystalline silicon dioxide (silica). Occupations such as mining, quarrying, and tunnelling are associated with silicosis.
The disease occurs in two clinical forms that 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
In some situations, there is a rapid progression of the disease which is sometimes termed accelerated silicosis.
Radiographic findings on chest x-ray can consist of bilateral consolidation and/or ground-glass opacities, which tend to appear in perihilar regions.
CT findings include:
- numerous bilateral centrilobular nodular ground-glass opacities
- multifocal patchy ground-glass opacities
Chest radiograph shows 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 pulmonary nodules
- hilar and mediastinal lymphadenopathy, which 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
On a chest radiograph, complicated silicosis is usually indicated by large symmetric bilateral opacities that 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 potentially serious complications of silicosis.
Possible imaging differential considerations include:
- other pneumoconioses that may have a similar radiographic appearance