Silicosis occurs in two clinical forms: acute silicosis and classic silicosis.

In certain instances, the disease may exhibit swift advancement, often referred to as accelerated silicosis (a form of rapidly progressive pneumoconiosis).

Acute Silicosis

Acute silicosis is less frequently seen and manifests as alveolar silicoproteinosis. It develops after exposure to high concentrations of respirable crystalline silica and results in symptoms within weeks to a few years after the initial exposure.

Radiological findings can consist of large bilateral perihilar consolidation or centrilobular nodular ground glass opacities in perihilar regions, often with no septal thickening.

Classic Silicosis

Classic silicosis is more prevalent than the acute form and can be categorized as either simple or complicated depending on its imaging presentation. Typically manifests 10 to 20 years following initial exposure, and it is not unusual for the radiographic signs of silicosis to become evident many years after the cessation of employment in a job associated with exposure.

Simple Silicosis

Imaging findings of simple silicosis include multiple small pulmonary nodules, predominant in the posterior upper lungs with a perilymphatic distribution, ranging from 1 to 10 mm in diameter.

Fig 1: Plain chest radiograph shows multiple small bilateral nodular opacities, well-defined and uniform in shape, predominantly located in the upper lobes.

Fig 2: Classic simple silicosis. High-resolution CT scan shows multiple bilateral small nodules, predominantly in the upper lobes.

Hilar and mediastinal lymphadenopathy may precede the appearance of nodular lesions and can have calcifications, typically at the periphery of the node. An “eggshell” calcification pattern is highly suggestive of silicosis.

Fig 3: “Eggshell” lymph nodes calcification. CT (mediastinal window) shows mediastinal lymph nodes calcified in the periphery. This pattern is highly suggestive of silicosis.

Complicated silicosis

Complicated silicosis occurs when small nodules in simple silicosis coalesce into larger conglomerates with a diameter of 10 mm or more, a condition characterized by progressive massive fibrosis (PMF), whose features include large mass-like conglomerates, often with irregular or ill-defined margins and calcifications, irregular reticulation, and traction bronchiectasis.

Fig 4: Classic complicated silicosis. Plain chest radiograph shows bilateral reticulonodular opacities in the upper lobes, with scattered mass-like lesions. There is loss of volume of the right lung and ipsilateral mediastinal shift.

Fig 5: Classic complicated silicosis. Axial and coronal CT images (lung window) of the patient above show large mass-like conglomerates of fibrosis, with irregular margins, associated with architectural distortion and bronchiectasis. This appearance is most characteristic of progressive massive fibrosis.

Fig 6: Classic complicated silicosis. High-resolution CT demonstrates upper zone predominant nodularity with coalescence into large mass-like conglomerates, associated with architectural distortion, paracicatricial emphysema and bronchiectasis (A, B) consistent with progressive massive fibrosis. Symmetric mediastinal and hilar lymphadenopathy with “eggshell” calcification is present (C).

Peripheral nodules may coalesce into pseudoplaques, mimicking pleural disease. Parenchymal retraction around nodules may cause paracicatricial emphysema. Progressive massive fibrosis is more likely to occur in silicosis than other pneumoconiosis.

Accelerated silicosis

Accelerated silicosis has emerged over the last 10 years relating to the use of artificial stone. In contrast to chronic silicosis, the disease manifests soon after exposure (4-10 years) and carries a poor prognosis. Accelerated silicosis is recognised by a typically high proportion of small, centrilobular ground glass nodules. There are often no solid nodules. Ground glass may also be present as a patchy/regional infiltrate.

Associated diseases

Silicosis is associated to various conditions, including mycobacterial and fungal infections, airflow obstruction, chronic bronchitis, autoimmune diseases, chronic kidney disease, and lung malignancy.

Silicotuberculosis

Mycobacterial infections, especially tuberculosis, have long been acknowledged as well-established complications of silicosis. Such infections should be consistently considered when a patient with silicosis experiences constitutional symptoms, deteriorating respiratory function and haemoptysis. Serial imaging findings comparison, with a focus on identifying asymmetric nodules, consolidation, effusions, cavities, and any signs of focal or rapid deterioration, is recommended.

Fig 7: Pulmonary silicosis complicated by tuberculosis. Plain chest radiograph (A) shows cavitary lesion (circle) in left upper lung and multiple small bilateral nodules in both lungs. Coronal (B) and axial (C and D) CT images show bilateral multiple small lung nodules, along with hilar and mediastinal lymphadenopathy. Additionally, there is a cavitary lesion identified in the superior left lobe, accompanied by surrounding lung consolidation and bronchiectasis (arrow).

While cavitation is a significant marker suggesting probable silico-tuberculosis, it can also result from ischemic changes in a fibrotic mass associated with silicosis.

Autoimmune diseases

Crystalline silica is implicated not only in the development of silicosis but also in the onset of other autoimmune diseases such as systemic lupus erythematosus, rheumatoid arthritis-Caplan syndrome, systemic sclerosis, and antineutrophil cytoplasmic antibody (ANCA)-related vasculitis.

Fig 8: Pulmonary silicosis complicated by microscopic polyangiitis. Plain chest radiograph (A) shows multiple small bilateral nodular opacities, as observed in classic simple silicosis, and bilateral widespread consolidation, as a diffuse pulmonary haemorrhage finding. Coronal (B) and axial (C) CT images show multiple small nodules. Bilateral ground glass opacities and areas of consolidation are shown in relation to pulmonary haemorrhage, seen in vasculitis with pulmonary involvement.

The occurrence of systemic sclerosis following exposure to silica, with or without concurrent silicosis, is termed Erasmus syndrome. The clinical manifestations of systemic sclerosis vary and typically involve pulmonary and oesophageal changes, most commonly presenting as interstitial lung disease (nonspecific interstitial pneumonia pattern) and oesophageal dilation on CT.

Fig 9: Erasmus syndrome: association of silica exposure and systemic sclerosis. Axial and coronal CT images (lung window) show bibasilar ground-glass opacities with subpleural sparing, suggesting non-specific interstitial pneumonia (NSIP). Oesophageal dilatation is also present (arrow). These findings are associated with systemic sclerosis. Bilateral peripheral nodules, upper lobe predominant, some forming conglomerates, are seen as silicosis findings.

Fig 10: Erasmus syndrome: association of silica exposure and systemic sclerosis. Plain chest radiograph (A) shows multiple small bilateral nodular opacities, well-defined and uniform in shape. High-resolution CT scan (B) shows multiple small nodules, as classic simple silicosis findings. Basilar symmetrical reticular and ground-glass opacities and a dilated oesophagus is also shown.