Silicosis

·         Occupational Exposure

o       Free crystalline silica (quartz) or silicon dioxide from

§         Mining of coal, graphite, iron

§         Tin, Uranium, Gold

§         Silver, Copper

§         Also, sand blasters

§         Iron and steel foundry workers

§         Ceramic workers

§         Tunneling

·         Silicosis pathophysiology

o       Silica particles ingested by alveolar macrophages

o       Breakdown of macrophage releases enzymes which produce fibrogenic response

·         Silicosis natural history

o       Requires 10-20 years exposure before x-ray appearance

o       Radiographs frequently overestimate degree of symptoms early

o       Silicosis has a progressive nature despite cessation of dust exposure

·         Imaging findings

o       Multiple small rounded opacities 1-10 mm in size

o      Usually in upper lobes

§         Mostly in apical and posterior regions of upper lobes and apical portion of lower lobes

 

 

Silicosis features a diffuse micronodular lung disease
with an upper lobe predominance

 

o       May have ground-glass appearance

o       May occasionally calcify centrally (20%)

o       Lymph node enlargement common

§         Eggshell calcification of hilar nodes (5%)

·         DDx: Sarcoidosis

o       Large opacities are conglomerations of small opacities

·         Complicated Silicosis (Progressive Massive Fibrosis—PMF)

o       Massive fibrosis and conglomerate nodule formation in upper lobes with scarring and retraction of hila upwards

o       Conglomerate nodules are >1 cm in size

§         Usually in mid-zone or periphery of upper lobes

§         Compensatory emphysema occurs in lower lung fields

§         Nodules tend to disappear from rest of lung when PMF develops

o       Progressive Massive Fibrosis (PMF) may cavitate from tuberculosis or ischemic necrosis

·         Acute silicosis (silicoproteinosis)

o       From exposure to high concentrations of silica dust

o       Alveoli are filled with lipid-rich, PAS-positive material

o       Bilateral air-space disease with perihilar distribution

§         Imaging findings are similar to alveolar proteinosis

·         Caplan’s Syndrome

o       Consists of large necrobiotic nodules (rheumatoid nodules) superimposed on silicosis or coal worker’s pneumoconiosis (CWP)

§         More common with CWP

o       Other connective tissue diseases associated with silicosis

§          Scleroderma, RA, SLE

·         Silicosis Complications

o       Predisposes to TB

o       Exhibits “limited” evidence for carcinogenesis in humans