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

Progressive Massive Fibrosis. There are conglomerate soft-tissue densities in both upper lobes (black arrows) with linear scarring leading from the lower lobes (white arrows).

·         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