Silicosis

Pathophysiology:  An occupational lung disease due to the inhalation of silica (silicon dioxide crystals).  The silicon dioxide crystals lead to a non-immunologic granulomatous inflammatory reaction with resulting destruction of alveolar walls and the lung interstitium. The inflammatory response is characterized by granulomata, nodules, fibrosis, and reactive hilar and mediastinal adenopathy.

An unusual variant: acute silicoproteinosis occurs with massive exposure to silica in sandblasters.  The alveoli fill rapidly with desquamated epithelial cells and a surfactant-like substance. The process simulates other air space diseases and alveolar proteinosis.

Clinical Clues: always an occupational history of mining or silica exposure.

Almost always in males (social reasons).

CXR/CT Findings:

Simple Silicosis:

1. distinct upper 2/3 lung predilection (due to mechanics of air flow and lymphatic drainage)

2. small to medium sized nodules and linear interstitial lung changes

3. characteristic central hilar and mediastinal adenopathy, often with egg-shell calcifications

4. may progress to marked fibrosis, hilar retraction and lung distortion

Complicated Silicosis (see progressive massive fibrosis):

1. PMF

2. Tuberculosis (due to social conditions of mining and ease of spread)

3. Scar carcinoma (adenocarcinoma of lung), rarely

“Aunt Sophies”:  DDx of upper lung, small nodular disease.

1. Granulomatous lung diseases: TB, atypical TB, fungal diseases, sarcoidosis, eosinophilic granuloma
2. Metastases: eg. thyroid, mucinous adenocarcinomas, melanoma, breast cancer
3. Smaller airways disease: eg. bronchiectasis