Silicosis, Simple

Melinda Z. Rixey, MD

Aqeel A. Chowdhry, MD

Tan-Lucien H. Mohammed, MD, FCCP

Key Facts

Terminology

Simple pneumoconiosis: Micronodules < 1 cm develop more than 10 years after long-term occupational exposure
Acute silicoproteinosis
- Rare fulminant respiratory complication of intense exposure to silica dust (typically sandblasting)
- Appears within 6 months to 3 years after initial exposure
Caplan syndrome
- Seropositive rheumatoid arthritis associated with pneumoconiosis (coal, silica, or asbestos)

Imaging Findings

Micronodules < 10 mm in centrilobular and subpleural distribution
More profuse in dorsal aspect of upper lobes, right side more severely involved than left
Silicoproteinosis: May have “crazy-paving” pattern (identical to alveolar proteinosis)
Symmetric enlargement (75%) of hilar and mediastinal lymph nodes, generally < 3 cm in diameter
Patterns of calcification: Punctate > diffuse > “eggshell”
Caplan syndrome
- Multiple large nodules usually < 5 cm in diameter (may cavitate or calcify)

Top Differential Diagnoses

Axial CECT shows upper lobe predominant centrilobular and subpleural nodules

in the dorsal aspect of the lung in this patient with simple silicosis.

Axial HRCT in the same patient more inferiorly shows centrilobular nodules

and subpleural nodules

, primarily in the dorsal lungs.

TERMINOLOGY

Abbreviations and Synonyms

Definitions

Lung disease due to inhalation of inorganic mineral dusts containing crystalline silicone dioxide (quartz)
Simple pneumoconiosis: Micronodules < 1 cm develop more than 10 years after long-term occupational exposure
Acute silicoproteinosis
- Rare fulminant respiratory complication of intense exposure to silica dust (typically sandblasting)
  - Appears within 6 months to 3 years after initial exposure
Caplan syndrome
- Seropositive rheumatoid arthritis associated with pneumoconiosis (coal, silica, or asbestos)

IMAGING FINDINGS

General Features

Best diagnostic clue: Centrilobular and subpleural nodules in upper lung zones
Patient position/location
- Rounded dusts like silica and coal predominantly affect dorsal aspect of upper lung zones
- Silica accumulates along lymphatics in centriacinar portion of lobule and lobule periphery
Size: Micronodules (< 10 mm in diameter)

CT Findings