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Vignette: A 68 yr old male retired cement factory worker presented with progressive exertional dyspnea and clubbing. PA and Lateral plain films were obtained.

Image Findings:
Multiple diffuse opacities can be seen in the lower lung fields. Lateral view shows diffuse plaques in the lung parenchyma as well as the pleura. Heart and diaphragmatic contours are poorly defined. Given the patient’s occupational exposure to asbestosis, these findings are most consistent with a diagnosis of asbestosis.

Asbestosis:
Asbestosis is a diffuse parenchymal lung disease caused by the formation of fibrous plaques in response to exposure to asbestos dust. Though environmental exposure to asbestos is now limited by regulations, there is a 10-20 year latency from exposure to symptoms so patients continue to present with asbestos-related diseases.

The severity of asbestosis seems to be proportional to the level of exposure, and is usually seen in patients with a 10+ year history of occupational exposure. Asbestos fibers in the lungs induce an inflammatory response that leads to fibrogenesis around the fibers. The process occurs bilaterally in the lower lobes, although in advanced disease, the middle and even upper lobes may be involved.

Clinical symptoms resemble those of other interstitial lung diseases and include:
• Progressive dyspnea
• Inspiritory crackles
• Clubbing
• Cyanosis (rare)
• Reduced diffusion capacity and compliance on pulmonary function tests

Radiographic Findings:
On plain radiograph:
• Shaggy heart sign
• “Ground-glass” opacification
• Small nodular opacities
• Ill-defined diaphragmatic contours
• Honeycombing (more severe cases)
• Pleural thickening
• Calcified pleural plaques

CT is more sensitive for detecting asbestosis and is useful in early diagnosis.
• Subpleural curvilinear opacities
• Parenchymal bands projecting in from pleura
• Ground-glass opacification
• Subpleural nodular opacities
• Thickening of interlobular septa
• Pleural plaques

Differential Diagnosis
Diagnosis of asbestosis is based on occupational exposure history and radiographic findings of diffuse lung disease. Pleural involvement is common in asbestosis but rare in other diffuse lung diseases. The differential diagnosis includes:

• Interstitial pneumonitis
• Idiopathic pulmonary fibrosis
• Connective tissue disease (sarcoidosis, systemic lupus erythematosis, rheumatoid arthritis)
• Other pneumoconiosis (eg silicosis)
• Pleurodesis
• Multifocal malignancy or calcified metastatic disease

References
Roach HD, et al. Asbestos: when the dust settles an imaging review of asbestos-related disease. Radiographics. 2002 Oct;22 Spec No:S167-84.

Speizer FE & Balmes JR. “Chapter 250. Environmental Lung Disease” (Part 10, Section 2). Fauci AS et al: Harrison’s Principles of Internal Medicine, 17e.