The Siltzbach classification system defines five stages of sarcoidosis based on chest radiograph findings:
Stage 0 - No radiographic abnormality
Stage 1 - Lymphadenopathy
Stage 2 - Lymphadenopathy + pulmonary infiltrate
Stage 3 - Pulmonary infiltrate
Stage 4 - Pulmonary fibrosis
About 20% of patients with sarcoidosis will develop pulmonary fibrosis which indicates irreversible disease. Three main HRCT patterns of pulmonary fibrosis have been identified and linked to performance on pulmonary function tests:
1. Bronchial distortion in a primarily central distribution, associated with lower expiratory flow rates
2. Honeycombing in a peripheral and upper lobe distribution, associated with restriction and decreased diffusion capacity of carbon monoxide
3. Coarse, irregular linear opacities that radiate from the hila, associated with the least functional impairment.
Distinguishing between these patterns is important as it may predict treatment response to corticosteroids.
Abhesera M, Valeyre D, Grenier P, et al. Sarcoidosis with pulmonary fibrosis: CT pattern and correlation with pulmonary function. AJR Am J Roentgenol 2000;174(6):1751-1757.
Criado E, Sanchez M, Ramirez J, et al. Pulmonary sarcoidosis: typical and atypical manifestations at high resolution CT with pathologic correlation. Radiographics 2010;30:1567-1586.