Imaging of sarcoidosis of the airways and lung parenchyma and correlation with lung function

Imaging has a prominent role in the assessment of sarcoidosis diagnosis and outcome, which are extremely variable. Chest radiography staging helps predict the probability of spontaneous remission, and stage IV is associated with higher mortality. However, the reproducibility of reading is poor and changes in radiography and lung function are inconsistently correlated, which may be problematic for the monitoring of disease and treatment response. Chest computed tomography (CT) makes a great diagnostic contribution in difficult cases. Bilateral hilar lymphadenopathy with peri-lymphatic micronodular pattern is highly specific for sarcoidosis. CT is important for the investigation of pulmonary complications, including aspergilloma and pulmonary hypertension. CT improves the yield of bronchoscopy for obtaining a positive endobronchial or transbronchial biopsy. CT findings may also discriminate between active inflammation and irreversible fibrosis, with occasional influence on therapeutic decisions. Three CT patterns of fibrotic sarcoidosis are identified, with different functional profiles: predominant bronchial distortion is associated with obstruction; honeycombing is associated with restriction and lower diffusing capacity of the lung for carbon monoxide; whereas functional impairment is relatively minor with linear pattern. The clinical impact of correlations between CT severity scores and functional impairment is uncertain, except for its utility elucidating the mechanisms of airflow limitation, which include bronchial distortion, peribronchovascular thickening, air-trapping and bronchial compression by lymphadenopathy.