Chronic hypersensitivity pneumonitis and pulmonary sarcoidosis: differentiation from usual interstitial pneumonia using high-resolution computed tomography.

The distinction of chronic hypersensitivity pneumonitis (HP) or advanced-stage sarcoidosis from idiopathic pulmonary fibrosis or usual interstitial pneumonia is important because each disease is managed differently and may have a different prognosis. The analyses of pattern and distribution of lung parenchymal abnormalities on high-resolution computed tomography scans help differentiate among the 3 diseases. In chronic HP, the presence of lobular areas of decreased attenuation and centrilobular small nodules and the absence of lower lung zone predominance are characteristically observed. In advanced-stage sarcoidosis, patchy areas of reticulation, traction bronchiectasis, architectural distortion, honeycomblike cysts, bullae, and paracicatricial emphysema are observed in the upper and middle lung zones. Lung bases are usually spared. In idiopathic pulmonary fibrosis or usual interstitial pneumonia, however, the presence of honeycombing with lower lung zone predominance and the absence of centrilobular small nodules are important findings that allow us to differentiate the disease from chronic HP or advanced-stage sarcoidosis. In the 3 diseases, most important prognosis-predicting factor is the extent of fibrotic score (the extent of honeycombing and reticulation) calculated on high-resolution computed tomography scans or fibrosis estimated on chest radiographs.