Hypersensitivity pneumonitis: Correlation of individual CT patterns with functional abnormalities

PURPOSE: To correlate the pattern and extent of abnormalities on thin-section computed tomographic (CT) scans with pulmonary function test results in subacute and chronic hypersensitivity pneumonitis. MATERIALS AND METHODS: Thin-section scans (1-3-mm collimation) obtained in 22 patients were assessed for pattern of abnormality and extent of disease. CT scores were correlated with functional parameters by using Spearman rank correlation and forward stepwise regression analysis. RESULTS: The most common CT patterns were decreased attenuation and mosaic perfusion (n = 19), ground-glass opacification (n = 18), small nodules (n = 12), and a reticular pattern (n = 8). Areas of decreased attenuation correlated with severity of air trapping indicated by residual volume (r = .58, P < .01), whereas ground-glass opacification and reticulation correlated independently with restrictive lung function. CONCLUSION: Areas of decreased attenuation and mosaic perfusion are an important ancillary CT finding in hypersensitivity pneumonitis, and obstructive functional abnormalities indicate that this phenomenon is caused by bronchiolitis.