Objective: The purpose of this article is to illustrate the spectrum of pathologic and high-resolution CT features of hypersensitivity pneumonitis (HP).
Conclusion: High-resolution CT plays an important role in the diagnosis of HP. A confident diagnosis of subacute HP is based on the presence of ground-glass opacities, poorly defined centrilobular nodules, and mosaic attenuation on inspiratory images and of air trapping on expiratory CT images. Chronic HP is characterized on high-resolution CT by the presence of reticulation due to fibrosis superimposed on findings of subacute HP. Histologically, subacute HP is characterized by the presence of cellular bronchiolitis, noncaseating granulomas, and bronchiolocentric lymphocytic interstitial pneumonitis. Areas of organizing pneumonia also may be seen. The high-resolution CT and pathologic features of chronic HP frequently overlap with those of nonspecific interstitial pneumonia and usual interstitial pneumonia. Awareness of the various manifestations of HP is important for early diagnosis and management.