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Chronic Hypersensitivity Pneumonitis: Differentiation from Idiopathic Pulmonary Fibrosis and Nonspecific Interstitial Pneumonia by Using Thin-Section CT¹

¹ From the Departments of Radiology (C.I.S.S., N.L.M.) and Pathology (A.C.), Vancouver General Hospital, University of British Columbia, 3350-950 W 10th Ave, Vancouver, BC, Canada V5Z 4E3; Department of Radiology (D.A.L.), Division of Biostatistics (D.C.), and Department of Medicine (K.K.B.), National Jewish Medical and Research Center, Denver, Colo; Department of Preventive Medicine and Biometrics and Department of Physiology and Biophysics, University of Colorado at Denver and Health Sciences Center, Denver, Colo (D.C.); and Department of Radiology and Center for Imaging Science (K.S.L.) and Division of Pulmonary and Critical Care Medicine, Department of Medicine (M.P.C.), Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea. Received November 2, 2006; revision requested January 9, 2007; revision received January 18; accepted February 28; final version accepted April 17. Address correspondence to C.I.S.S. (e-mail: isabela.silva{at}vch.ca).

Purpose: To retrospectively assess the accuracy of thin-section computed tomography (CT) in distinguishing chronic hypersensitivity pneumonitis (HP) from idiopathic pulmonary fibrosis (IPF) and nonspecific interstitial pneumonia (NSIP), with histologic results as the reference standard.

Materials and Methods: This retrospective study was approved by the institutional research boards of the participating centers, and informed consent was waived. There was HIPAA compliance for all U.S. patients. The study included 66 patients (36 men, 30 women; mean age, 58.8 years ± 10.9 [standard deviation]) with proved chronic HP (n = 18), IPF (n = 23), or NSIP (n = 25) who underwent CT. Two independent readers assessed the CT images, made a first-choice diagnosis, and noted the degree of confidence in the diagnosis. A general linear model was used to identify CT features that independently differentiated chronic HP from IPF and NSIP. Weighted statistic was used to assess interobserver agreement.

Results: The CT features that best differentiated chronic HP were lobular areas with decreased attenuation and vascularity, centrilobular nodules, and absence of lower zone predominance of abnormalities (P .008). The features that best differentiated NSIP were relative subpleural sparing, absence of lobular areas with decreased attenuation, and lack of honeycombing (P .002). The features that best differentiated IPF were basal predominance of honeycombing, absence of relative subpleural sparing, and absence centrilobular nodules (P .004). A confident diagnosis was made in 70 (53%) of 132 readings. This diagnosis was correct in 66 (94%) of 70 readings. The accuracy for the entire cohort was 80%. Interobserver agreement for confident diagnosis was good to excellent ( = 0.77–0.96).

Conclusion: Characteristic CT features of chronic HP, IPF, and NSIP allow confident distinction between these entities in approximately 50% of patients.

© RSNA, 2008

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