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CT Often Distinguishes Chronic HP From IPF and NSIP

June 6, 2008
Written by: , Filed in: Chest Radiology
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A recent study was conducted to evaluate the accuracy of CT in distinguishing between chronic hypersensitivity pneumonitis (HP), idiopathic pulmonary fibrosis (IPF), and nonspecific interstitial pneumonia (NSIP).

The study has concluded that CT imaging can be used to distinguish chronic hypersensitivity pneumonitis, idiopathic pulmonary fibrosis, and nonspecific interstitial pneumonia.

Participants
In this retrospective analysis, 18 patients with chronic HP, 23 patients with IPF, and 25 patients with NSIP were included. All patients had their diagnosis proven histopathologically with a surgical lung biopsy, and all patients had a thin-section CT of the lungs.

Methodology
CT scans were performed with 1.0- to 1.5-mm collimation at 10- or 20-mm intervals or volumetrically with 1.00- to 1.25-mm reconstruction.

Additional expiratory images were obtained in slightly <50% of the patients. CTs were independently reviewed by 2 thoracic radiologists who were blinded to the diagnosis but knew that each patient had chronic HP, IPF, or NSIP. The CTs were evaluated for the presence of reticulation (linearly oriented irregular opacities), ground-glass opacity, consolidation, centrilobular nodules, cysts, honeycombing, traction bronchiectasis/bronchiolectasis, and lobular areas of decreased attenuation associated with diminished vascularity. The anatomic distribution of pulmonary parenchymal abnormalities was also characterized. Each radiologist made a diagnosis (HP, IPF, or NSIP) and also graded their degree of confidence (high or confident and low or probable). An "indeterminate" diagnosis could also be made. [text_ad] Results Interobserver agreement was good to excellent between the 2 readers (kappa = 0.68 to 1.00). A confident diagnosis was made in 70 (53%) of 132 readings. This confident diagnosis was correct in 66 (94%) of the 70 patients. Chronic HP was best differentiated from the other diagnoses by the presence of lobular areas of decreased attenuation associated with diminished vascularity, centrilobular nodules, and the lack of lower lung zone predominance of abnormalities (P <=0.008). IPF was best differentiated from the other diagnoses by the presence of a basal predominance of honeycombing, absence of relative subpleural sparing of abnormality, and lack of centrilobular nodules (P <=0.004). NSIP was best differentiated from the other diagnoses by the presence of relative subpleural sparing of abnormality, lack of honeycombing, and absence of lobular areas of decreased attenuation associated with diminished vascularity (P <=0.002). Conclusions
In approximately 50% of patients, CT findings can be used to distinguish between chronic HP, IPF, and NSIP.

Reviewer’s Comments
The authors have demonstrated that although there is overlap between the findings of these 3 diseases, CT can often discriminate between them.

Author: Vineet R. Jain, MD

Reference:
Silva CIS, Muller NL, et al. Chronic Hypersensitivity Pneumonitis: Differentiation From Idiopathic Pulmonary Fibrosis and Nonspecific Interstitial Pneumonia by Using Thin-Section CT. Radiology 2008; 246 (January): 288-297

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