<b>Background: </b> Ever since Katzenstein and Fiorelli introduced the term nonspecific interstitial pneumonia (NSIP) to denote those cases of interstitial pneumonia that cannot be categorized as any of the other types of idiopathic interstitial pneumonias (IIP), there has been continuing debate on whether it is a real clinical entity or not. The American Thoracic Society/European Respiratory Symposium task group tried to identify idiopathic NSIP as a separate disease and exclude it from the category of IIP. However, it appears that the clinical presentation of NSIP and usual interstitial pneumonia (UIP) are the same. <b> Objective :</b> To show that the radiologic features of NSIP and UIP should be relied upon, instead of clinical presentation and pathologic findings, to differentiate between the two. <b> Materials and Methods:</b> Consecutive patients who had received a diagnosis of either NSIP or UIP on the basis of open lung biopsy between January 2001 and December 2007 were identified for inclusion in this retrospective review. The study included 61 subjects: 32 men and 29 women with a mean age of 59.39 ± 14.5 years. Chest computed tomography images of all the cases were collected for a review. High resolution computed tomography (HRCT) and all pathologic specimens were also evaluated. A weighted kappa coefficient was used to evaluate whether radiology can be used instead of biopsy for the diagnosis of NSIP and UIP. Comparison of the mean ages and the time intervals (i.e., interval between symptom onset and the time of diagnosis) in the UIP and NSIP groups was done using the Mann-Whitney U test. Association between gender and biopsy result was evaluated by the Fisher exact test. Data were evaluated using SPSS, v.13. <b> Results :</b> Sixty-one patients were included in this study, 32 were male and 29 were female. On the basis of biopsy findings, 50 (82%) patients had UIP and 11 (18%) had NSIP. Thirty (60%) of the 50 patients who had UIP were male and 20 (40%) were female; 2 (18.2%) of the 11 patients who suffered from NSIP were male and 9 (81.8%) were female. Based on HRCT findings, 36 (60%) patients were diagnosed to have UIP and 24 (40%) were diagnosed with NSIP. When diagnosis was based on biopsy findings, the time interval in the UIP group was 13.59 ± 8.29 months and in the NSIP group it was 7.90 ± 4.18 months. When diagnosed on the basis of HRCT findings, the time interval in the UIP group was 14.22 ± 8.94 months and in the NSIP group it was 10.54 ± 5.78 months. When diagnosis was on the basis of biopsy, the mean age in the UIP group was 61.30 ± 14.18 years and in the NSIP group it was 50.73 ± 13.14 years. <b> Conclusion :</b> HRCT can be used instead of invasive methods like lung biopsy to differentiate between UIP and NSIP
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