Radiology: Volume 268: Number 2-August 2013 n radiology.rsna.org 563 Purpose:To determine the prevalence of interstitial lung abnormalities (ILAs) at initial computed tomography (CT) examination and the rate of progression of ILAs on 2-year follow-up CT images in a National Lung Screening Trial population studied at a single site. Materials and Methods:The study was approved by the institutional review board and informed consent was obtained from all participants. Image review for this study was HIPAA compliant. We reviewed the CT images of 884 cigarette smokers who underwent low-dose CT at a single site in the National Lung Screening Trial. CT findings were categorized as having no evidence of ILA, equivocal for ILA, or ILA. We categorized the type of ILA as nonfibrotic (ground-glass opacity, consolidation, mosaic attenuation), or fibrotic (ground glass with reticular pattern, reticular pattern, honeycombing). We evaluated the temporal change of the CT findings (no change, improvement, or progression) of ILA at 2-year follow-up. A x 2 with Fisher exact test or unpaired t test was used to determine whether smoking parameters were associated with progression of ILA at 2-year follow-up CT. Results:The prevalence of ILA was 9.7% (86 of 884 participants; 95% confidence interval: 7.9%, 11.9%), with a further 11.5% (102 of 884 participants) who had findings equivocal for ILA. The pattern was fibrotic in 19 (2.1%), nonfibrotic in 52 (5.9%), and mixed fibrotic and nonfibrotic in 15 (1.7%) of the 86 participants with ILA. The percentage of current smokers (P = .001) and mean number of cigarette pack-years (P = .001) were significantly higher in those with ILA than those without. At 2-year follow-up of those with ILA (n = 79), findings of nonfibrotic ILA improved in 49% of cases and progressed in 11%. Fibrotic ILA improved in 0% and progressed in 37% of cases. Conclusion:ILA is common in cigarette smokers. Nonfibrotic ILA improved in about 50% of cases, and fibrotic ILA progressed in about 37%.q RSNA, 2013 interstitial lung abnormalities in a cT lung cancer screening Population: Prevalence and Progression Rate

The role of high-resolution computed tomography in the diagnosis of interstitial lung disease is increasing as our understanding of its diagnostic accuracy improves. The characteristic findings on high-resolution computed tomography of usual interstitial pneumonia (UIP) are reticular abnormality and honeycombing with basal predominance. Honeycombing is a strong predictor of UIP and also is an important predictor of mortality. Because UIP carries the most adverse prognosis among the subtypes of idiopathic interstitial pneumonia, it is important to be able to differentiate this entity from nonspecific interstitial pneumonia and desquamative interstitial pneumonia from UIP, because these patients may show similar clinical presentations. A confident computed tomography diagnosis of UIP, in association with typical clinical features, will allow the clinician to avoid an unnecessary surgical biopsy.

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Compared with patients with CVD, those patients with an idiopathic fibrosing interstitial pneumonia showed a higher prevalence of a UIP pattern and lower prevalence of an NSIP pattern as determined by CT. Identification of coexisting extrapulmonary abnormalities on CT can support a diagnosis of CVD.

The extent of honeycombing at baseline and its progression on follow-up CT are important determinants of rate of survival in patients with fibrosing interstitial pneumonia.