OBJECTIVE: The purpose of this study was to assess the diagnostic significance of CT patterns that cannot be classified according to current idiopathic pulmonary fibrosis (IPF) guidelines and of specific findings of the inconsistent with usual interstitial pneumonitis (UIP) pattern.
METHODS: Subjects with a multidisciplinary diagnosis of interstitial lung disease who had undergone surgical lung biopsy and chest CT within 1 year of each other were included in the study. The predominant distribution and pattern of disease were scored. Cases were classified as UIP, possible UIP, or inconsistent with UIP at chest CT according to 2011 IPF guidelines. Cases that could not be confidently categorized with current guidelines were annotated as indeterminate.
RESULTS: UIP, possible UIP, and inconsistent with UIP CT patterns were associated with pathologic UIP in 89.6%, 81.6%, and 60.0% of subjects. An indeterminate CT pattern (7.7% [20/259]) was associated with a UIP pathologic diagnosis in 55.0% of cases. This finding was not statistically different from the findings in the group with the inconsistent with UIP CT pattern (p = 0.677) but was different from the findings in the UIP (p < 0.001) and possible UIP (p = 0.031) groups. In regard to specific findings of the inconsistent with UIP CT category, ground-glass opacity, air-trapping, consolidation, and axial distribution were associated with a non-UIP pathologic diagnosis; however, there was no significant association with zonal distribution.
CONCLUSIONS: A substantial minority of cases cannot be confidently categorized according to current guidelines for IPF and differ diagnostically from the possible UIP and UIP CT categories. The term \"inconsistent with UIP\" is misleading and should be renamed.