Additional computed tomography scans in the prone position to distinguish early interstitial lung disease from dependent density on helical computed tomography screening patient characteristics

Background: The purpose of this study was to evaluate the benefit of additional prone CT scanning to helical CT screening to detect early interstitial lung disease (ILD). Methods: Helical CT screening was performed as an optional test in 1098 subjects during their annual health examination. Subjects with parenchymal abnormalities in the posterior subpleural aspect of the lung were advised to receive additional CT scans in the prone position. The CT images were assessed independently by both a radiologist and a chest specialist without reference to clinical data. Results: Ninety-three subjects (8%) had parenchymal abnormalities in the posterior subpleural aspect of the lung and 75 subjects (7%) received additional CT scans. These revealed 72 dependent densities and three early ILD (0.3%). By multivariate analysis, subjects aged over 70 years, with obesity (BMI >= 25) and currently smoking (pack years >= 20) had a tendency to have dependent density on helical CT, the predominant distribution of which was in the middle lung fields. Conclusions: Additional CT scans were performed in 7% of subjects after abnormal CT screening and three early ILD were detected. Therefore, we recommend that additional CT scans in prone position be performed to detect early ILD after abnormal helical CT screening.