Comparison of CT images obtained on both the supine and the prone scan in 23 patients of interstitial pneumonitis

CT images obtained on both the supine scan (S-CT) and the prone scan (P-CT) were compared in 23 patients who were suspected to have interstitial pneumonitis (IP) based on abnormal lung attenuations in the posterobasal portions. In 5 of 23 patients (22%), abnormal lung attenuations were remarkably diminished on P-CT. It was suggested that abnormal lung attenuation observed on S-CT by these patients were due to the effect of gravity on pulmonary vascularity and dravity-dependent atelectasis in the supine potion. From these results, it was suggested that IP was overdiagnosed if decided only on the basis of S-CT images. In these cases, invasive procedure, such as video-assisted thoracic surgery (VATS), may be unnecessary, and if carried out, pathologic-CT correlation may be confusing. Therefrom the patients with abnormal shadows in posterobasal portions on plain radiography, we recommend to obtain P-CT initially instead of S-CT. (author)