Purpose: The aim of this study was to investigate the value of prone computed tomography (CT) in patients with underlying malignancies and posterior subpleural nodule(s) on a supine CT scan.
Method: A prospective study was performed on 26 patients who had an underlying malignancy and posterior subpleural nodule(s) on a chest CT scan. Helical CT scanning with a 3-mm collimation was done in both the supine and prone positions at an interval of 1-50 days (mean, 9 days). The size, shape, and location of the nodule(s) as well as the associated dependent ground-glass opacity on an initial CT scan and the change in the nodule(s) on follow-up supine and prone CT scans were analyzed.
Results: The nodules were single in 10 patients and multiple in 16. In 25 of 26 patients, the nodules were located in the lower lobes. Most had an oval shape, forming an obtuse angle with the adjacent pleura. The size ranged from 5 mm x 2 mm to 12 mm x 4 mm (mean, 7 mm x 3 mm). An associated dependent ground-glass opacity was found in 11 patients. At the follow-up examinations, the posterior subpleural nodules had disappeared in 10 patients on the supine scan and in 21 patients on the prone scan. The persistent nodules on the prone CT scan were granulomas in 2 patients and metastases in 3 patients.
Conclusion: Posterior subpleural nodules may be reversible, and the nodular atelectasis can be differentiated from true nodules without using invasive procedures by employing prone CT scanning.