Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Mild cardiomegaly has slightly increased in size compared to the prior exam from ___ . The hilar and mediastinal contours are unremarkable . Subtle increase in retrocardiac opacity is likely secondary to atelectasis . There is no large pleural effusion or pneumothorax . The visualized osseous structures are unremarkable .
    OUTPUT:
    
Subtle increase in opacity at the retrocardiac region is likely secondary to atelectasis ; however , an infectious process can not be entirely excluded .