Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Chest PA and lateral radiographs demonstrate unremarkable mediastinal and hilar contours . Cardiac contour is top normal . Low lung volumes noted bilaterally with vascular crowding and bibasilar atelectasis . Faint retrocardiac opacity noted on frontal view likely represents atelectasis or scarring , though can not entirely exclude infection in the appropriate clinical setting .
    OUTPUT:
    
Top normal cardiac silhouette with faint retrocardiac opacity , likely atelectasis given low lung volumes , can not entirely exclude pneumonia , but unlikely given the lack of evidence change .