Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Cardiac size is mildly enlarged , likely exaggerated by the AP projection . There is no pleural effusion . Lung volumes are low . A retrocardiac opacity is noted and also seen on the lateral view which may represent a hiatal hernia , though more pronounced when compared with the prior exam . Difficult to exclude a subjacent pneumonia / mass . Bony structures appear intact .
    OUTPUT:
    
Retrocardiac opacity which may represent a hiatal hernia , though somewhat increased as compared with prior exam , raising potential for subjacent pneumonia / mass .