Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: The lungs are moderately well inflated with subtle retrocardiac opacity . No pulmonary edema . No pleural effusion or pneumothorax . The heart is top - normal in size . Mediastinal contour and hila are unremarkable .
    OUTPUT:
    
Subtle left base opacity most likely represents atelectasis however early pneumonia can not be excluded in the appropriate clinical setting .