Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: The heart size , mediastinal , and hilar contours are normal . Faint left basilar opacity is thought to be atelectasis . No pleural effusions , or pneumothorax .
    OUTPUT:
    
Faint left basilar opacity is thought to represent atelectasis . However , superimposed pneumonia is difficult to exclude in the correct clinical setting .