Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: The heart is mildly enlarged with a left ventricular configuration . The mediastinal and hilar contours appear within normal limits . There is a streaky left basilar opacity , which is concerning for pneumonia in the appropriate clinical setting . However , a similar appearance could probably be seen with atelectasis . Elsewhere , the lungs remain clear . There are no pleural effusions or pneumothorax . The bony structures are unremarkable .
    OUTPUT:
    
Left basilar retrocardiac opacity , which could be seen with pneumonia , although considerations would also include atelectasis .