Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: The lungs are normally expanded . There is a faint left retrocardiac opacity . Heart size is normal . The mediastinal contours are normal . There is no pleural effusion or pneumothorax .
    OUTPUT:
    
Faint left retrocardiac opacity is nonspecific and could reflect atelectasis , however pneumonia or aspiration can not be excluded . A lateral projection may be helpful for confirmation .