Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: The cardiac silhouette size is mildly enlarged but unchanged . The mediastinal and hilar contours are normal . There is subtle hazy opacification within the left lung base , which may reflect an area of atelectasis or developing infection . No definite pleural effusion or pneumothorax is seen . Pulmonary vascularity is normal . There are no acute osseous findings .
    OUTPUT:
    
Subtle opacity within the left lung base , which could reflect an area of atelectasis though infection can not be excluded .