Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Lung volumes are low . Heart size is top normal . Mediastinal and hilar contours are unchanged . Patchy retrocardiac opacity appear similar compared to the previous study , potentially atelectasis though infection can not be completely excluded . No pleural effusion or pneumothorax is seen . Bronchovascular structures are crowded due to low lung volumes without overt pulmonary edema . No acute osseous abnormalities seen .
    OUTPUT:
    
Retrocardiac patchy opacity likely reflects atelectasis , though infection can not be completely excluded .