Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Lung volumes are low . This accentuates the size of the cardiac silhouette which is top normal . The mediastinal and hilar contours are unremarkable . There is crowding of the bronchovascular structures , but no overt pulmonary edema is demonstrated . There is a possible small left pleural effusion . Patchy opacity in the retrocardiac region is likely atelectasis given the low lung volumes , but an early pneumonia is not completely excluded . There is no pneumothorax . No acute osseous abnormalities seen .
    OUTPUT:
    
Low lung volumes . Minimal patchy retrocardiac opacity may reflect atelectasis though infection can not be completely excluded . Probable trace left pleural effusion .