Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Bronchovascular markings are exaggerated by low lung volumes . There is a retrocardiac opacity that is new from the prior study in ___ and may represent atelectasis , although infection should be considered in the appropriate clinical setting . No pleural effusions or pneumothorax . Cardiomediastinal silhouette is within normal limits . No acute osseous abnormalities are identified .
    OUTPUT:
    
Left retrocardiac opacity new since ___ , which may represent atelectasis but pneumonia should be considered in the appropriate clinical setting .