Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: The lungs are well expanded . There is a subtle retrocardiac opacity , which could represent atelectasis but would be concerning for pneumonia or aspiration in the correct clinical setting . There is a possible small left pleural effusion . There is no right pleural effusion or pneumothorax . The cardiomediastinal silhouette is unremarkable .
    OUTPUT:
    
Probable retrocardiac opacity , which could represent atelectasis but would be concerning for pneumonia or aspiration in the correct clinical setting . Possible small left pleural effusion .