Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Endotracheal tube and nasogastric tube are in standard position , and cardiomediastinal contours are within normal limits for technique . A subtle area of opacity has developed in the left retrocardiac region , but lungs are otherwise clear , and no acute pleural abnormalities were detected .
    OUTPUT:
    
New left retrocardiac opacity , possibly due to aspiration given history of recent suspected aspiration event . Atelectasis and infectious pneumonia could produce a similar radiographic appearance .