Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Cardiomediastinal contours are within normal limits . Lungs are remarkable for biapical scarring and a nonspecific patchy opacity in the left retrocardiac region , most likely representing patchy atelectasis . Differential diagnosis includes focal aspiration and an early focus of pneumonia .
    OUTPUT:
    
Patchy left retrocardiac opacity as detailed above .