Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: The heart size is normal . The hilar and mediastinal contours are normal . Atherosclerotic calcification of the aorta is noted . Linear opacity in the left mid lung field likely reflects an area of scarring or subsegmental atelectasis . Remainder of the lungs are clear without evidence of focal consolidations concerning for pneumonia . Lungs are hyperinflated . There is no pleural effusion or pneumothorax . There is a old healed rib fracture involving the left posterior 4th rib .
    OUTPUT:
    
Old healed rib fracture involving the left posterior 4th rib . No acute intrathoracic abnormalities identified .