Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: The cardiac , mediastinal and hilar contours are normal . The pulmonary vasculature is normal . Linear opacity within the left lung base may reflect an area of scarring or atelectasis . There is blunting of the left costophrenic sulcus which could reflect a trace pleural effusion . Lungs are hyperinflated . No pneumothorax is seen . There are multilevel degenerative changes in the thoracic spine .
    OUTPUT:
    
Linear opacity in the left lung base may reflect subsegmental atelectasis or scarring . Trace left pleural effusion .