Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: The heart size is normal . The aorta remains tortuous ; however , otherwise , the hilar and mediastinal contours are unremarkable . There is a left lower lobe opacity which is non-specific , and may be secondary to atelectasis or infection . No pleural effusion or pneumothorax is identified . No acute osseous abnormalities are identified . Again seen are multilevel degenerative changes in the thoracic spine .
    OUTPUT:
    
Left lower lobe opacity , secondary to either atelectasis or infection .