Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: The heart size is normal . The hilar and mediastinal contours are unremarkable . There is opacification at the lung bases likely secondary to atelectasis . There is no pleural effusion . Scant calcification of the aortic knob is again noted . There is no pneumothorax . The visualized osseous structures demonstrate marked degenerative changes in the thoracic spine .
    OUTPUT:
    
Bibasilar opacities likely reflect atelectasis , but infectious process can not be excluded .