Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: The heart size is normal . Hilar and mediastinal contours are unremarkable . Lung volumes are low . There is slight opacification at the left lung base . No pleural effusions are seen . There are no pneumothoraces . Note is made of slight left pleural thickening .
    OUTPUT:
    
Left lower lobe opacification likely secondary to atelectasis ; however , infection can not be excluded .