Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Frontal and lateral views of the chest . Heart size is top normal and mediastinal contours are stable . Small left lung base opacity is most likely atelectasis , though infection is not entirely excluded . No pleural effusion or pneumothorax .
    OUTPUT:
    
Small left base opacity is most likely atelectasis , though infection can not be excluded in the appropriate clinical setting .