Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: The cardiomediastinal and hilar contours are within normal limits . As compared to prior chest radiograph from ___ , there is persistent mild left lung base opacity best seen on the lateral view , which appears slightly less conspicuous . There is no pneumothorax or pleural effusion .
    OUTPUT:
    
Persistent mild left lung base opacity is less conspicuous on today 's examination . These findings could relate to atelectasis , however persistent infection can not be excluded . Followup is recommended after treatment to document resolution .