Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: The cardiac , mediastinal and hilar contours appear unchanged . Mild subpleural scarring is unchanged at each lung apex . Although there is no pleural effusion on the right , there is a new small pleural effusion on the left since four days earlier . Patchy associated opacity in the retrocardiac area is streaky , possibly atelectasis .
    OUTPUT:
    
New small pleural effusion . Possibly increasing opacification of the left lung base reflects early developing infection but does not represent a definite infectious source since atelectasis and pleural effusion could yield a similar appearance .