Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: As compared to prior chest radiograph from ___ , a left - sided pigtail catheter has apparently slightly changed in position . Left - sided pleural effusion demonstrates interval improvement with near complete resolution . There has been interval increase of a left perihilar opacity , for which differential diagnosis includes post-obstructive pneumonia . There is atelectasis of the left lung base . The right lung is hyperinflated and clear .
    OUTPUT:
    
1 . Near complete resolution of left - sided pleural effusion . 2 . Increasing left perihilar opacity for which differential diagnosis includes post-obstructive pneumonia .