Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: There has been slight decrease in size of a very large left pleural effusion since the ___ examination , with improved aeration of the left upper zone . The right lung remains clear . The mediastinal contour is unchanged . There is no pneumothorax .
    OUTPUT:
    
Interval decrease in size of a very large left pleural effusion with slightly improved left aeration . No pneumothorax .