Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: The small left apical pneumothorax has decreased in size . There has been interval improvement in mediastinal widening , with improved aeration bilaterally . There is a persistent opacity at the left lung base , likely representing a combination of pleural effusion and atelectasis , though superimposed pneumonia can not be ruled out . There has been interval removal of the right IJ introduction sheath . There is no pulmonary edema .
    OUTPUT:
    
1 . Interval decrease in size of a small left apical pneumothorax . 2 . Persistent left base opacity , likely a combination of pleural effusion and atelectasis , superimposed pneumonia can not be ruled out .