Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: The size of the left pleural effusion has decreased since ___ , now small . There is associated atelectasis , however an underlying pneumonia at the left base can not be entirely excluded . Otherwise , the lungs are clear . No pulmonary edema . Normal appearance of the cardiomediastinal silhouette . No pneumothorax . Cervical fixation hardware is visualized .
    OUTPUT:
    
Interval decrease in the size of the left pleural effusion since ___ , now small . An underlying pneumonia can not be entirely excluded .