Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: A left pigtail thoracostomy tube is unchanged in position , terminating at the left lung base . There is overall decreased retrocardiac density as compared to the ___ radiograph , likely reflective of interval drainage . No new consolidation or collection is detected . There is no pneumothorax . Mild left basilar atelectasis has improved .
    OUTPUT:
    
Interval decrease in density of the left retrocardiac opacity , likely secondary to drainage of known empyema . No new consolidation or collection . Improved left basilar atelectasis .