Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: There is mild enlargement of cardiac silhouette . The mediastinal contours are unchanged . There is mild pulmonary edema . Small left pleural effusion is noted , decreased in size compared to the previous exam . Retrocardiac opacity likely reflects compressive atelectasis . No pneumothorax is identified . There are multilevel degenerative changes in the thoracic spine as well as involving the acromioclavicular joints .
    OUTPUT:
    
Mild pulmonary edema and small left pleural effusion , the latter of which is improved compared to the prior study . Retrocardiac opacity likely reflects compressive atelectasis but infection is not excluded .