Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Compared to the prior chest radiograph ___ there is no significant change in a small left retrocardiac opacity which most likely represents atelectasis . No new opacity , pleural effusion and pneumothorax . Mild cardiomegaly is stable . The mediastinal silhouette is stable .
    OUTPUT:
    
Left lower lobe atelectasis . Otherwise , clear lungs .