Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Retrocardiac opacity seen at the left lung base , is largely unchanged from the prior examination of ___ . This could represent atelectasis or infection . The cardiomediastinal silhouette and hilar contours are normal . The pleural surfaces are normal without effusion or pneumothorax .
    OUTPUT:
    
Left lung base opacity , not significantly changed from the prior exam which could represent atelectasis or infection . Consider PA and lateral of the chest for further evaluation .