Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Patchy left base retrocardiac opacity most likely represents atelectasis . No pleural effusion or pneumothorax is seen . The cardiac silhouette is mildly enlarged . Mediastinal and hilar contours are unremarkable .
    OUTPUT:
    
Likely left base atelectasis . Mild cardiomegaly .