Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: The cardiac silhouette size is mildly enlarged . The aorta demonstrates aortic knob calcifications . Mediastinal and hilar contours are otherwise unremarkable . Pulmonary vascularity is normal . Streaky opacity in the retrocardiac region likely reflects atelectasis . No pleural effusion or pneumothorax is identified . No acute osseous abnormality is present .
    OUTPUT:
    
Mild retrocardiac atelectasis .