Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: The cardiac , mediastinal and hilar contours appear unchanged . There is a persistent streaky retrocardiac opacity which is nonspecific in character but given chronicity is probably due to scarring or atelectasis . Elsewhere the lungs appear clear within the limitations of technique . There is no pleural effusion or pneumothorax .
    OUTPUT:
    
Persistent retrocardiac opacity , but unchanged , so no definite acute process .