Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: There are low lung volumes . The cardiomediastinal and hilar contours are stable . Retrocardiac opacity is again seen and may represent atelectasis or pneumonia or aspiration . There is a small left pleural effusion . No pneumothorax . Right upper mediastinal vascular calcification again seen .
    OUTPUT:
    
Retrocardiac opacity persists and may represent atelectasis or pneumonia . Small left pleural effusion . No significant change compared to ___ .