Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Previously seen retrocardiac opacification is increased in density , possibly representing worsening atelectasis . Lung volumes are reduced compared to the prior study . Cardiomediastinal silhouette is accentuated as a result . No large pleural effusion or pneumothorax .
    OUTPUT:
    
Interval increase in density of the retrocardiac opacification may represent atelectasis .