Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Compared with the prior chest radiograph , increased opacification in the retrocardiac region is worrisome for developing left lower lobe pneumonia . No pleural effusion or pneumothorax . Cardiomediastinal silhouette is unchanged .
    OUTPUT:
    
Increased retrocardiac opacification , concerning for developing left lower lobe pneumonia .