Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: There is subtle increased opacity in the retrocardiac region , not definitely visualized on the lateral view . Blunting of the right posterior costophrenic angle is new since yesterday 's exam in could be due to atelectasis although small effusion is possible . Elsewhere , the lungs are clear . Cardiomediastinal silhouette is stable . No acute osseous abnormalities .
    OUTPUT:
    
Subtle retrocardiac opacity not confirmed on the lateral view could be due to atelectasis . Infection is not entirely excluded , to be correlated clinically .