Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Compared to the prior study there has been slight improvement in opacification of the right lower lung related to combination of effusion and atelectasis . Stable heart size with normal mediastinal and hilar contours . The left lung is clear .
    OUTPUT:
    
Slight improvement in right lower lung opacity likely due to a combination of pleural effusion and atelectasis ; however , superimposed pneumonia can not be excluded .