Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: AP upright and lateral views of the chest are provided . There is a posteriorly pleural - based opacity in the right lower lung which is stable from multiple prior exams , likely reflecting known loculated pleural effusion and rounded atelectasis . There is slight rightward shift of midline structures likely due to the chronic atelectasis within the right lung base . Otherwise , the lungs are clear . Heart size is within normal limits . Mediastinal contour appears normal , though aorta is slightly unfolded . The bony structures are intact .
    OUTPUT:
    
Stable chronic opacity at the right lung base likely reflecting a combination of loculated effusion and rounded atelectasis . No significant interval changes .