Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: The heart is mildly enlarged . The mediastinal and hilar contours appear within normal limits . Blunting of the left costophrenic sulcus and flattening of the hemidiaphragmatic contour suggest a small pleural effusion . Retrocardiac opacity is nonspecific . On the prior study , there was a known mass that may partly account for this appearance , but associated atelectasis or superimposed pneumonia are not excluded .
    OUTPUT:
    
Stable appearance of the chest . Standard PA and lateral radiographs may be helpful in short - term follow - up if pulmonary symptoms are present and were to persist .