Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: AP upright and lateral views of the chest were provided . Lungs appear clear , though volumes are low . There is a retrocardiac rounded density which could represent a hiatal hernia , though this is unconfirmed . The cardiomediastinal silhouette is stable with top normal heart size . Bony structures are intact .
    OUTPUT:
    
Rounded retrocardiac opacity , may represent a hiatal hernia . Top normal heart size .