Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: AP upright and lateral views of the chest provided . Large retrocardiac opacity containing an air - fluid level is consistent with large hiatal hernia as seen on prior . The lower lungs are poorly assessed given large hiatal hernia . The mid upper lungs appear well aerated . The heart size can not be assessed . No left - sided effusion . Difficult to exclude a small right effusion . Bony structures are intact .
    OUTPUT:
    
Large hiatal hernia . Possible small right pleural effusion .