Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: PA and lateral views of the chest provided demonstrate a large retrocardiac opacity with an air - fluid level compatible with a large hiatal hernia , not significantly changed from prior . The lungs are clear without focal consolidation , effusion or pneumothorax . There is linear density at the left lung base which could represent a small amount of scarring or atelectasis . Heart size appears grossly stable . The mediastinal contour is unremarkable . No pneumothorax is seen . Bony structures are intact .
    OUTPUT:
    
No acute findings in the chest . Large hiatal hernia re-demonstrated .