Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: PA and lateral views of the chest were provided . A large retrocardiac opacity containing an air - fluid level is compatible with a known hiatal hernia . There is a vague opacity at the left lung base which could represent pneumonia . Otherwise , the lungs appear clear . There may be a tiny left pleural effusion . No pneumothorax . Heart size appears stable . Mediastinal contour appears unchanged . The bony structures are intact .
    OUTPUT:
    
Large hiatal hernia . Subtle opacity in the left lung base may represent pneumonia or aspiration .