Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: The lung volumes are stable . A retrocardiac opacity does not the hemidiaphragm silhouettes . There is however a lower left lung opacity partially obscuring the left heart border . The cardiomediastinal hilar contours are normal . The pleural surfaces are normal . Stable degenerative changes of thoracic spine .
    OUTPUT:
    
Left lower lung opacity , less likely a retrocardiac opacity , could represent atelectatic changes or in the appropriate clinical setting may represent a consolidation suggestive of pneumonia .