Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: There is faint retrocardiac opacity focally silhouetting the hemidiaphragm . Elsewhere , the lungs are grossly clear . The cardiac silhouette is top - normal . No acute osseous abnormalities . Increased sclerosis at the bilateral humeral heads is likely due to avascular necrosis . H - shaped vertebral bodies are again noted . Surgical clips in the right upper quadrant suggest prior cholecystectomy .
    OUTPUT:
    
Very slight retrocardiac opacity which is potentially atelectasis . If persistent clinical concern , consider PA and lateral for further characterization .