Ultrasound Detection of Gallstones

Ultrasound Characteristics

• Gallstones are typically identified as echogenic structures with distal posterior acoustic shadowing that are mobile with patient positioning, according to the American College of Emergency Physicians 1, 2
• Optimization of gain, frequency, and focal zone settings may be necessary to identify the Mercedes Benz sign or differentiate it from adjacent bowel gas, as recommended by the American College of Emergency Physicians 1, 2

Differential Diagnosis

• Pneumobilia can also produce increased echogenicity and comet-tailing caused by gas in the biliary tree, which must be distinguished from the Mercedes Benz sign, as noted by the American College of Emergency Physicians 3
• Emphysematous cholecystitis produces gas in the gallbladder wall and may create similar artifacts, according to the American College of Emergency Physicians 3

Clinical Considerations

• The presence of the Mercedes Benz sign or other findings consistent with cholelithiasis does not rule out other life-threatening causes of epigastric or right upper quadrant pain such as aortic aneurysm or myocardial infarction, as cautioned by the American College of Emergency Physicians 3