Mercedes Benz Sign on Ultrasound
The Mercedes Benz sign indicates gas within fissures or clefts of gallstones, representing a specific radiographic finding of cholelithiasis that is characteristic and diagnostic for the presence of calculi. 1, 2
What the Sign Represents
The Mercedes Benz sign appears as gas trapped within the internal fissures of gallstones, creating a three-pronged appearance resembling the Mercedes Benz logo 1, 2
This finding is most commonly seen on CT imaging rather than ultrasound, though it can occasionally be identified sonographically 1
The gas is believed to be released from solution due to negative pressure within cholesterol stones undergoing internal fissuring related to their crystalline structure 2
Clinical Context and Associations
Most reported cases with this sign have been associated with biliary colic or cholecystitis 2
When present, this finding is characteristic and definitively indicates the presence of one or more gallstones 2
This is a relatively uncommon finding, but when identified, it provides high specificity for cholelithiasis 2
Ultrasound Detection Considerations
On ultrasound, gallstones are typically identified as echogenic structures with distal posterior acoustic shadowing that are mobile with patient positioning 3
Optimization of gain, frequency, and focal zone settings may be necessary to identify the Mercedes Benz sign or differentiate it from adjacent bowel gas 3
The sign may produce comet-tail artifact due to gas, which can be confused with cholesterol stones or pneumobilia 3
Important Differential Considerations
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 3
Emphysematous cholecystitis produces gas in the gallbladder wall and may create similar artifacts 3
The Mercedes Benz sign specifically refers to gas within the stone itself, not in surrounding structures 1, 2
Clinical Pitfall
- 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 3