CASE 7689 Published on 31.08.2009

The “Mercedes-Benz sign”


Abdominal imaging

Case Type

Clinical Cases


Alves N, Sousa M, Herédia V.


66 years, male

Clinical History
A 66 year old man underwent CT following blunt trauma to the chest and abdomen.
Imaging Findings
A 66 year old Caucasian male suffered a motor vehicle accident and was brought to the emergency department. A CT scan of the thorax and abdomen was obtained, revealing linear lucency of the sternal body, corresponding to a fractured sternum.
Three separate lucencies with gas density were observed in the lumen of the gallbladder. These were surrounded by hyperdense round rims, suggesting gallstones containing gas.
The “Mercedes-Benz sign” consists in radio-transparent fissures in biliary calculi.
The fissures are radial, usually wider centrally, or star-shaped, resembling the Mercedes-Benz logo, though they may present with a peripheral widening.
More often one can identify three radial fissures, although reports have described one to five. They are usually of the same length, though not always equidistant to each other. The fissures generally course perpendicular to the middle point of each facet, along the central two-thirds of the gallstone, not extending to the surface of the calculus.

The presence of gas within gallstones is known for over 200 years, but the meaning of this finding has been debated. In imaging terms, the identification of a tri-radiate transparency over the right hypochondrium on an abdominal radiograph, or inside the gallbladder lumen on computed tomography may suggest the presence of biliary gas.

In 1796 Walter [1] first described the star-shaped fissures in biliary calculi in vitro, but only in 1931 was the radiographic aspect of this phenomenon described [2,3].
Meyers and Donohue [4] associated the presence of fissures to both the rapid formation of calculi as well as to auto-fragmentation. Hinkel [5,6] radiographed post-cholecystectomy gallbladders and detected fissures in about 50% of gallstones. Most contained fluid, but about 46% contained some gas.
A series of cholecystolithiasis imaged by CT [7] determined the presence of gas in about 4% of calculi.

A star-shaped lucency in the right hypochondrium on an abdominal radiograph may be the only indication of non-calcium gallstones on an abdominal radiograph.
Likewise, identification of biliary calculi floating in bile on US may suggest gas-containing gallstones [8,9]. US may show a gallstone with posterior attenuation containing high-level echoes, suggesting the presence of gas. This presentation should not be mistaken for calcification [10].

Gas-containing gallstones observed on CT may present with a rim with attenuation values above, below or identical to those of surrounding bile [11].
On occasion calculi can be indistinguishable from the surrounding bile in CT, being isodense to bile, and tri-radiated lucencies can indicate the presence of lithiasis [9,10].
In a CT study of 21 calculi central gas collections usually presented with negative attenuation values as low as -290 HU [11] . Only densities under -100 HU are considered to be revealing, and when between -100 and 0 HU they are considered not precise, probably the result of a mix of gas and fluid within fissures (7,12).
Becker’s study [11] shows that CT findings differ with collimation, concluding that on 8mm-collimation images round or oval lucencies replace the star-shaped lucencies seen wit a 2mm-collimation.
Differential Diagnosis List
Fractured sternum; 3 gas-containing biliary calculi (with “Mercedes-Benz” sign).
Final Diagnosis
Fractured sternum; 3 gas-containing biliary calculi (with “Mercedes-Benz” sign).
Case information
DOI: 10.1594/EURORAD/CASE.7689
ISSN: 1563-4086