The Common Vein Copyright 2008
The Mercedes-Benz sign refers to the finding of partial radiolucencies within gallstones in CT imaging. These lucencies have a stellate or star-like appearance, and resemble the Mercedes-Benz symbol, the source of this eponymous finding.
Structurally, these areas of lucency are caused by gas-containing fissures within gallstones. Typically stones are formed by cholesterol. Bile normally contains bile salts and cholesterol in a ratio that keeps stones from forming. As this ratio becomes imbalanced by various pathological processes, stones can begin to precipitate. They typically do so in a concentric pattern, growing into spherical structures. It is belived that as these calculi harden, their crystals undergo an internal “shrinkage” and condense. This leads to weaknesses and uneven lattice forces within the cholesterol cryystals, resulting in tiny fissures or cracks that allow gas to enter the calculi. Cracks are usually 3 radially symmetrical, though anywhere from 1 to 5 may be seen.
Functionally this process is thought to be particular to rapidly-forming gallstones, rather than slow-forming stones, which have more regular crystal structures.
Pathologically they do not infer any additional clinical significance.
The diagnosis is based usually on CT scan which is sensitive to the air density, but the sign was originally described on plain film and oral cholecystography.
The treatment of this type of stone follows the algorithms of nay stone in the gallbladder.’
|72715 gallbladder stones Mercedes Benz sign air in gallstones cholelithiasis CTscan Courtesy Ashley Davidoff MD|