Gas‐containing gallstones: a radiological finding

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A 68‐year‐old man presented with a 3‐day history of epigastric pain described as a dull ache radiating to the back. No associated fevers, nausea and vomiting or change in bowel habit. No previous history of gallstones. On examination, he was afebrile and tender in the right upper quadrant. Blood investigations showed a raised white cell count of 17.8 × 109/L, mildly deranged liver function tests, bilirubin 29 μmol/L, gamma glutamyl transpeptidase 327 U/L, alkaline phosphatase 191 U/L and a lipase of 31 U/L.
Upper abdominal ultrasound showed multiple gallstones within the gallbladder with one gallstone lodged in the gallbladder neck. No gallbladder wall thickening, common bile duct dilatation or other features of cholecystitis were seen.
The patient's pain persisted and his liver function tests remained elevated; a computed tomography (CT) of the abdomen was conducted. Gas was seen within the gall bladder, leading to a differential diagnosis of emphysematous cholecystitis or pneumobilia. Further examination of the images revealed that the gas was contained within the gallstones (Figs 1).
The patient was initially treated as acute cholecystitis with intravenous antibiotics. The patient remained afebrile and his white cell count normalized. Given the clinical improvement and the lack of radiological evidence for cholecystitis, antibiotics were ceased. The patient continued to improve with conservative management of biliary colic. The patient was discharged and underwent an elective cholecystectomy later that year. Pathological examination of the gallbladder showed evidence of subacute inflammation and contained multiple gallstones.
Breuer first described gas‐containing gallstones in 1931.1 During the formation of gallstones, 50% will contain fissures, a by‐product of the crystallization process. Early data showed that approximately half of the gallstones that contained fissures would contain gas and the other half would be filled with liquid.2 However, more recent studies looking at the incidence of gallstones seen on routine CT of the abdomen found that 4% of patients with gallstones had gas‐containing calculi, suggesting gas‐containing gallstones are less common than first thought.5
Gas‐containing gallstones were demonstrated in vitro as early as 1796 but Breuer was the first person in 1931 to successfully recognize stellate radiolucency on abdominal X‐ray as gas‐containing gallstones.4 The appearance of gas‐containing gallstones has since been described as Mercedes Benz, crow's foot or star sign.
An important differential diagnosis to consider when gas is seen within the gallbladder is emphysematous cholecystitis. Emphysematous cholecystitis is a rare complication of acute cholecystitis where gallbladder necrosis or the presence of gas‐producing bacteria means that gas can be seen within the gallbladder wall or lumen,6 whereas in the case of gas‐containing gallstones, the gas is located within the gallstone.
Classic acute cholecystitis is common and has a mortality rate of 4%, whereas emphysematous cholecystitis is rare, with an incidence around 1%, but has a mortality rate of approximately 15%.7 The increase in mortality is due to the deceptively minimal clinical signs and a higher rate of gallbladder ischaemia and perforation.5
Gas‐containing gallstones are relatively common, but no more dangerous than non‐gas‐containing gallstones. Emphysematous cholecystitis is of low prevalence but high in mortality. It is important to recognize the difference between these two pathologies and to act promptly if emphysematous cholecystitis is suspected. The patient in this case had a raised white cell count initially but had no other clinical signs of sepsis. There were also no radiological signs, such as pericholecystic fluid collection or gallbladder wall thickening, to support the differential diagnoses of acute cholecystitis. Importantly, the gas seen on CT was within the gallstones and not within the wall or lumen of the gallbladder. Therefore, we can be confident that this is a case of gas‐containing gallstones causing biliary colic.

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