A 59-year-old woman arrives at the emergency department due to right upper quadrant abdominal pain, nausea, vomiting, and fever since yesterday. She has no hematemesis, constipation, diarrhea, or shortness of breath. The patient's medical history is significant for hypertension, stable coronary artery disease, and type 2 diabetes mellitus. She does not use tobacco, alcohol, or illicit drugs. Temperature is 38.9 C (102 F), blood pressure is 112/76 mm Hg, pulse is 101/min, and respirations are 18/min. Oxygen saturation is 96% on room air. BMI is 34 kg/m². Cardiopulmonary examination shows no abnormalities. There is marked tenderness and voluntary guarding to palpation in the right upper quadrant of the abdomen. Laboratory results are as follows. Abdominal imaging demonstrates a distended gallbladder with gas in the gallbladder wall and lumen. There is no gas in the biliary tree. What is the most likely diagnosis in this patient?

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11ec25c8_d83b_fef6_bc81_77c10b55478a_MD0003_00 This patient with fever, right upper quadrant (RUQ) pain, and gas in the gallbladder wall has clinical manifestations of acute emphysematous cholecystitis, a life-threatening form of acute cholecystitis due to infection with gas-forming bacteria (eg, Clostridium, some Escherichia coli strains). Predisposing factors include relative immunosuppression (eg, age >50, diabetes mellitus) and vascular disease (eg, compromised cystic artery blood supply, atherosclerosis). Crepitus in the abdominal wall adjacent to the gallbladder is occasionally detectable. Complications include gangrene and perforation, the latter of which may transiently relieve pain but subsequently result in peritoneal signs. Diagnosis is confirmed with imaging demonstrating air-fluid levels in the gallbladder (as gas leaks into it), gas in the gallbladder wall, and occasionally pneumobilia (air within the hepatobiliary system). However, in patients with emphysematous cholecystitis, unlike other forms of acute cholecystitis, ultrasound is less sensitive due to the modality's poor visualization of air-filled structures; extensive gas in the gallbladder wall may be falsely interpreted as failure to identify the gallbladder due to overlying bowel loops. Laboratory findings include mild to moderate unconjugated hyperbilirubinemia (eg, from Clostridium-induced hemolysis) and a small elevation in aminotransferases. Treatment requires emergency cholecystectomy and broad-spectrum parenteral antibiotic therapy (eg, piperacillin-tazobactam). air-fluid levels (Choice A) Although acute cholangitis (usually from common bile duct obstruction) is also characterized by high fever and RUQ pain, jaundice is much more common (Charcot triad), significant elevations in alkaline phosphatase and conjugated bilirubin would be more likely, and imaging would show bile duct dilation without gas in the biliary tree or gallbladder wall. (Choices B and D) Biliary-enteric fistulas are extremely rare and typically occur due to pressure ulceration from chronic gallstone disease, not acute cholecystitis. They cause pneumobilia but would not be expected to cause gas within the gallbladder wall itself (intramural gas) and are not typically associated with fevers or sepsis. Large bowel fistulas are characterized by bile acid diarrhea whereas fistulas with the small bowel are often asymptomatic but may cause gallstone ileus, which presents with symptoms of intermittent bowel obstruction (eg, nausea, diffuse abdominal pain) over several days as the gallstone moves through the intestines. (Choice E) Peptic ulcer perforation would be associated with free air under the diaphragm, not air-fluid levels or gas shadowing in the gallbladder. Educational objective: Emphysematous cholecystitis is a life-threatening form of acute cholecystitis that occurs more commonly in patients with immunosuppression (eg, diabetes) or vascular disease. It arises due to infection of the gallbladder wall with gas-forming bacteria and requires emergency cholecystectomy. References: Emphysematous cholecystitis. (http://www.ncbi.nlm.nih.gov/pubmed/22007119) Emphysematous cholecystitis: a case report. (http://www.ncbi.nlm.nih.gov/pubmed/18687128)

A 59-Year-Old Woman Arrives at the Emergency Department Due to Right