CASE SUMMARY

A 54-year-old woman with a history of diabetes mellitus presented in diabetic ketoacidosis. A source of infection was not found on the initial evaluation, despite an elevated white blood cell count. The following day she began to complain of diffuse abdominal pain. An abdominal ultrasound was performed, which was unremarkable except for the fact that the gallbladder was not visualized (figure 1). Because of worsening abdominal pain, supine and left lateral decubitus radio-graphs of the abdomen were performed (figure 2), followed by an abdominal computed tomo-graphy (CT) scan (figure 3).

DIAGNOSIS

Emphysematous cholecystitis

IMAGING FINDINGS

The ultrasound reveals highly reflective echoes in the gallbladder fossa with associated reverberation artifact, consistent with gas (figure 1). The supine radiograph of the abdomen reveals curvilinear lucencies outlining the margin of the gallbladder (figure 2A). On the left lateral decubitus radiograph, a gas/fluid level is demonstrated within the lumen of the gallbladder (figure 2B). The CT scan shows gas within the wall and the lumen of the gallbladder, as well as within the extrahepatic biliary system (figure 3).

DISCUSSION

Emphysematous cholecystitis (EC) is a relatively rare form of acute cholecystitis in which the gallbladder wall and/or lumen contain gas. In some cases, the pericholecystic tissues and biliary system also contain gas. The development of EC is attributed to bacterial invasion of the gallbladder wall by gas-forming bacteria. The most common micro-organisms implicated are Clostridium species. Escherichia coli is also frequently present, either alone or as a copathogen.1 EC is more common among patients with diabetes mellitus (up to 50%) and is associated with increased morbidity and mortality compared with acute non-emphysematous cholecystitis.2 The increase in morbidity and mortality is likely related to the increased prevalence of gangrene and perforation of the gallbladder. Unlike nonemphysematous cholecystitis, EC is more common in males than females. EC is less likely to be associated with gallstones (80% have stones) than nonemphysematous cholecystitis.3 Vascular insuf-ficiency has been suggested as the primary insult in most cases, with the ischemic gallbladder providing an opportunity for gas-forming micro-organisms to proliferate.1-3

The clinical presentation of EC is usually similar to nonemphysematous cholecystitis.1,2 However, there may be a surprising paucity of symptoms in some patients. No author has reported a case in which the diagnosis of EC was strongly suspected before being made radiographically or surgically.1

Although plain radiographs are often not obtained in suspected cases of cholecystitis, they provide an opportunity to identify abnormal collections of gas in the gallbladder fossa. Plain radiographic findings of EC have been described in three stages: gas within the gallbladder lumen (stage 1), the wall (stage 2), and the pericholecystic tissues (stage 3).1,2 The differential diagnosis of air in the gallbladder lumen alone includes a fistula between the gallbladder or biliary system and gastrointestinal tract, enterobiliary anastomosis, incompetent sphincter of Oddi, and recent endoscopic retrograde cholangiopancreatogram.4

Ultrasound is frequently the first modality utilized in a patient with clinical suspicion of acute cholecystitis. Abnormal ultrasound findings may be present before gas becomes visible on plain radiographs.3,5,6 These findings include a reverberation or "comet-tail" artifact caused by an abrupt change of acoustic impedance at a soft tissue/gas interface.5 The gallbladder itself is usually not visualized, due to reflection of sound waves by gas collections within the wall and/or lumen. An "effervescent" appearance of the gallbladder has also been described, with multiple tiny echogenic foci (gas bubbles) rising from the dependent portion of the gallbladder lumen. The appearance has been described as being similar to "champagne bubbles."6

CT is frequently used to evaluate abdominal pathology and is virtually diagnostic for EC. It may also serve to identify abnormal collections of gas or calcifications that prevent sonographic visualization of the gallbladder.

We would like to emphasize that failure to identify the gallbladder during abdominal ultrasound of a fasting patient with abdominal symptoms (particularly the diabetic and elderly) should suggest the diagnosis of emphysematous cholecystitis. A careful search for abnormal collections of gas in the gallbladder fossa during ultrasound examination, or further study with plain radiographs and/or CT may save valuable time during management of patients with this condition.