eMedicine Specialties > Radiology > Gastrointestinal

Cholecystitis, Acalculous: Imaging

Author: J David Lane, MD, RT, Chief, CMH Vascular and Interventional Radiology, Wisconsin Radiology Specialists, SC; Former Section Chief, Assistant Professor, Vascular and Interventional Radiology, Walter Reed Army Medical Center, Uniformed Services University of the Health Sciences
Coauthor(s): Nick Lomis, MD, QI Coordinator, Diagnostic Radiology Service, Assistant Chief, Interventional Radiology, Diagnostic Radiology, Interventional Radiology Section, Walter Reed Army Medical Center
Contributor Information and Disclosures

Updated: Oct 16, 2008

Radiography

Findings

Plain film radiography is of limited use in the diagnosis of acute acalculous cholecystitis. Emphysematous cholecystitis may occur as a complication of acute cholecystitis; more than one half of such cases occur in the setting of acalculous disease. This form of complicated cholecystitis typically is seen in older male patients with diabetes. On upright abdominal radiographs, acute acalculous cholecystitis (AAC) may be evinced by the presence of an air-fluid level in the right upper quadrant; such a finding represents gas in the gallbladder lumen. The presence of intramural gas is indicated by findings of a curvilinear gas collection that conforms to the gallbladder wall. Gas is visualized only in more severe cases on plain film. US and CT are much more useful. The presence of gas is often associated with gangrene and perforation (see Images 1, 9, 14).

Computed Tomography

Findings

CT often is performed as the diagnostic examination of choice in patients presenting with abdominal pain in the critical care setting or in patients with fever or leukocytosis of undefined etiology. CT offers the advantage of evaluating the entire chest and abdomen; it has the disadvantage of requiring transport to the scanner. One should be familiar with the CT signs that suggest acalculous cholecystitis in the appropriate clinical setting (see Images 2, 3, 10).

The diagnosis of acute acalculous cholecystitis (AAC) with CT requires that 2 major diagnostic criteria be met or, alternatively, that 1 major criterion and 2 minor criteria be met. These criteria are as follows:

• Major criteria
  • Gallbladder wall thickening greater than 3 mm
  • Subserosal halo (ie, gallbladder wall edema)
  • Pericholecystic fatty inflammation
  • Pericholecystic fluid (without ascites or hypoalbuminemia)
  • Mucosal sloughing
  • Intramural gas
• Minor criteria
  • Gallbladder distention (>5 cm transverse)
  • High-attenuation bile (sludge)

The normal gallbladder wall is barely perceptible as a thin enhancing rim on contrast-enhanced CT. In the absence of gallstones, imaging relies on ancillary findings of cholecystitis.

CT findings for patients with AAC are as follows:

• Gallbladder wall thickening
• Mucosal irregularity
• Luminal distention
• Increased bile density (biliary sludge)
• Intramural or intraluminal gas
• Intraluminal hemorrhage
• Localized pericholecystic fluid collections
• Inflammatory infiltration of pericholecystic fat
• Indistinctness of the liver-gallbladder interface

Degree of Confidence

Although mucosal sloughing and intramural gas are specific findings, they are observed infrequently. Isolated local pericholecystic fluid collections and pericholecystic inflammatory changes are relatively specific and suggest advanced disease, but they lose specificity in the setting of ascites, recent abdominal surgery, or anasarca.

Reported sensitivity and specificity vary but generally have been greater than 90-95%. As with other imaging modalities, the specificity of many of these findings is decreased in the typical populations at risk for acalculous cholecystitis because of comorbid conditions, such as recent surgery or trauma, multisystemic organ failure, ascites, or hypoalbuminemia.

Ultrasonography

Findings

Usually, sonography is the first examination performed in cases of possible acalculous cholecystitis. US has the advantages of being readily available, portable to the bedside, and able to identify other adjacent pathologies. Primary disadvantages of US include the high incidence of nonspecific abnormal examinations and the inability to survey the entire abdomen (see Images 6-8, 11-12).^8,9,10

The normal gallbladder has sonolucent bile and a thin wall; no localized pain is present. Sonographic signs compatible with acalculous cholecystitis include the following:

• Gallbladder wall thickening
• Sonographically localized tenderness over the gallbladder
• Subserosal edema
• Pericholecystic fluid
• Gallbladder distension
• Biliary sludge
• The presence of gas

Failure of the gallbladder to contract after the infusion of cholecystokinin has been reported as an additional criterion, but the response often is too variable to be of use in these patients.

The diagnosis of acute acalculous cholecystitis (AAC) with US requires that 2 major diagnostic criteria be met or, alternatively, that 1 major criterion and 2 minor criteria be met. These criteria are as follows:

• Major criteria
  • Gallbladder wall thickening greater than 3 mm
  • Striated gallbladder (ie, gallbladder wall edema)
  • Sonographic Murphy sign (ie, localized gallbladder tenderness)
  • Pericholecystic fluid (without ascites or hypoalbuminemia)
  • Mucosal sloughing
  • Intramural gas
• Minor criteria
  • Gallbladder distention (>5 cm transverse)
  • Echogenic bile (sludge)

Gallbladder wall thickness should be measured in the transverse plane, provided the gallbladder has not collapsed. The presence of ascites or decreased oncotic pressure (as occurs in patients with hypoalbuminemia) confuses the finding, unless the finding is markedly discordant. Similarly, the presence of pericholecystic fluid is not meaningful in the presence of generalized ascites; however, the occurrence of pericholecystic fluid as a localized finding often signifies advanced disease or perforation. The sonographic Murphy sign is the most specific sonographic finding, but often it cannot be evaluated because of the patient's clinical condition.

Following diagnostic needle aspiration of the gallbladder, results of bile Gram stain and culture are often normal; the sensitivity is less than 50%, and the results of culture are delayed. Therefore, the test is of limited value for the diagnosis of AAC. Culture is performed routinely at the time of therapeutic cholecystostomy and may guide antibiotic selection.

Degree of Confidence

The reported sensitivity and specificity of sonography in the evaluation of acalculous cholecystitis vary from 23-95% and 40-95%, respectively; this degree of variance occurs because of differences in patient populations, clinical courses, and imaging technologies employed over time. The sensitivity and specificity are greater than 90% in the subset of patients with acalculous cholecystitis who present in the outpatient setting.

Overall, the sensitivity and specificity approach 70%. As the proportion of patients in the critical care environment increases, the diagnostic accuracy decreases. Several studies have documented a high incidence of abnormal gallbladder sonograms in the ICU environment in asymptomatic patients who were not suspected of having acalculous cholecystitis.

At least 1 abnormal finding was seen in 50-85% of patients in this setting; 3 abnormal findings were seen in as many as 57% of patients. None of these patients had localized gallbladder tenderness by sonography. Serial sonography has been of benefit in some studies; the fact that the appearance on short-term follow-up images progressively worsens increases the specificity for diagnosis.

Nuclear Imaging

Findings

Hepatobiliary scintigraphy (HBS) is a physiologic test that evaluates hepatic bile formation, excretion, and ductal functional patency.

Imaging typically is performed with dynamic image acquisition for up to 4 hours following the intravenous (IV) administration of 5 mCi of a technetium-99m-labeled iminodiacetic acid derivative. Peak liver uptake is at 5-10 minutes, with subsequent gallbladder visualization by 20 minutes and duodenal visualization by 30 minutes (see Images 4-5).

If nonvisualization or questionable visualization of the gallbladder occurs but adequate hepatic uptake and excretion into the bowel are seen, IV morphine sulfate (0.04 mg/kg) may be administered at 30-40 minutes, with imaging carried out for up to 1 hour. This raises intrabiliary pressure by inducing contraction of the sphincter of Oddi and filling of the gallbladder, provided the cystic duct remains patent. A lateral view may be helpful if a question remains concerning gallbladder filling; the gallbladder is located anteriorly in this projection.

Some have attempted to improve accuracy by pretreating the patient with cholecystokinin infusion before performing HBS, so as to empty the distended gallbladder. HBS may be nondiagnostic in patients with liver failure and intrahepatic cholestasis of any cause because of the inability to conjugate and excrete the radiotracer.

Additional useful findings on cholescintigraphy include the presence of an area of increased pericholecystic radiotracer accumulation in the gallbladder fossa. This rim sign is associated with complications such as gangrene. Radiotracer extravasation rarely may be visualized in the setting of perforated gangrenous cholecystitis if the cystic duct remains patent.

Degree of Confidence

Hepatobiliary scintigraphy (HBS) is accurate in the diagnosis of calculous cholecystitis because the primary event is believed to be cystic duct obstruction. In cases of acalculous cholecystitis, functional obstruction usually occurs in the disease process but is variable and is not the primary process. Not surprisingly, the sensitivity and specificity of HBS are decreased in this setting.

In general, diagnostic quality studies with augmentation yield a sensitivity of 80-90% and a specificity of 90-100%.

False Positives/Negatives

The false-positive rate without pharmacologic augmentation is as high as 40% in some series, decreasing the specificity of the test. With morphine augmentation, the false-positive rate is decreased and the specificity is improved.

False-negative results (gallbladder filling in presence of acalculous cholecystitis) also may occur. Early filling of the gallbladder (within the first 30 min) excludes the diagnosis of acalculous cholecystitis, but with delayed filling after augmentation, the false-negative rate may be as high as 20%.

Angiography

Findings

No role exists for angiography in the diagnosis of acalculous cholecystitis.

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