Biliary Intervention in Acute Gallstone Pancreatitis

Diagnosis of Acute Gallstone Pancreatitis

The effective use of ERCP intervention for the management of AGP necessitates differentiating AGP from other causes of AP. As with all examples of diagnostic investigation, this requires a combination of accurate history taking, physical examination, and interpretation of laboratory values and imaging. A history of cholelithiasis or symptoms consistent with biliary pain is suggestive, but not diagnostic, of a biliary etiology. The physical examination is not specific in distinguishing AGP from other causes. However, concurrent cholecystitis producing Murphy's sign and/or signs of cholangitis are findings that can increase the likelihood that gallstones are the etiology of a patient's pancreatitis. Much of the published literature involves the use of biochemical values and imaging studies for predicting a biliary etiology of AP.

Serum amylase levels have been shown to be higher in patients with AGP than in those with alcohol-related AP, and authors have postulated that a serum amylase level >1000 U/L indicates a biliary cause of AP. The presence of elevated liver chemistries has been studied and a meta-analysis demonstrated that elevations of alanine aminotransferase (ALT) levels >3 times normal at the time of presentation are suggestive of AGP. This study also found that total bilirubin and alkaline phosphatase levels were not useful and aspartate aminotransferase (AST) was no more useful than ALT in diagnosing AGP. In addition, once AGP is established, patients with rising serum pancreatic enzymes or liver tests have a four times greater risk of persistent CBD stones and approximately three times greater risk of complications compared with patients with stable or declining laboratory values.

Demonstration of cholelithiasis by imaging can further support the diagnosis of AGP. Abdominal ultrasonography is the preferred initial imaging study, given its high sensitivity and specificity for gallstones. In the setting of AP, however, this sensitivity can be reduced by the presence of overlying air-filled loops of bowel. A recent study found that abdominal ultrasonography in the setting of AP remains a very sensitive test (86%) and, when combined with an elevation of ALT >80 IU/L, is 98% sensitive and 100% specific for a biliary etiology. The lack of biliary dilatation on ultrasonography does not exclude choledocholithiasis in the setting of AP, especially in the first 48 hours of an attack.

The attendant risks of ERCP and the gold standard for detecting choledocholithiasis have prompted the study of magnetic resonance cholangiopancreatography (MRCP) and endoscopic ultrasonography (EUS) as alternative, safer diagnostic modalities. MRCP has high sensitivity (84% to 95%) and high specificity (96% to 100%) for the diagnosis of common duct stones. The most common cause of a false-negative MRCP is gallstone size <5 mm. A prospective study comparing multiple imaging modalities (abdominal ultrasonography, computed tomography [CT], MRCP, ERCP, and intraductal ultrasonography) showed an 80% sensitivity for MRCP at detecting choledocholithiasis with 90.6% agreement between ERCP and MRCP. EUS demonstrates equivalent accuracy to MRCP for the detection of choledocholithiasis. EUS can detect choledocholithiasis at a sensitivity of 98% with 99% specificity. In a recent analysis, the results of EUS were helpful in identifying a biliary cause for AP in half of the patients with unknown etiology and negative imaging.

The exact role of each of these modalities in the diagnosis of AGP and the patient groups to which they should be individually applied must be clarified in future studies and is inevitably dependent on local availability and logistics.

Prediction of Common Bile Duct Stones

Many scoring systems and prognostic factors are available to assess the likelihood of a CBD stone in AP. Although no single prediction model has been validated as better than another, the American Society for Gastrointestinal Endoscopy (ASGE) published guidelines in 2010 to help risk stratify patients based on an algorithm created by Maple et al. ( Box 53.1 ). Patients are categorized as low risk, intermediate risk, or high risk for choledocholithiasis. Those who are high risk should go directly to ERCP and then cholecystectomy. Intermediate-risk patients should be further evaluated with EUS or MRCP. Low-risk patients are considered to have <10% probability of having a CBD stone. If imaging shows sludge or gallstones in the gallbladder and the patient is a good surgical candidate, he or she should proceed directly to cholecystectomy. Ultimately, a CBD stone found on imaging is the best marker for choledocholithiasis.