Background. In about 20 to 40 percent of cases of acute pancreatitis, no cause can be found, and these are labeled idiopathic. In this study, we sought to determine the frequency with which patients with acute idiopathic pancreatitis have biliary sludge, a suspension of cholesterol monohydrate crystals or calcium bilirubinate granules that is found predominantly in the gallbladder. Methods. Between 1980 and 1988, we prospectively studied 86 patients who had acute pancreatitis. In patients with no known cause of pancreatitis and no ultrasonographic evidence of gallstones or dilatation of the biliary ducts, we determined how often biliary sludge was present and its subsequent fate by repeated microscopical examinations of bile samples and abdominal ultrasonography. The outcome of patients treated by cholecystectomy or papillotomy was compared with that of untreated patients. Results. The pancreatitis was considered idiopathic in 31 of the 86 patients (36 percent), of whom 23 had microscopical evidence of biliary sludge. Biliary sludge was detected by ultrasonography in only 11 of the 23 patients (48 percent). The sludge detected by ultrasonography was composed of calcium bilirubinate granules in 10 and cholesterol monohydrate crystals in 1 (P = 0.003). Calcium bilirubinate granules were found more frequently in men (nine men vs. four women, P < 0.001). Of the 21 patients in whom biliary sludge was the only finding (2 patients also had dilated bile ducts when restudied), the 6 treated by cholecystectomy and the 4 treated by papillotomy had fewer recurrences of acute pancreatitis during follow-up (up to seven years) than the 11 untreated patients (P = 0.011). The presence of biliary sludge appeared to increase the likelihood of recurrent attacks of pancreatitis (P = 0.020). Conclusions. Biliary sludge is an underestimated cause of acute idiopathic pancreatitis.
