Acute pancreatitis is a condition characterized by acute inflammation of the pancreas [1]. There are multiple risk factors and putative etiologies of acute pancreatitis; however, gallstones and alcohol are the identified etiology in up to 70% of cases [2,3]. In the Western world, gallstones are the leading cause of acute pancreatitis, causing up to 40% of cases [4]. For patients who harbor gallstones, the risk of biliary pancreatitis is up to 7% on long term follow-up [5]. Multiple hypotheses exist to explain the mechanism by which stones cause pancreatitis. Invariably, the stone must exit the gallbladder through the cystic duct and cause acute pancreatitis from being lodged at the pancreatobiliary junction or alternatively, a primary bile duct stone or secondary gallbladder stone may pass through the ampulla of Vater. Ampullary obstruction, local inflammation due to stone passage at the level of the ampulla of Vater and transient bile reflux into the pancreatic duct are all potential mechanisms to explain gallstone pancreatitis [6]. The risk of gallstone pancreatitis increases with smaller gallstones (allowing more unrestricted passage into the common bile duct and across the ampulla), and increased number of gallstones [7].

Acute pancreatitis of any etiology is diagnosed if two of the following three criteria are filled: (1) upper abdominal or back pain consistent with pancreas type pain, (2) increased pancreatic enzyme levels (lipase or amylase) > 3 times the upper limit of normal, and (3) pancreatic inflammation on abdominal imaging (usually computed tomography [CT] or magnetic resonance imaging) [8,9]. The abdominal pain is usually epigastric in location and radiates to the thoracic back, but may also be solely located in the back or in the left or right upper quadrants. Nausea and emesis are also often predominant symptoms [10]. The revised Atlanta classification is widely used to stratify the severity of acute pancreatitis, based on the presence or absence of local/systemic complications and the presence or absence of concomitant organ failure (Fig. 1) [9]. Due to this wide range in presentation, physical examination findings can vary significantly from patient to patient. In addition to the classically described clinical findings of abdominal tenderness, other clinical signs of ileus (distended, tympanic abdomen) and features of systemic inflammatory response syndrome (SIRS) may be encountered. Characteristics of biliary obstruction including dark urine, pale stools, icteric sclerae, excoriations from pruritis and jaundice may be valuable clues pointing towards gallstones as the etiological culprit for an episode of acute pancreatitis. The presence of risk factors for gallstones, such as older age, female gender, obesity, rapid weight loss, pregnancy or hormone therapy with estrogen may also increase the level of suspicion for biliary pancreatitis [11]. Elevated liver tests at the time of presentation for acute pancreatitis also raises this suspicion. Specifically, an elevated alanine transaminase level more than three times upper limit of normal (with a greater level than the aspartate aminotransferase) is a relatively specific indication of a biliary etiology under appropriate circumstances [12].

ERCP is an endoscopic procedure that uses a side viewing duodenoscope which facilitates identification of the ampulla of Vater and cannulation of the biliary or pancreatic ductal system. Once cannulated, contrast is injected and, with fluoroscopic assistance, the biliary or pancreatic ducts may be visualized [20-22]. If there is suspicion or confirmation of cholangitis, ERCP allows for the aspiration of bile for culture and sensitivity studies, along with drainage of the biliary system by either removing bile duct stones or placing a biliary stent [23]. For management of choledocholithiasis, a sphincterotomy is performed, which involves cutting the biliary sphincter with an electrosurgical sphincterotome. Retrieval of the stones (Figs. 4 and 5) at ERCP is typically done using a balloon or basket, but larger stones may require further maneuvers such as endoscopic fragmentation with lithotripsy. Complete removal of the stones may not be feasible during an index ERCP (particularly if there is concern for ascending cholangitis), and these instances warrant a biliary stent to be placed to ensure drainage [12]. Advanced stone extraction maneuvers may be performed at a subsequent procedure.

Whether or not to pursue ERCP in the setting of gallstone pancreatitis is an important clinical decision. Routine performance of ERCP for all patients with gallstone pancreatitis is not recommended, except in certain situations [13]. Fig. 6 illustrates those factors that alter the likelihood of ongoing biliary obstruction, which may impact the decision to proceed with ERCP. If a very strong predictor for ongoing biliary obstruction is present, such as ascending cholangitis, choledocholithiasis seen on an imaging study or total bilirubin > 4 mg/dL, then ERCP is indicated [12,13,17]. If a strong predictor is present without the factors above (biliary dilation on imaging study or elevated bilirubin 1.8 to 4 mg/dL), then an adjunct imaging test for choledocholithiasis (EUS or MRCP) is indicated. In patients who do not satisfy the above criteria but there remains suspicion for ongoing biliary obstruction, a high-quality evaluation of the biliary system with MRCP or EUS is warranted. If that evaluation shows evidence of a common bile duct stone, then proceeding with ERCP is the preferred course. Aside from the above situations of ascending cholangitis or persistent biliary obstruction, ERCP is unlikely to change the course of the disease, nor prevent any local or systemic complications or mortality of acute pancreatitis [24] and is discouraged [25].

A recent study by Muangkaew et al. [26] as well as the Tokyo guidelines have noted that in cases of biliary pancreatitis with mild cholangitis, conservative medical management and delaying ERCP may not impact morbidity or mortality [27]. Nevertheless, if ERCP is readily available, we recommend prompt (within 48 hours of presentation) ERCP for all patients with gallstone pancreatitis and suspicion of ascending cholangitis.

The AGA recommends laparoscopic cholecystectomy during the index admission for gallstone pancreatitis, once the pancreatitis has resolved [28]. Cholecystectomy performed at this time has been shown to decrease the risk of recurrent biliary events (cholangitis, symptomatic cholelithiasis or choledocholithiasis, recurrent pancreatitis) and to decrease readmissions [29-31]. This is, however, not always feasible or prudent, especially in cases of moderate or severe pancreatitis. It is reasonable in scenarios of severe acute pancreatitis, pancreas necrosis or significant peripancreatic fluid collections to opt for a delayed cholecystectomy rather than one performed on index presentation. This approach is associated with lesser morbidity and mortality in these unique scenarios [32]. In certain circumstances a cholecystectomy may not be feasible or may be contraindicated. Examples include advanced age, decompensated cirrhosis or coagulopathy. An ERCP with biliary sphincterotomy or transpapillary biliary or gallbladder stent in these instances may prevent recurrence of biliary pancreatitis [12,33,34].

Gallstones are the most encountered cause of acute pancreatitis. Early management with appropriate triage and fluid resuscitation with detection of local or systemic complications is of paramount importance. In gallstone pancreatitis, the decision on the need and timing of procedural intervention is crucial. ERCP is indicated for ascending cholangitis or clear evidence of ongoing biliary obstruction in this setting. Finally, cholecystectomy is indicated during the index admission for most cases of acute gallstone pancreatitis.