A 45-year-old woman came into the emergency department presenting with a 1-h history of sudden onset, severe epigastric pain radiating to the back. She reports having had a similar episode of abdominal pain after eating a fatty meal several months ago, but the pain was duller and resolved after a few hours. She has a past medical history significant only for hypertriglyceridemia. On presentation, serum amylase and lipase were 50 U/L and 100 U/L, respectively, but both had increased to >400 U/L when taken 6 h later. The patient continued to have persistent severe pain over the next 48 h, along with fever and nausea, despite aggressive hydration. Contrast-enhanced CT imaging (CECT) showed evidence of a stone in the distal common bile duct. With the possibility of severe acute pancreatitis and obstructing gallstone, the consulting gastroenterologist decided to admit the patient for an endoscopic retrograde cholangiopancreatography (ERCP) procedure.

This is a patient who fulfills the diagnostic criteria for acute pancreatitis (AP) given both the history of sudden, severe pain radiating to the back and having elevated pancreatic enzymes, i.e., amylase and lipase. The most common causes of AP are gallstones (40–70%) and alcohol (25–35%). Due to the high prevalence of gallstones, which often cause recurrent disease, abdominal ultrasound should be performed on all patients presenting with AP. Ultrasound detects gallstones as small as 2 mm with a sensitivity >95% and can also rapidly be performed at the bedside [1]. If abdominal ultrasound is not performed upon presentation, it is important to get a thorough history.

Patients with acute biliary pancreatitis, or pancreatitis caused by gallstones, often have had episodes of biliary colic before presenting with AP. Biliary colic occurs when the gallbladder contracts against a cystic duct obstructed by a gallstone. Similar to this patient, biliary colic causes right upper quadrant pain that may radiate to the shoulder and often occurs after a fatty meal. The pain, however, often does not last beyond a few hours. There may be associated nausea and vomiting as well.

Identifying risk factors for developing gallstones is also important for diagnosis. These include age >40, female sex, family history, obesity, and certain ethnicities including Northern Europeans and Hispanics [2]. A simple pneumonic often used to remember the risk factors is “fat, forty, female, fertile, and fair.” Lab criteria for diagnosis require serum amylase and/or lipase greater than three times the upper limit of normal. Serum amylase cannot be used alone for diagnosing AP, and serum lipase is preferred. It should be noted that both enzymes rise within a few hours after onset of symptoms. Additional tests that can help differentiate biliary pancreatitis from other causes of pancreatitis include the liver function tests. For example, a recent study has shown that the specificity of a serum ALT >150 IU/L for diagnosing gallstone pancreatitis was 96%, although the sensitivity is only about 50% [3].

Gallstones that cause biliary colic, or even full-blown AP, most often pass to the duodenum and are lost in stool. There is a minority of patients, however, that can have ongoing pancreatic duct and/or biliary tree obstruction due to having persistent gallstones. This can lead to severe AP, as occurred in our patient, and/or cholangitis, which is an infection of the biliary tract that often causes fever, jaundice, and right upper quadrant pain. The diagnosis of severe AP is made when patients fail to improve clinically within the first 48–72 h despite appropriate initial therapy, such as IV hydration [4]. Those that fail to improve often have persistent severe pain, fever, nausea, vomiting, or are unable to start oral feeding.

Although imaging beyond an ultrasound is usually not recommended when a patient initially presents with AP as most have a mild, uncomplicated course, this patient has not been getting better and has many risk factors for having a retained gallstone causing continued pancreatic inflammation and damage. In this setting, further investigation is required and CECT or MRI imaging is the next step. CECT imaging has a 90% sensitivity and specificity for diagnosing AP. Furthermore, it may help visualize bile duct stones, as it did in this patient, and also allows providers to assess the extent of pancreatic damage, which can help predict the severity of disease. The CT finding of CBD stones may have sensitivity as high as 80% [5]. MRI, on the hand, is better able to detect gallstones in the bile ducts down to 3 mm diameter by employing magnetic resonance cholangiopancreatography (MRCP). MRI is also more advantageous to use in patients with a contrast allergy and/or renal disease [6]. MRI, however, has a longer scanning time compared to the CT and is often difficult to perform in severely ill patients.

In conclusion, this patient, with a history of biliary colic and who has several risk factors for developing gallstones, already had a high probability of acute biliary pancreatitis. Ultimately, this was confirmed with imaging.