Endoscopic ultrasound diagnostic gain over computed tomography and magnetic resonance cholangiopancreatography in defining etiology of idiopathic acute pancreatitis

Abstract

Background: About 10%-30% of acute pancreatitis remain idiopathic (IAP) even after clinical and imaging tests, including abdominal ultrasound (US), contrast-enhanced computed tomography (CECT) and magnetic resonance cholangiopancreatography (MRCP). This is a relevant issue, as up to 20% of patients with IAP have recurrent episodes and 26% of them develop chronic pancreatitis. Few data are available on the role of EUS in clarifying the etiology of IAP after failure of one or more cross-sectional techniques.

Aim: To evaluate the diagnostic gain after failure of one or more previous cross-sectional exams.

Methods: We retrospectively collected data about consecutive patients with AP and at least one negative test between US, CECT and MRCP, who underwent linear EUS between January 2017 and December 2020. We investigated the EUS diagnostic yield and the EUS diagnostic gain over different combinations of these cross-sectional imaging techniques for the etiologic diagnosis of AP. Types and frequency of EUS diagnosis were also analyzed, and EUS diagnosis was compared with the clinical parameters. After EUS, patients were followed-up for a median of 31.5 mo to detect cases of pancreatitis recurrence.

Results: We enrolled 81 patients (63% males, mean age 61 ± 18, 23% with previous cholecystectomy, 17% with recurrent pancreatitis). Overall EUS diagnostic yield for AP etiological diagnosis was 79% (20% lithiasis, 31% acute on chronic pancreatitis, 14% pancreatic solid or cystic lesions, 5% pancreas divisum, 5% autoimmune pancreatitis, 5% ductal abnormalities), while 21% remained idiopathic. US, CECT and MRCP, taken alone or in combination, led to AP etiological diagnosis in 16 (20%) patients; among the remaining 65 patients, 49 (75%) obtained a diagnosis at EUS, with an overall EUS diagnostic gain of 61%. Sixty-eight patients had negative US; among them, EUS allowed etiological diagnosis in 59 (87%). Sixty-three patients had a negative CECT; among them, 47 (74%) obtained diagnosis with EUS. Twenty-four had a negative MRCP; among them, 20 (83%) had EUS diagnosis. Twenty-one had negative CT + MRCP, of which 17 (81%) had EUS diagnosis, with a EUS diagnostic gain of 63%. Patients with biliary etiology and without previous cholecystectomy had higher median values of alanine aminotransferase (154 vs 25, P = 0.010), aspartate aminotransferase (95 vs 29, P = 0.018), direct bilirubin (1.2 vs 0.6, P = 0.015), gamma-glutamyl transpeptidase (180 vs 48, P = 0.006) and alkaline phosphatase (150 vs 72, P = 0.015) Chronic pancreatitis diagnosis was more frequent in patients with recurrent pancreatitis at baseline (82% vs 21%, P < 0.001). During the follow-up, AP recurred in 3 patients, one of which remained idiopathic.

Conclusion: EUS is a good test to define AP etiology. It showed a 63% diagnostic gain over CECT + MRCP. In suitable patients, EUS should always be performed in cases of IAP. Further prospective studies are needed.

Keywords: Computed tomography; Diagnostic gain; Endoscopic ultrasound; Idiopathic acute pancreatitis; Magnetic resonance cholangiopancreatography.

Figure 1

Illustrative images of the main etiological diagnoses of acute pancreatitis obtained by endoscopic ultrasound. A: Choledocholithiasis: endoscopic ultrasound (EUS) images of a small (3-4 mm) shadowing stone located in the distal common bile duct, obtained from the bulb (on the left) and descending duodenum (on the right) stations; B: Early chronic pancreatitis: EUS image showed a lobular pancreatic parenchyma with hyperechoic strands and foci, with hyperechoic margins of the Wirsung’s duct, all of which are minor criteria for chronic pancreatitis; C: Anomalous pancreaticobiliary junction: EUS image from the descending duodenum showed the confluence of Wirsung’s duct and common bile duct into a long (15 mm) common channel (on the left). The anomaly was then confirmed by retrograde cholangiopancreatography (on the right), also showing lithiasis of the distal part of the common channel; D: Pancreatic lesion: EUS image of a small (15 mm) solid lesion located in the pancreatic head; the lesion appeared hypoechoic and with irregular / infiltrating margins and comes close to the portal venous confluence. Histology confirmed a pancreatic adenocarcinoma; E: Pancreas divisum: EUS image from the descending duodenum showed a dominant dorsal pancreatic duct (PD), draining in the minor papilla; F: Autoimmune pancreatitis: EUS image showed a diffuse hypoechoic pancreatic enlargement, with hypoechoic parenchymal margins, at the level of the body (clearly visible the splenic vessels on the left). After contrast enhancement, the pancreas showed homogeneous early hypervascularization. Histology obtained by fine-needle biopsy revealed inflammatory infiltrates, excluding cancer.