Crocodile Jaw Appearance May Indicate Annular Pancreas Annular Pancreas in Adults

Objective: To describe the prevalence of and findings associated with annular pancreas on CT, MRI, and endoscopic retrograde cholangiopancreatography (ERCP). Design: Retrospective analysis. Participants: 42 patients with annular pancreas who underwent CT, MRI, or ERCP made up the study group. The control group consisted of 30 patients evaluated for nonspecific upper abdominal pain who had a normal pancreatic head on CT or MRI and normal ductal anatomy at ERCP. Methods: 22 CT, 13 MRI, and 29 ERCP examinations were performed. CT examinations were performed with a 4or 16-MDCT scanner. A 1.5T system was used for MRI examinations. Imaging sequences included T1weighted in-phase and out-of-phase and T2-weighted turbo spin-echo. T1-weighted fat suppressed volumetric acquisition images were obtained before and during arterial, venous, and 3-minute phases following intravenous contrast administration. Other acquired images included 2D 40-mm thick slab MRCP, 3D navigator-corrected MRCP, and secretin-enhanced MRCP images. Two radiologists reviewed the CT and MRI images. Results/Conclusions: In the study group, the indications for CT, MRI, and ERCP imaging included abdominal pain, gastric outlet obstruction, abnormal liver function tests, preoperative evaluation of pancreatic carcinoma or intraductal mucinous neoplasm, pancreatic head mass, hepatocellular carcinoma screening, liver lesion characterization, and weight loss. Patients in the control group had final diagnoses of no abnormality, biliary dyskinesia, and sphincter of Oddi dysfunction. Of the 42 patients with annular pancreas, 33 had a complete annular pancreas, and the remaining 9 patients had incomplete annular pancreas. The complete annular pancreas was diagnosed using ERCP (n=18) and with CT, MRI, or both (n=15). The complete annular pancreas always surrounded the second part of the duodenum. The presence of pancreatic tissue posterolateral to the duodenum was 92% sensitive and 100% specific for annular pancreas. The incomplete annular pancreas was confirmed at surgery in 3 patients and with ERCP in 6 patients. The configuration of the pancreatic head surrounding the duodenum was variable and was circular or triangular with a crocodile jaw appearance. The risk of gastric outlet obstruction was 33%, similar to that of complete annular pancreas. There was a higher prevalence of other pathologic conditions of the pancreas, most notably pancreas divisum and chronic pancreatitis. Reviewer's Comments: The results of this study are useful in demonstrating that an annular pancreas can be diagnosed when a complete or an incomplete ring of pancreatic tissue surrounds the duodenum. A limitation reported in this study was the retrospective study design. (Reviewer-John C. Sabatino, MD).