Muscular rim sign at endoscopic ultrasound in a patient with a suspected cyst of the pancreatic head

A 67 years old male patient was referred in September 2019 to the Gastroenterology and Endoscopy Unit of the Sahlgrenska University Hospital, in Göteborg (Sweden), to undergo an endoscopic ultrasound (EUS) examination. The patient was asymptomatic, without other relevant gastroenterological comorbidities and referred for the suspicion of a pancreatic cyst and/or intraductal papillary mucinous neoplasia (IPMN) of the pancreatic head; the suspicion was raised by a recent magnetic resonance imaging (MRI) examination performed in our center for other reasons. Multiple EUS scans excluded any pancreatic cysts. The endoscopic view of the duodenum confirmed the presence of both the minor and the major duodenal papilla. However, just below the major duodenal papilla, a mucosal bulging extended for 2.5 centimeters, with normal mucosa and with a papilla-like orifice in the proximal part was found (Figure 1a) and evaluated with EUS (Figure 1b). What is the diagnosis on the basis of the EUS image?

Keywords: duodenal mucosa, endoscopic ultrasonography, pancreatic pseudocyst, duplication cyst.