Pancreatic pseudocysts are an important sequelae of pancreatitis; although typically occurring between the pancreas and stomach, rarely the path of pancreatic enzymes leads them elsewhere. Intramural pseudocysts of the GI tract are rare, and there are no formal guidelines for their management. Here we discuss our experience with a large duodenal intramural pseudocyst. A 52 year-old man was transferred to our facility for further evaluation of a pancreatic pseudocyst. Since his initial gallstone pancreatitis 10 months prior, he had episodes of pancreatitis every 6 weeks, treated at his local hospital. He was symptomatic with elevated lipase, and was treated with fluids and analgesia prior to transfer. A likely pseudocyst was seen on prior CT. A CTA was performed to rule out a pseudoaneurysm and to provide an updated view of the lesion. This showed a 6.1cm mixed cystic and solid mass associated with the head of the pancreas, encasing the duodenum, producing some mass effect but without biliary ductal dilation. (Figure 1) There was no evidence of pseudoaneurysm. EGD revealed extrinsic compression in the duodenal sweep and second portion of the duodenum. EUS revealed a large complex intramural cystic lesion surrounded by the muscularis propria, with septations and solid/debris components. (Figure 2) Chronic changes of pancreatitis were evident, with no discernible mass or pathologic lymphadenopathy. EUS-guided FNA of the cystic component yielded serosanguinous fluid with a high amylase and RBC count and low CEA. Additional samples were taken from the solid component of the cyst, which showed benign columnar epithelial cells, mixed inflammatory cells, and blood. The patient's symptoms improved, and he was transferred back to his local hospital. Duodenal intramural pseudocysts are rare, but should be considered when a duodenal lesion or obstruction is found. Possible sequelae include obstruction, rupture into the bowel, and pseudoaneurysm. We found EGD with EUS appropriate and definitive in the case, to determine if obstruction was present, evaluate the relationship with the duodenal wall, and to sample the fluid for analysis. On return to his local hospital, we recommended conservative management, but to repeat EUS-guided aspiration if obstruction occurred. We recommended against drain placement, as with no well-defined wall, perforation is possible. We also recommended cholecystectomy, given the initial etiology of his pancreatitis was cholelithiasis.Figure: CTA demonstrating duodenal intramural pseudocyst; arising from the pancreatic head and partially encapsulating the duodenum.Figure: EUS of duodenal intramural pseudocyst. Muscularis propria seen surrounding the lesion.