Duplication cyst.On these coronal T2-weighted MR images, at lateral wall of 2nd portion of duodenum medial to gallbladder, smooth, thin-walled cystic structure (arrow) was noted. Duplication cysts are often encountered incidentally and may cause obstruction and pancreatitis because of their critical location. With MRI, cystic nature and relationship with adjacent structures can be revealed. Duplication cysts need to be differentiated from other cystic lesions (such as choledochal cysts and pancreatic pseudocysts) that may be seen in this location.