Differential diagnosis of periampullary carcinomas at MR imaging.

Periampullary carcinomas arise within 2 cm of the major duodenal papilla and comprise carcinomas of the ampulla, distal common bile duct, pancreas, and duodenum. Their clinical features and anatomic locations are similar, as are the therapeutic approaches; however, their long-term outcomes vary. Magnetic resonance (MR) images of 89 pathologically proved periampullary carcinomas (29 ampullary carcinomas, 27 distal common bile duct carcinomas, 21 pancreatic carcinomas, six duodenal carcinomas, and six unclassified carcinomas) were reviewed. Ampullary carcinoma manifests as a small mass, periductal thickening, or bulging of the duodenal papilla. Pancreatic carcinoma is characterized by a discrete parenchymal mass, which enhances poorly on dynamic gadolinium-enhanced images. Sometimes, two proximal and two distal pancreatic and biliary ducts appear as four separate ducts (the four-segment sign). Dilatation of side branches of the pancreatic ducts is frequently seen in pancreatic carcinoma but not in other periampullary carcinomas. Distal bile duct carcinoma manifests as luminal obliteration and wall thickening or as an intraductal polypoid mass. A dilated proximal bile duct, a nondilated distal bile duct, and a dilated or nondilated pancreatic duct may form the three-segment sign. MR cholangiopancreatography and sectional MR imaging are useful in determining the origins of periampullary carcinomas.