Metabolic signatures of malignant and non-malignant mass-forming lesions in the periampulla and pancreas in FDG PET/CT scan: an atlas with pathologic correlation

Positron emission tomography (PET) has been used for the characterization of pancreatic and periampullary lesions. Pancreatitis-associated inflammation affecting only a portion of the pancreas gives the appearance of a mass lesion on imaging. Consequently, the differential diagnosis between cancer and pancreatitis becomes a commonly encountered problem. Traditionally, PET was interpreted as positive (to denote malignancy) if fluorodeoxyglucose (FDG) activity in the pancreas exceeded background activity and as negative (to denote benign) if activity was less than or equal to background activity. However, the specificity was limited with this method of interpretation. A relatively wide overlap has been reported between semiquantitative uptake values obtained in cancers and those in inflammatory lesions. Also, the qualitative (metabolic patterns) and quantitative variables (standardized uptake values) have been complementary and at sometimes controversial to each other in various clinical situations. There is paucity of data in the literature highlighting the role of FDG PET/CT in characterization of such mass lesions. The primary aim of this pictorial review is to list the various pathologic processes of pancreas and periampulla that could be studied with FDG PET/CT and recognize the different FDG uptake patterns and apply this information to characterize the different lesions affecting the pancreas and periampulla. We have also discussed the limitations of conventional imaging and advantages of FDG PET/CT for the evaluation mass-forming lesions of the pancreas and periampulla.