FDG-PET Findings of Intraductal Oncocytic Papillary Neoplasms of the Pancreas: Two Case Reports

Intraductal oncocytic papillary neoplasm (IOPN) of the pancreas is a rare pancreatic tumor. To date, there have been three case reports of IOPN which showed strong positivity on 18F-fluorodeoxyglucose positron emission tomography (FDG-PET), raising the possibility of distinguishing IOPNs from other intraductal papillary mucinous neoplasms (IPMNs) using FDG-PET. However, all three cases had large tumors, approximately 10 cm in diameter, and there are no case reports of FDG-PET findings of small IOPNs, i.e. tumors the average size of malignant IPMNs (3-5 cm). We report two cases with IOPN of average size with FDG-PET findings. Computed tomography (CT) showed a multilocular cystic lesion 4 cm in diameter with a mural nodule 1 cm in diameter (case 1) and a cystic lesion 5 cm in diameter with a papillary mural nodule 4 cm in diameter (case 2). FDG-PET showed abnormal uptake at the same location as the pancreatic tumor revealed by CT in both cases. The maximum standardized uptake values of the lesions were 3.4 and 4.2, respectively. Surgical resection was performed and the tumor was diagnosed as IOPN with carcinoma in situ (case 1) and IOPN with minimal invasion (case 2). FDG-PET may be useful for diagnosing malignancy in IOPN, as it is in IPMN. However, in our two cases, strong accumulation was not observed in the IOPNs, which were within the average size range of malignant IPMNs.