Pancreatic Lymphoepithelial Cyst With High ¹⁸F-Fluorodeoxyglucose (FDG) Uptake Mimicking Malignancy: A Case Report and Literature Review

We present a case of pancreatic lymphoepithelial cysts (LECs) with solid components that demonstrated ¹⁸F-fluorodeoxyglucose (FDG) uptake on positron emission tomography (PET). Reports of LECs with FDG uptake on PET are extremely limited, and their interpretation may be challenging due to potential confusion with malignancy. An 84-year-old man presented with nausea and abdominal discomfort. Laboratory tests revealed elevated carcinoembryonic antigen (CEA) and cancer antigen 19-9 (CA19-9) levels. Imaging studies showed a cystic mass arising from the pancreatic tail with enhancing solid components and a thickened wall. FDG PET demonstrated high uptake (maximum standardized uptake value (SUV_max) = 8.36) in the solid portion and thickened wall. Magnetic resonance imaging (MRI) showed multiple subcentimeter nodules with heterogeneous signal intensity and restricted diffusion. Magnetic resonance cholangiopancreatography demonstrated no obvious communication with the main pancreatic duct. The patient underwent surgery due to malignancy concerns, but histology confirmed benign LEC. The solid components consisted of lymphoid follicular hyperplasia without malignant features. In our case, the uptake corresponded to areas of follicular hyperplasia. FDG is taken up via glucose transporter type 1, which is known to be expressed in follicular dendritic cells, possibly explaining the PET findings. LECs are benign, but may exhibit FDG uptake due to lymphoid tissue proliferation, mimicking malignancy. Recognizing this phenomenon, in conjunction with a comprehensive interpretation of MRI findings, may improve diagnostic accuracy.