E1992. Mimics of Pancreatic Neuroendocrine Tumours
  1. May Lim; Singapore General Hospital Department of Diagnostic Radiology
  2. Elizabeth Hui Ting Cheong; Singapore General Hospital Department of Diagnostic Radiology
  3. Albert Low; Singapore General Hospital Department of Diagnostic Radiology
Pancreatic neuroendocrine tumours (NETs) are amongst the top differential for a hypervascular lesion in the pancreas on a contrast enhanced computed tomography (CECT) study. However, there are several other pancreatic/peripancreatic hypervascular lesions that may be misdiagnosed as pancreatic NETs. These include duodenal gastrointestinal stromal tumours (GISTs), paragangliomas, intrapancreatic metastases, intrapancreatic spenule, and other pancreatic neoplasms. We discuss the unique imaging features of each of these lesions and their behaviour on nuclear imaging studies that aid in their differentiation from NETs.

Educational Goals / Teaching Points
To describe the classic imaging features of pancreatic NETs, and to recognise that there are several mimics of pancreatic NETs. At the end of the exhibit, we hope the reader will also be able to discuss the differential diagnoses for pancreatic/peripancreatic hypervascular lesions, and their unique imaging features on CECT and nuclear imaging studies.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
Pancreatic NETs classically appear as solid avidly enhancing intraparenchymal lesions best seen on arterial phase. They may be associated with main pancreatic duct obstruction, and larger lesions may be associated with a cystic component or central necrosis. In recent years, 68-Gallium(68 Ga) DOTATATE Positron Emission Tomography (PET)/CT scans have shown excellent results in visualizing NETs, thereby impacting subsequent management. On fluorine 18(18F) Fluorodeoxyglucose (FDG) PET/CT scans, only poorly differentiated NETs demonstrate tracer uptake. Other pancreatic intraparenchymal hyperenhancing lesions include metastases and intrapancreatic spenule. Pancreatic metastases should be considered as a differential in a patient with a history of malignancy. Primary malignancies that commonly metastasize to the liver include renal, melanoma, lung, breast and colorectal cancers. Appearance of the metastases on 18F FDG PET/CT scan usually parallels that of the primary tumour. Peripancreatic hyperenhancing lesions that may mimic pancreatic NET include duodenal GISTs and paragangliomas. Similar to NETs, these lesions may also be associated with a cystic component or central necrosis, although the presence of a fat plane between them and the pancreas should clue the reader in to an alternative diagnosis. Duodenal GISTs tend to grow exophytically outward from the duodenum towards the pancreas, do not show uptake on 68Ga-DOTATATE PET/CT scans. Peripancreatic paragangliomas are extremely rare, and may demonstrate early contrast filling of the draining veins on dynamic CT images. Unlike NETs, both lesions demonstrate avid tracer uptake on fluorine 18F FDG PET/CT scan.

There are myriad of pancreatic/peripancreatic hypervascular lesions that may mimic pancreatic NET on CECT. Attention to unique imaging features and correlation with nuclear medicine imaging will aid in arriving at an alternative diagnosis.