Imaging of Pancreatic Neuroendocrine Neoplasms

Abstract

Pancreatic neuroendocrine neoplasms (panNENs) represent the second most common pancreatic tumors. They are a heterogeneous group of neoplasms with varying clinical expression and biological behavior, from indolent to aggressive ones. PanNENs can be functioning or non-functioning in accordance with their ability or not to produce metabolically active hormones. They are histopathologically classified according to the 2017 World Health Organization (WHO) classification system. Although the final diagnosis of neuroendocrine tumor relies on histologic examination of biopsy or surgical specimens, both morphologic and functional imaging are crucial for patient care. Morphologic imaging with ultrasonography (US), computed tomography (CT) and magnetic resonance imaging (MRI) is used for initial evaluation and staging of disease, as well as surveillance and therapy monitoring. Functional imaging techniques with somatostatin receptor scintigraphy (SRS) and positron emission tomography (PET) are used for functional and metabolic assessment that is helpful for therapy management and post-therapeutic re-staging. This article reviews the morphological and functional imaging modalities now available and the imaging features of panNENs. Finally, future imaging challenges, such as radiomics analysis, are illustrated.

Keywords: abdominal radiology; computed tomography (CT); gastrointestinal radiology; magnetic resonance imaging (MRI); pancreatic neuroendocrine neoplasms (panNENs); positron emission tomography (PET); somatostatin receptor scintigraphy (SRS).

Figure 1

PanNET G1 according to the 2019 WHO classification. CT images in the transverse plane during the basal (a), the arterial (b), the portal venous (c) and the delay (d) phases show a small pancreatic hypervascularized tumor of the pancreatic tail with sharp margin (arrow).

Figure 2

Patient with liver metastases from poorly differentiated pancreatic neuroendocrine carcinoma. CT images in the transverse plane during the basal (a), the arterial (b) and portal (c) phases show a large mass developed in the pancreatic tail with atypical hypo-enhancing pattern (arrow). This lesion is associated with multiple liver metastases (arrowheads) that appear hypodense with rim enhancement during arterial phase (b). According to the poorly differentiated tumor feature, FDG PET/CT (e,f) shows high uptake in pancreatic lesion while Somatostatin Receptor Scintigraphy with ¹¹¹-pentetrotide is negative (d).

Figure 3

CT images in the transverse plane during the basal (a), the arterial (b) and portal (c) phases show a large mass developed between the second portion of the duodenum and the pancreatic head (arrowhead). This panNEN is associated with a dilation of the intrahepatic biliary tree (d), common bile duct (e) and main pancreatic ductal (f) (arrows). Somatostatin Receptor Scintigraphy with ¹¹¹-pentetrotide shows high uptake of somatostatin analogue in pancreatic lesion (g–i).

Figure 4

Small functioning pancreatic neuroendocrine tumor. T2-weighted MR image (a) shows a small lesion with well-circumscribed margin and high signal intensity (arrow). On T1W image, the lesion appears hypo-intense within the surrounding hyperintense pancreatic parenchyma (b). On contrast enhancement sequences during the arterial (c) and portal (d) phases, the lesion shows hyper-enhancement (arrow). On DWI (e) and ADC map (f), the lesion shows a clearly restrictive pattern.

Figure 5

CT images (a–c) show a hyper-enhancing pancreatic nodule in the body/tail of the organ (arrows) well depicted on the coronal (d) and sagittal (e) reconstruction too. The 68-Ga-DOTATOC PET/CT (f) shows focal uptake in the pancreatic lesion.