Imaging of pancreatic neuroendocrine tumors: recent advances, current status, and controversies

Abstract

Recently, there have been a number of advances in imaging pancreatic neuroendocrine tumors (panNETs), as well as other neuroendocrine tumors (NETs), which have had a profound effect on the management and treatment of these patients, but in some cases are also associated with controversies. Areas covered: These advances are the result of numerous studies attempting to better define the roles of both cross-sectional imaging, endoscopic ultrasound, with or without fine-needle aspiration, and molecular imaging in both sporadic and inherited panNET syndromes; the increased attempt to develop imaging parameters that correlate with tumor classification or have prognostic value; the rapidly increasing use of molecular imaging in these tumors and the attempt to develop imaging parameters that correlate with treatment/outcome results. Each of these areas and the associated controversies are reviewed. Expert commentary: There have been numerous advances in all aspects of the imaging of panNETs, as well as other NETs, in the last few years. The advances are leading to expanded roles of imaging in the management of these patients and the results being seen in panNETs/GI-NETs with these newer techniques are already being used in more common tumors.

Keywords: CT scan; MEN1; MRI; Neuroendocrine tumor; gastrinoma; imaging; insulinoma; somatostatin receptor imaging.

Figure 1.

Algorithm of imaging for the management/treatment of panNET ¹ Diagnosis based on histopathological findings in NF-panNET, and hormone function tests in F-panNET (see section 2). ² Sporadic or inherited panNETs frequently managed differently (see section 1). ^{3 68}Ga PET/CT allows whole body assessment of disease extent and is more sensitive than cross-sectional imaging (see section 7.C). ⁴ Sensitivity of ⁶⁸Ga-DOTA-SSA PET/CT in insulinomas may be low, due to the low expression/absence of somatostatin receptor subtype 2. In MEN1, neither somatostatin receptor imaging nor cross-sectional imaging identify which imaged NET is functional. Therefore, GLP-1R, EUS-FNA or insulin gradient may be helpful (see section 11). ⁵ If resected panNET is cured but is G3, which is uncommon, then follow as G1/G2 category. ^{6 18}F-FDG PET/CT can identify aggressive NETs (see section 7.D). CT, computed tomography; EUS-FNA, endoscopic ultrasound with fine needle aspiration; F, functioning; FDG, fluorodeoxyglucose; G1/2/3, grade 1/2/3 (according to the WHO classification system); GI, gastrointestinal; GLP-1R, Glucagon-like Peptide 1 receptor; MEN1, multiple endocrine neoplasia-type 1; MRI, magnetic resonance imaging; NF, non-functioning; panNET, pancreatic neuroendocrine tumor; PET, positron emission tomography; PRRT, peptide receptor radionuclide therapy; SSA, somatostatin analogue; US, ultrasonography; VHL, Von Hippel Lindau Disease.