Functional and Radiological Imaging of Neuroendocrine Neoplasms

Imaging of neuroendocrine neoplasms (NENs) is extremely rich and varied. Conventional techniques of morphological imaging (ultrasound, CT, MRI) are complementary to other imaging techniques such as endoscopic explorations and functional imaging using radiopharmaceutical imaging techniques. NENs have very distinct functional characteristics, which make them ideal targets for functional molecular imaging. Functional imaging plays a crucial role in the assessment of initial tumor distribution (staging), disease assessment after therapy (restaging), disease follow-up, and planning for somatostatin receptor (SSTR) 2-based radiopeptide treatment. Other tracers, such as 123I-metaiodobenzylguanidine (123I-MIBG) scintigraphy or 18F-DOPA (dihydroxyphenylalanine) and the SSTR2-antagonist (NODAGA-JR11) PET/CT have been developed for specific indications or to gain sensitivity and specificity. The more aggressive, less differentiated neuroendocrine carcinomas tend to have less SSTR2 receptor expression, and the tumor cell metabolism shifts toward anaerobic glycolysis. In these patients, receptor-based imaging should be complemented or replaced by metabolic 18F-FDG (18F-fluorodeoxyglucose) PET/CT. The continuum from well-differentiated neuroendocrine tumor to a more aggressive neuroendocrine carcinoma makes functional imaging sometimes challenging