SAT-LB059 NET or NOT: Physiological Uptake in Pancreatic Head on Somatostatin Receptor Based Imaging

Abstract

Introduction Neuroendocrine tumors (NETs) are neoplasms that can arise from the neuroendocrine cells distributed widely throughout the body. Majority of NETs overexpress somatostatin receptors (SSTR) on their cell surface. This biologic characteristic is exploited in the SSTR-based imaging such as 111 In octreotide scintigraphy and 68 Ga DOTATATE positron emission tomography (PET)/CT. These modalities are currently considered standard for initial evaluation of suspected NETs. Although highly sensitive and specific, recent reports demonstrate a concerning incidence of “false-positive” physiologic uptake of these tracers in the pancreatic head - a confounding common site of NET involvement. Case report: A 78 year-old woman presented to clinic with a year-long history of diarrhea. Serum vasoactive intestinal peptide (VIP) levels were slightly elevated at 134.2 pg/mL. CT showed a mildly enhancing 2.5x1.8x2.8 cm area in the pancreatic uncinate process which corresponded to moderate focal uptake with 68 Ga DOTATATE PET/CT. A presumptive diagnosis of NET was made, and the patient was scheduled to undergo Whipple’s surgery. She sought a second opinion at our institution. A subsequent MRI showed no lesion in the uncinate process and the patient’s surgery was deferred. Thereafter, her VIP levels spontaneously normalized. Endoscopic ultrasound (EUS) with fine needle aspiration cytology of the uncinate process showed normal pancreatic acini with no evidence of NET. Conclusion Conspicuous physiological uptake has been reported in the pancreatic head on 16-70% of 68 Ga DOTATATE or 68 Ga DOTANOC PET/CT scans, and 26% of the 111 In octreotide scintigraphy scans. 1 Image-based quantitative attempts to distinguish physiologic from pathologic uptake using SUVmax have rendered mixed results. When evaluating SSTR-based imaging uptake in the pancreatic head, patients can benefit from a higher index of suspicion of false positive uptake. Such cases require additional confirmation by means such as MRI or EUS. The patient described above also had mild contrast enhancement on CT, but an MRI didn’t show any corresponding lesion. Because of potential morbidity and mortality related to false positive uptake, a systematic review with evidence-based recommendations for imaging may benefit patient care. 1. Brabander T, et al. Physiological Uptake in the Pancreatic Head on Somatostatin Receptor Scintigraphy Using [111In-DTPA]Octreotide: Incidence and Mechanism. Clin Nucl Med 2017;42:15-9. Unless otherwise noted, all abstracts presented at ENDO are embargoed until the date and time of presentation. For oral presentations, the abstracts are embargoed until the session begins. Abstracts presented at a news conference are embargoed until the date and time of the news conference. The Endocrine Society reserv...