Intracholecystic Papillary Neoplasm Mimicking High-Grade Dedifferentiation in a Patient With Neuroendocrine Tumor: The Value of Dual-Tracer PET/CT.

A 50-year-old man with weight loss and fatigue was diagnosed with a grade 2 liver-metastatic neuroendocrine tumor (NET). Dual-tracer molecular imaging was performed for staging and characterization. While 18F-FDG PET/CT showed focal high uptake in a gallbladder lesion (SUVmax: 10) and non-FDG-avid liver metastases, 68Ga-DOTATATE PET/CT revealed intense somatostatin receptor expression in the primary pancreatic lesion and liver metastases, but no uptake in the gallbladder. This discordant "flip-flop" pattern typically suggests high-grade dedifferentiation. However, histopathology following cholecystectomy revealed a low-grade intracholecystic papillary neoplasm (ICPN). This case highlights that discordant FDG-positive/SSTR-negative foci in NET patients can represent rare premalignant mimics rather than aggressive tumor biology.