Incidental Detection of a Well-Differentiated Neuroendocrine Tumor of the Gallbladder: A Case Report.

Neuroendocrine tumors (NETs) of the gallbladder are uncommon and are often difficult to diagnose preoperatively due to their nonspecific clinical and imaging findings. A 39-year-old man presented with right upper quadrant abdominal pain without fever, jaundice, or signs of peritoneal irritation. Abdominal ultrasonography revealed a 9 mm polypoid lesion in the neck of the gallbladder, and contrast-enhanced computed tomography demonstrated an 8 mm slightly enhancing lesion with gallbladder wall thickening consistent with cholecystitis. Blood tests showed no elevation of inflammatory markers. Although initial observation was considered, the patient experienced recurrent biliary colic-like pain. We suspected that the polyp located in the gallbladder neck was causing intermittent obstruction of the cystic duct, leading to these symptoms. Laparoscopic cholecystectomy was performed under a preoperative diagnosis of a benign gallbladder polyp. Histopathological examination showed uniform proliferation of tumor cells confined to the mucosa with occasional glandular structures in the background of chronic cholecystitis. Immunohistochemical analysis revealed positivity for neuroendocrine markers (chromogranin A, synaptophysin, and CD56) with a Ki-67 labeling index of <1%. Based on these findings, the tumor was diagnosed as a well-differentiated NET of the gallbladder. We experienced a case of well-differentiated NET incidentally diagnosed after laparoscopic cholecystectomy for a gallbladder polyp. Since cases of early-stage gallbladder NETs are rare, their clinical behavior and long-term prognosis remain poorly understood. This case underscores the need for continued case accumulation and careful postoperative follow-up to establish appropriate management strategies for this rare entity.