Polypoid gallbladder neuroendocrine tumor diagnosed as benign polyp before surgery: A case report

Abstract

Gallbladder neuroendocrine tumors (GB-NETs) comprise only 0.5% of all NET cases, and their biology has been incompletely characterized. In the present study we report the case of a 50-year-old male patient with GB-NET who was admitted to Naito Hospital with diarrhea as the main complaint. At initial diagnosis, serum carcinoembryonic antigen (CEA) and carbohydrate antigen 19-9 (CA19-9) levels were within the normal range. Abdominal ultrasonography and contrast-enhanced computed tomography (CT) revealed gallbladder adenomyomatosis and cholecystitis, and an 8-mm pedunculated polypoid lesion was found in the neck of the gallbladder using drip infusion cholecystocholangiog-raphy-CT. As it was considered a benign polyp, laparoscopic cholecystectomy was performed. Pathological examination revealed a polypoid lesion that comprised NET cells with a cord-like or ribbon-like arrangement, and the cells exhibited positive immunostaining for chromogranin A and synapto-physin. In addition, immunohistochemical staining showed a Ki-67 index (i.e., proliferation index) of <1%, and no necrosis or mitotic figures were observed in the background. Based on these observations, we diagnosed the following: GB-NET, G1, 10x12 mm in size and located in the gallbladder neck. According to the World Health Organization 2010 classifica-tion, NET G1 is a well-differentiated tumor, with the tumor cells having a low proliferative potential [Ki-67 index ≤2%; mitotic figure number <2 (/10 HPF)]. It is regarded as a low- to mild-grade malignancy. Low-grade GB-NET occurs relatively rarely, and no clear guidelines have been formulated regarding its surgical treatment, such as minimal surgical excision margins or lymph node dissection. Detailed treatment recom-mendations should be developed after systematic studies of additional cases of GB-NET.