[A Case of Extrahepatic Biliary Resection for Primary Neuroendocrine Tumor of the Gallbladder(NET G1)].

In this report, we described a case of an extremely rare primary neuroendocrine tumor of the gallbladder, which corresponds to NET G1 according to the WHO classification. The patient was a 71 year-old man. He was diagnosed as dilated common bile duct by abdominal ultrasound a medical checkup. The patient was referred to our hospital because of a contrast-enhancing mass in the neck of the gallbladder on CT. EUS was performed, and a substantial tumor with contrast effect was observed from the neck to the duct of the gallbladder. The preoperative diagnosis was gallbladder cancer of cT3N0M0, Stage ⅢA. The tumor was suspected of invading the common bile duct. As a result, the operation was extrahepatic biliary resection and biliary reconstruction. A gross examination of the explanted specimen revealed an 8 mm sized cauliflower-like polypoid lesion on the neck of the gallbladder. Histopathologically, the lesion showed hyperplastic polyp-like lesions with substantial, cord-like, tubular, ribbon-like, or individual cellular growths in the intrinsic layer of the mucosa. Immunostaining was diffusely positive for chromogranin A, synaptophysin, and INSM1. Based on the histology of the tumor and the fact that it was Ki-67 positive(1%)with no fission pattern, a diagnosis of gallbladder NET G1, pT1aN0M0, Stage ⅠA was made.