[A Case of Extrahepatic Bile Duct Carcinoid Tumor Involving Diagnostic Difficulties]

A patient in his 60s had undergone laparoscopic anterior resection for the treatment of carcinoma of the rectum in February 2016. Histopathologic examination revealed the lesion as a pT2(MP)n(-)M0, fStage Ⅰrectal cancer. One year post-surgery, contrast-enhanced computed tomography(CT)revealed enhancement of parts of the intrapancreatic distal bile ducts. Magnetic resonance cholangiopancreatography(MRCP)showed filling defects at the same site. Magnetic resonance imaging( MRI)with an endorectal coil(ERC)was then performed to identify reproducible bile duct filling defects. Neither cytology nor biopsy yielded any findings that definitely indicated malignancy. Intraductal ultrasonography(IDUS)led to the suspicion of a nonepithelial tumor or an enlarged lymph node. Repeated biopsies via ERC were performed based on the absence of evidence of malignancy and revealed the presence of some atypical cells within the lesions. Although no definitive diagnosis could be made, the patient was scheduled for surgery in June 2017 after obtaining his consent. Upon taping of the common bile duct during surgery, a tumor was palpable on the dorsal aspect of the pancreas. The bile duct tumor was completely excised and submitted for intraoperative diagnosis; the pancreatic dorsal aspect appeared to be totally split. There was no evidence of atypia in the neoplasm, which was therefore considered to be benign; however, malignancy could not be completely ruled out because the patient had presented with elevated serum levels of carbohydrate antigen(CA)19-9 once before the operation. After intraoperative consultation with the patient's family members, who were reluctant to provide consent for pancreaticoduodenectomy, we completed the operation with resection of the bile duct tumor, followed by choledochojejunostomy. The tumor was found to be chromogranin A(+), cluster of differentiation(CD)56(+/-), CA19-9(+, solely ductal structure), carcinoembryonic antigen(CEA)(+, solely ductal structure), and intranuclear p53(-), with an MIB- 1 index of<2%. With regard to neuroendocrine markers, a region that could potentially have been a carcinoid tumor, based on the findings on hematoxylin and eosin(HE)staining, and a lumenized superficial region showed positivity in toto. Therefore, the lesion as a whole was diagnosed as a G1 carcinoid neuroendocrine tumor(NET). However, the superficial lumenized layer was positive for both CA19-9 and CEA; therefore, the tumor was thought to concurrently have epithelial characteristics. The lateral stumpwas negative, while the status of the ablated region remained unclear. After discussing the histopathologic examination results with the patient and his family members, the patient's follow-upwas decided to consist of periodic checkups without any further surgical intervention. The patient has since remained free of recurrence. Carcinoid tumor of the bile duct is extremely rare but should be considered in cases involving bile duct tumors that show enhancement on imaging prior to surgery and for which no definitive diagnosis can be established despite repeated biopsy explorations.