Neuroendocrine tumors constitute a specific histological pattern of tumors, and they were first described by Lubarsch in 1888. To this date, its origin is still unclear. It has been suggested that inflammation causes metaplasia of Kulchitsky's cells, therefore causing their malignant potential. [4]

Common bile duct [CBD] tumors represent less than 2% of all cancers, usually cholangiocarcinomas [80%]. Neuroendocrine tumors of the bile ducts account only for 0.2% to 2.0% of all gastrointestinal NET [4]. CBD is the most common location for extrahepatic carcinoid tumors, followed by a perihilar duct, cystic duct, and common hepatic duct [4,6]. Gallstones and choledochal cyst von Hippel-Lindau syndrome, multiple endocrine neoplasia [MEN-I] syndrome, or the Zollinger-Ellison syndrome have been investigated as a risk factor for the disease [7].

Our patient had symptoms suggestive of obstructive jaundice, resembling most of the literature. Obstructive jaundice, biliary colic, and pruritus represent the most documented symptoms. Patients with obstructive jaundice are investigated with imaging and brush cytology, and no specific pathology could be found. This is further augmented in neuroendocrine tumors because of the submucosal location of the pathology, which yields a high false-negative result of the cytology [5].

To this date, 150 cases of extrahepatic biliary NET have been reported. Since the first case described in 1959, only 4 cases had a preoperative diagnosis of carcinoid tumors [5.1%], with most cases being diagnosed intra-operatively or even postoperatively on the histopathology report like our case [1]. This is due to the absence of hormonal and serum markers on preoperative investigations, in addition to the submucosal location of the tumors as described earlier. However, some authors reported chromogranin, somatostatin, serotonin, and gastrin to be high in these patients [2].

Several reports described some characteristics to differentiate cholangiocarcinoma from NET based on history [8]. Other reports suggested a differentiation based on imaging. NET has a well-circumscribed wall enhancing on arterial phase on CT scan with a polyp-like appearance of a small size, which may distinguish it from cholangiocarcinoma, which usually has a mass obstructing the lumen with hepatic metastasis evident on the liver [6,9].

CT scan, MRCP, and ERCP are the investigation of choice for obstructive jaundice cases. NETs have a specific feature of somatostatin receptors. As a result, DOTA-TATE, DOTATOC, and DOTANOC scans can visualize the tumor. Unfortunately, this is only valid in metastatic disease [7]. Moreover, Positron emission tomography (PET)/CT has no benefit in detecting these tumors [6]. Since our patient had a low-grade, well-differentiated tumor, a DOTA scan was not done.

Complete surgical resection with excision of the extrahepatic bile ducts and portal lymphadenectomy in addition to Roux-en-Y hepaticojejunostomy or even pancreaticoduodenectomy for distal CBD neuroendocrine tumors gives sufficient treatment in the majority of cases [4,7].

The role of adjuvant chemotherapy is still questionable about NETs, as most authors could not describe any survival benefits [4]. In the minority of cases, when a proven preoperative diagnosis of NET is found, Hazama et al. suggested that if there is a biopsy-proven preoperative diagnosis of NEC, preoperative chemotherapy will improve prognosis compared to surgery alone or surgery with adjuvant chemotherapy [5].

Size of the tumor, presence of lymphovascular invasion, and the quantitative assessment of Ki-67 reactive cells, Mitosis index, together with tumor differentiation, and grade help to determine prognosis, although no absolute criteria for determining the malignant potential of extrahepatic NETs have been published to this date; generally, they have a 10-year survival of 80% [7]. In his report of 47 patients, Lee WJ et al. demonstrated that patients with ampulla of Vater NET have a better prognosis and earlier diagnosis than biliary tree NET [10].

Only 40% of patients with NET have hepatic metastases at diagnosis, with the liver being the most affected site [11]. Safwan M et al. reported that serum levels of CgA correlate significantly with metastatic disease, and it is beneficial for recording the recurrence of the disease [8]. In such circumstances, chemoembolization and alcohol-based embolization, together with high-frequency ablation, can be utilized with a successful outcome [12].

This study has multiple limitations; they include a short period of follow-up with clinic visits for one year only, and a DOTA scan was not done because the histopathology showed a low-grade, well-differentiated tumor, and it might have a role in the evaluation of metastasis.