Neuroendocrine Tumor of the Cystic Duct: A Rare and Incidental Diagnosis.

Neuroendocrine tumors (NETs), also known as carcinoid tumors of the extrahepatic biliary tree, are extremely rare malignancies and account for 0.2% to 2% of all carcinoids of the gastrointestinal tract. The most common sites include NET in the common bile duct (CBD), followed by the perihilar region, cystic duct, and common hepatic duct (CHD). A review of the literature showed only eight cases of NETs of the cystic duct and we, hereby, present the ninth case of NET of the cystic duct in a 50-year-old woman. This was discovered incidentally after she underwent a laparoscopic cholecystectomy for her symptomatic gallbladder stones. The etiology is not known but the NETs are thought to arise from argentaffin cells (Kulchitsky cells) in the gastrointestinal tract or respiratory tract. It is possible that the rarity of these in this region may be explained by the very limited number of Kulchitsky cells there. Most of the patients are clinically asymptomatic, and the diagnosis is mostly made during surgery performed for other indications. Therefore, early recognition should be sought by differentiating the primary duct carcinoma of the bile or the cystic duct, if suspected or shown on the imaging studies because of the different therapeutic options and prognosis.