The term carcinoid has been replaced with NET based on the development of diagnostic tools and immunochemistry. Recently, NETs have been reclassified within the spectrum of gastroenteropancreatic-neuroendocrine tumours (GEP-NETs) . However, the term "classical carcinoid" is used synonymously with the term serotonin-producing GEP-NETs . A classical carcinoid tumor is usually still referred to as a carcinoid tumor. The incidence of gastrointestinal carcinoids is 1.6-2.0 cases per 100, 000 persons per year , but the true prevalence may be higher 
Although more than 70 cases involving carcinoid tumors of the major papilla have been reported , only 8 cases of carcinoid tumors involving the minor papilla have been reported [1–8]. Carcinoids and endocrine cell micronests (ECMs) in the minor papilla occur more frequently than generally thought. In a single surgical specimens and autopsy study, the incidence of carcinoids and neoplastic ECMs of the minor papilla could reach 10%. Furthermore, carcinoids in the minor papilla are twice as common as carcinoids of the major papilla, and neoplastic ECMs of the minor papilla are found five times as often . This discrepancy may be explained by the fact that tumors of the major papilla are more likely to develop symptoms, such as jaundice or abdominal pain, due to ampullary obstruction, whereas patients with minor papillary tumors usually remain asymptomatic because there is no biliary or pancreatic obstruction.
Carcinoid tumors of the minor papilla of the duodenum are very difficult to diagnose because they are usually small in size and located at the submucosal area, and they are frequently asymptomatic  and rarely accompanied with endocrine manifestations . In our case, although the size of the carcinoid tumor was small and the tumor was hormonally inactive, the concomitant pancreas divisum led to an early diagnosis because obstruction of the minor papilla due to the carcinoid tumor caused recurrent abdominal pain and resulted in dilatation of the main pancreatic duct. Of the eight reported cases of carcinoid tumors involving the minor papilla in the literature, five cases have been associated with pancreas divisum and presented with recurrent abdominal pain or pancreatitis [3–7].
The endoscopic features of carcinoid tumors are small, round, sessile, or polypoid lesions with a smooth surface. Carcinoid tumors usually have normal overlying mucosa and seldom ulcerate . An EUS may be useful for the diagnosis of carcinoids and evaluation of regional lymph node metastasis, but CT or MRI scans are not helpful in most cases because of the small size. Carcinoid tumors usually appear as a homogenous, well-demarcated, and mildly hypoechoic or isoechoic mass that arises from the second layer on EUS. In addition, EUS can define the size, tumor invasion, and regional lymph node metastasis . The pre-operative diagnosis of carcinoid tumors of the duodenal papillae is largely dependent upon endoscopic biopsy. However, a correct diagnosis is made in only 14% of the patients13 because the tumors are usually submucosal in location . As in our case, multiple deep biopsies are required to enhance the tissue diagnosis.
Though endoscopic resection may be an alternative to surgical resection [8, 17], radical surgery is usually recommended as the treatment of ampullary carcinoid tumors [13, 18] because carcinoid tumors of this area appear to have more aggressive biology with presence of metastasis in approximately 50% of the cases, irrespective of the size of the primary tumor or mitotic activity [13, 19, 20]. In our case, despite the tumor being 1 cm in diameter, the histologic examination revealed duodenal and vascular invasion and metastasis to the regional lymph nodes. In conclusion, carcinoid tumors of the minor papilla are very rarely found, but the true incidence might be much higher, and the tumors frequently have aggressive behavior. Carcinoid tumors of the minor papilla should be included in the differential diagnosis of recurrent abdominal pain or pancreatitis of unknown cause.