Ampullary Neuroendocrine tumors (ANETs), formerly carcinoids of the ampulla of Vater, are extremely rare neuroendocrine tumors accounting for less than 0.3% of gastrointestinal carcinoids [1] . ANETs are neoplasms that arise from cells of the endocrine and nervous systems possessing secretory granules and often producing biogenic amines and peptide hormones [2] . According to the most recent data from the Surveillance, Epidemiology and End-Results (SEER) of the National Cancer Institute only 139 cases of ANET (82 low and 57 highgrade) have been reported worldwide [3] making robust epidemiologic factors difficult to ascertain. With such little consensus available, management of ANET can pose a challenge for even the seasoned gastric surgeon.

Pancreaticoduodenectomy is often recommended as the treatment of choice for tumors of any size without distant spread. However procedures like local excision and endoscopic resections have also been successfully attempted, especially for ANET less than 2 cm size [4] [5] . Here, we demonstrate a case of low-grade, well-differentiated, ANET in a young patient who presented with non-specific abdominal pain who underwent a successful local resection at our institution followed by a review of the literature.

A 21-year-old Burmese male immigrant was referred for evaluation of a 6-year history of non-specific upper abdominal pain that had worsened 8 months prior to presentation. He denied any prior history of nausea, vomiting, flushing, diarrhea or jaundice. He did not drink alcohol or take any medications and had no significant past medical or family history. Physical exam was notable for epigastric and right upper quadrant tenderness. There were no palpable abdominal masses or adenopathy. Skin was negative for café au lait spots and jaundice.

Initial lab workup including a complete blood count, liver function test, urine analysis, and serum electrolytes were within normal limits. A right upper quadrant ultrasonography revealed a thickened gallbladder wall without obvious cholelithiasis. He was therefore scheduled for a Hepatobiliary Iminodiacetic acid (HIDA) scan which showed normal gallbladder visualization, contraction and motility on cholecystokinin stimulation and the absence of obstruction. An upper endoscopy was performed at follow up appointment. This study revealed a normal exam up to the level of the second part of the duodenum. Within the ampulla however, a single large nodule was visualized at the area of the major papilla with normal appearing overlying mucosa (Figure 1).

Subsequent endoscopic ultrasonography confirmed the presence of a hypoechoic heterogenous mass that measured 13.2 mm in maximal cross-sectional diameter with sonographic evidence of invasion into the deep mucosa without involvement of the pancreas (Figure 2). Intraprocedural fine-needle aspiration was undertaken. Biopsy results showed scattered loosely cohesive fragments and individual cells with uniform, rounded nuclei and speckled chromatin suggestive of a well differentiated neuroendocrine tumor (Figure 3). A subsequent computed tomography with intravenous contrast was obtained which was negative for both masses and metastatic disease. As well, serum chromogranin A (2.4 ng/mL, norm 1.9 - 15 ng/mL) and gastrin (175 pg/mL, norm 10 - 200 pg/mL) levels were acquired along with a 24-hour urine HIAA level (2.5 mg, norm < 6 mg/24hr) which were all within normal limits. Next, an octreotide scan was obtained over a 3-day period that yielded no abnormal findings. Magnetic resonance cholangiopancreatography showed findings suggesting a 13.2 mm polypoidmass which projected into the duodenal lumen on thin slices. Common bile and pancreatic duct dilatation were absent on our study, measured 5 mm and 2 mm respectively. Additionally, no abnormalities of the liver, pancreas or gallbladder were seen.

A resection of the ampulla of Vater was planned and performed with sphincteroplasty and cholecystectomy.

Surgery revealed a 13.2 mm mass at the level of the ampulla of Vater. Pathology confirmed well-differentiated neuroendocrine tumor (WHO grade 1) with clear margins of 2 mm, with no lymphvascular and perinueral invasion. Further characterization included the presence of psammoma calcifications, positive immunoreactivity for somatostatin, CD8/18, chromogranin A, synaptophysin, and focal positivity of s100 and Ki67 (<1%). Of note, the sample was negative for c-KIT, gastrin, CD34 and CD68.

The patient made an uneventful recovery and was discharged home on post-operative day four. He is currently disease free at 24 months from his date of surgery. He returns to our department for follow up on a regular basis.

Historically, any and all neuroendocrine tumors that arose within the gastrointestinal tract were called carcinoid tumors. However, recently this terminology has been abandoned and now the term carcinoid is reserved for only low-grade, well differentiated, neuroendocrine tumors. ANET are extremely rare and account for less then 1% of all gastrointestinal neuroendocrine tumors and less than 2% of all tumors of the ampullary region [3] [6] . Carcinoids involving the ampulla of Vater can be derived from cell types of the duodenum, common bile duct or the pancreas. Two main categories of ANET exist: low-grade ANET and high-grade ANET which are distinguished on the basis of their proliferative rates assessed by amount of necrosis, mitotic figures per high power field or Ki67 labeling index [7] [8] .

The SEER database reported 76 males and 63 females out of a total of 139 cases of ANET, with an average age at presentation of 61 years for low grade and 62 years for high-grade neuroendocrine tumors [3] .

ANET does not show any sex predilection although data suggests that females typically present younger than their male counterparts. To our knowledge this patient is the youngest case in the medical literature to be diagnosed with this tumor.

ANETs are rare GI tumors but nevertheless should be included in the differential list for recurrent abdominal pain of unknown cause. Though pancreatiduodenectomy has been standard practice, there is increasing evidence that local resection could be an alternative treatment modality with much less morbidity—an important consideration when deciding management options in younger patients.