carcinoid tumors , relatively rare neuroendocrine neoplasms arising from enterochromaffin cells , were first described by lubarsch in 1888 . since 1974 , functional neuroendocrine tumors have been classified according to the major hormones secreted , such as insulinoma , gastrinoma , vipoma , glucagonoma , and somatostatinoma . since the first two case reports of somatostatin - secreting tumors in 1977 , fewer than 200 cases of somatostatinoma have been reported . the pancreas is the most common site of somatostatinoma ( 68% ) , followed by the duodenum ( 19% ) , ampulla of vater ( 3% ) , and small intestine ( 3% ) . typical somatostatinomas are large , solitary , malignant tumors that are often discovered with lymph node or liver metastases at the time of diagnosis . the clinical presentation includes abdominal pain , nausea , obstructive jaundice , and endocrinopathy , such as a somatostatin syndrome . it is caused by excess somatostatin released from the somatostatinoma and consists of the clinical triad of diabetes mellitus , cholelithiasis , and steatorrhea . here , we report a case of a nonfunctional duodenal somatostatinoma and review gastrointestinal somatostatinomas . a 58-year - old man was referred to our hospital for evaluation of a periampullary mass detected on ultrasonography . abdominopelvic computed tomography ( ct ) revealed a 25-mm mass in the medial side wall of the second portion of the duodenum at the level of the ampulla of vater ( fig . 1a ) and a 25-mm ill - defined lowattenuating nodule in the left medial segment of liver ( s4 ) ( fig . the intrahepatic duct , common bile duct ( cbd ) , and pancreatic duct ( pd ) were dilated . the total serum bilirubin was 0.5 mg / dl , and the serum ast / alt was 38/47 the tumor markers ca19 - 9 , carcinoembryonic antigen , and a - fp were all in the normal ranges . his fasting blood sugar was 118 mg / dl , but a glucose tolerance test was normal . endoscopic retrograde cholangiopancreatography ( ercp ) showed an enlarged ampulla of vater covered with a smooth mucosal surface ( fig . 2 ) . however , the orifice was too narrow to insert the scope for a cholangiopancreatogram . endoscopic ultrasonography revealed a well demarcated mass under the duodenal mucosa that compressed the distal lumens of the cbd and pd , and caused dilatation of the proximal cbd and pd ( fig . ten days later , the patient underwent whipple 's operation ( pancreaticoduodenectomy ) , since the tumor was highly suspicious for malignancy at endoscopy . at surgery , a 2.5  2.5-cm enlarged ampulla of vater was found at the second portion of the duodenum ; its surface was smooth and covered with duodenal mucosa . a hepaticojejunostomy was also performed , and all of the enlarged lymph nodes were dissected . the pathological examination showed a 2.3  2.3  2-cm mass located mainly in the duodenal submucosa , abutting the superficial muscle layer of the duodenum ( fig . the tumor was located in the duodenal submucosa and distal cbd , dilating the cbd . a microscopic examination revealed that the tumor consisted of uniform cells arranged in solid nests , cords , and glandular patterns without psammoma bodies ( fig . they were argyrophilic on churukian schenk 's staining , but non - argentaffinic on fontana - masson staining . the 6-month follow - up , abdominopelvic ct showed no recurrent mass and the previous hepatic nodule . a somatostatinoma , a carcinoid tumor arising from enterochromaffin cells , is a relatively rare neuroendocrine tumor ; the pancreas is the most common site of somatostatinomas . somatostatin is a cyclic tetradecapeptide widely distributed in normal human tissues and secreted by the hypothalamus , cerebrum , spinal cord , vagus nerve , and d cells in langerhans islets of the pancreas , stomach , duodenum , and small intestine . somatostatin inhibits numerous endocrine and exocrine secretory hormones , including insulin , cholecystokinin , pancreatic enzymes , and gastrin . nonspecific symptoms such as vague abdominal pain , nausea , weight loss , and altered bowel habits are more common than somatostatin syndrome . they frequently present with abdominal pain , obstructive jaundice , cholelithiasis , vomiting , and abdominal bleeding , rather than typical somatostatin syndrome . in this case , the tumor originated from the duodenum and was smaller than 4 cm . unfortunately , the serum insulin , glucagon , gastrin , somatostatin , and urine 5-hydroxyindoleacetic acid ( 5-hiaa ) levels were not checked . before the exploratory laparotomy the serum somatostatin level is usually elevated in functioning tumors , although duodenal somatostatinomas are usually non - secretory . given the nonspecific symptoms and laboratory findings , microscopic and immunohistochemical studies typically enable a specific diagnosis . the tumor cells are arranged uniformly in trabecular , acinar , ribbon , or cribriform structures . these spherical bodies have been reported in somatostatinomas of the ampulla of vater , and in pancreatic and extrapancreatic somatostatinomas , papillary thyroid cancers , serous ovarian tumors , and meningiomas . most carcinoid tumors stain positively for chromogranin a , neuron - specific enolase , leu-7 , and specific endocrine cell markers . on classical silver staining , 75% to 80% of carcinoid tumors are argyrophilic , while they are seldom argentaffinic . since the pathological findings of our tumor concurred with somatostatinoma , we diagnosed it as a duodenal somatostatinoma . considering its malignant potential , generally , for tumors 1 cm or smaller , endoscopic excision is adequate because of the low incidence of metastasis . for lesions between 1 and 2 cm larger lesions are more aggressive and invasive . tumors larger than 1 cm are likely to invade to deep layer beyond the submucosa   and endoscopic resection can not always remove the tumor completely . the malignant nature of duodenal somatostatinomas and the risk of metastasis increase significantly in tumors larger than 2 cm . for larger tumors ( > 2 cm ) , whipple 's operation with a regional lymphadenectomy should be considered , even if all of the regional lymph nodes are negative in preoperative imaging studies . regardless of the size of the primary tumor , if abnormal lymph nodes are detected , the tumor and all of the regional lymph nodes should be removed . this recommendation is based on the experience with duodenal gastrinomas , for which surgical resection of lymph node appears to improve survival . with liver metastases of neuroendocrine tumors , cytoreductive therapy , such as segmentectomy or lobectomy , multi - agent regimens , such as combinations of streptozocin , fluorouracil , cyclophosphamide , or doxorubicin , produce limited responses in patients with metastatic disease . the 5-year survival rate is 40% in somatostatinomas with liver metastasis , but 100% in tumors without liver or lymph node metastases .
somatostatinomas are rare functioning carcinoid tumors that usually arise in the pancreas and duodenum . 
 they are seldom associated with typical clinical symptoms ; their diagnosis is confirmed only by histological and immunohistochemical studies and the presence of specific hormones . 
 two distinct clinicopathological forms of somatostatinoma exist : duodenal and pancreatic somatostatinomas . 
 clinically , compared to pancreatic somatostatinomas , duodenal somatostatinomas are more often associated with nonspecific symptoms and neurofibromatosis , but less often with somatostatinoma syndrome or metastasis . 
 histologically , duodenal somatostatinomas frequently have psammoma bodies in the tumor cells . 
 we report a case of duodenal somatostatinoma in 58-year - old man with vague epigastric pain and nausea . 
 he did not have diabetes , steatorrhea , or cholelithiasis . 
 abdominal computed tomography showed a 25-mm mass in the duodenum and 25-mm nodule in the liver . 
 endoscopic retrograde cholangiopancreatography showed a duodenal submucosal tumor . 
 although the endoscopic biopsies were free of malignancy , the patient subsequently underwent whipple 's operation for the duodenal mass . 
 examination revealed as a somatostatinoma using a special stain for somatostatin .