neuroendocrine tumors ( nets ) are neoplasms that develop from the neuroendocrine cells of diffuse neuroendocrine systems . gastric nets are rare lesions , representing approximately 7  % of all nets and less than 1  % of all stomach neoplasms 1 . according to the histologic classification of tumors developed by the world health organization in 2010 , nets are classified as g1 to g3 based on the rate of mitosis and the ki-67 labeling index ; net g1 is synonymously referred to as a carcinoid 2 
 3 . the prevalence of nets is relatively high , as many nets are slow - growing or of uncertain malignant potential , and even malignant nets are associated with prolonged survival 4 . gastric nets usually have the endoscopic appearance of a submucosal tumor , as they grow from deep within the mucosal layers 5 
 6 . herein , we report a case of an 87-year - old man with a pedunculated gastric net treated by endoscopic surgery . he had a history of hypertension and was taking medication to lower blood pressure ( enalapril maleate 2.5  mg / day , amlodipine besilate 5  mg / day ) . we performed gastroendoscopy to search for disease of the gastrointestinal tract and found a polypoid lesion in the stomach . the gastric lesion was a pedunculated polyp with a reddish head ( fig .  1 , fig .  2 ) . the borderline of epithelial change between the head and the stalk region was unclear endoscopically . observation with a narrow band image system revealed dilated vessels at the head of the lesion . because the stalk of the lesion was thick and rich in inflammatory change ( fig .  1 , fig . 2 ) , we were concerned that if the polyp was neoplastic , the lesion could have potentially invaded the stalk . we were also concerned that the lesion could potentially have had a thick tumor - feeding blood vessel , especially a thick feeding artery , in its stalk . c and d : view of the tumor looking up from the anal side . a white light image of the carcinoid tumor located posterior to the corpus b narrow band image showing a bulging area ( yellow arrow ) on the tumor stalk . c white light image of the tumor showing its reddish head compared with the stalk . a white light image showing that the head portion was reddish and had an eroded mucosal area . b narrow band image showing dilated vessels on the head portion of the tumor ; in some areas the vessels were unclear because of erosion caused by inflammation . after spraying with indigo carmine , c the head portion of the tumor was coated with mucus , especially in the eroded area , and the surface of the tumor was relatively smooth . d while there was a color difference between the head and the stalk , the tumor appeared to form a seamless surface . from this view , the bulging area of the tumor stalk ( yellow arrow ) was more visible . because the patient and his family hoped to have the gastric lesion resected endoscopically , we planned to perform endoscopic treatment for the polypoid lesion in the stomach . we decided to perform endoscopic submucosal dissection ( esd ) , which would enable us to resect the lesion en - bloc and also allow us to confirm blood vessels as needed during procedure . the tumor cells had a solid structural appearance from the deep mucosal layer to the submucosal layer . immunostaining examinations were conducted , and the lesion was found to be positive for chromogranin a and synaptophysin ( fig .  4 ) . although pseudopyloric glands were not observed , endocrine cell micronests ( ecms ) were observed . the ki-67 positive index was less than 2  % . thus , the lesion was finally diagnosed pathologically as an net g1 , pm - psm , ly0(d2    40 ) , v0(em ) , phm0 , pvm0 ( fig .  4 ) . tissue cross - sections stained with hematoxylin & eosin . a loupe image of the carcinoid . the head of the tumor had a mucosal deficit caused by biopsy ( blue arrow ) . the bulging area is again apparent ; the loupe image shows that this was caused by the carcinoid mass ( green arrow ) . c small tumor cells with small rounded or oval nuclei formed cord - like structures . d and e : in the stalk of the tumor there were carcinoid tumor cells forming honeycombed structures . e immunohistochemistry for synaptophysin showed endocrine cell micronests in the mucosa surrounding the carcinoid tumor . the serum gastrin level evaluated 9 months after the patient stopped taking a proton pump inhibitor was elevated at 552  pg / ml ( normal range : 42    200  pg / ml ) . we biopsied the mucosa of the gastric antrum , and found no evidence of overexpression of g cells pathologically . chronic gastritis was widely seen endoscopically , and the helicobacter pylori antibody titer was markedly increased at 24.3  u / ml ( normal range : <  10  u / ml ) . the serum level of vitamin b12 was 879  pg / ml ( normal range : 233 914  pg / ml ) , and serotonin was 154.5  ng / ml ( normal range : 81    262  ng / ml ) . the results for anti - parietal cell antibody and anti - intrinsic factor were negative . after extended consultation with the patient and his family , who preferred to avoid surgical treatment , we decided on a strategy of close monitoring without additional surgical treatment . we checked the condition of the patient periodically , and computed tomography and gastroendoscopy showed no evidence of local or other metastatic recurrences . one year after the esd was performed , the patient was in good condition without carcinoid tumor recurrence . gastric nets are classified into 3 subtypes : type i lesions arising in patients with chronic atrophic gastritis , including autoimmune gastritis and h. pylori - associated atrophic gastritis ; type ii lesions associated with gastrin - producing neoplasms in patients with multiple endocrine neoplasia or zollinger  ellison syndrome ; and type iii gastric lesions , which are sporadic carcinoids without specific background factors 7 . in this case , the disease was negative for both anti - parietal cell antibody and anti - intrinsic factor . however , the gastric mucosa was highly atrophic , with h. pylori infection , elevated gastrin , and the presence of ecms . the aim in treating gastric net should always be to maintain good quality of life for as long as possible 4 . carcinoids generally have an excellent prognosis , especially type i gastric carcinoid tumors , which have low malignant potential and low frequency of metastasis 4 
 7 
 8 . patients managed by lesion resection and endoscopic follow - up have a 100  % survival rate when the lesions are confined to the submucosa and there are no metastases during observation 8 . in many cases surveillance only is appropriate , although limited surgery with endoscopic polypectomy and/or antrectomy may be preferable 4 .   in the current case esd is reportedly more feasible than endoscopic mucosal resection for removal of type i gastric carcinoid 7 . complete histologic resection was performed by esd in the current case , and no complications such as bleeding or gastric perforation occurred during or after endoscopic treatment . if polypectomy had been performed for this lesion , the cut edge of the tumor would have been positive for neoplasia , because the carcinoid tumor had invaded to the level of the submucosal layer in the stalk of the polyp . pedunculated carcinoid tumor is very rare , and there are only a few previously reported cases 9 
 10 . however , the previous reports did not contain detailed endoscopic findings or images of pedunculated carcinoid tumor . in this report , we describe detailed endoscopic findings of pedunculated carcinoid tumor with endoscopic images ( fig .  1 , fig .  2 ) . as this was our first case of pedunculated gastric carcinoid tumor , we did not initially consider the lesion a carcinoid tumor . this case shows that it is difficult to immediately diagnose a net based on endoscopic findings . based on the endoscopic findings in the current case , we initially believed that the lesion was potentially a hyperplastic polyp or neoplastic lesion with strong inflammatory changes on its surface . fisher reported that a pedunculated gastric carcinoid develops because peristalsis causes formation of a pedicle and a pedunculated polyp 9 . peristalsis could misalign the carcinoid tumor and the gastric muscle layer , and cause the tumor to extend to the submucosal layer toward the inner cavity . because gastric carcinoids are slowly progressive tumors , they change shape slowly over time from a semi - pedunculated to a pedunculated polyp . in the current case , because the patient had never had an endoscopic examination , the gastric carcinoid grew slowly and gradually formed into a pedunculated polyp . furthermore , the tumor mass was located in the stalk , which was recognizable as a bulging area of the tumor stalk ( fig .  1 , fig . 2 ) , and served as a prop by forming a solid part of the stalk . because our institute ( kakunodate municipal hospital ) did not have an ultrasonographic endoscope , we were not able to perform endoscopic ultrasonography ( eus ) of the lesion , which might have provided more detailed information regarding the submucosal layer . in cases of pedunculated gastric lesion where the lesion originates from the submucosal layer or the lesion may potentially have invaded the submucosal layer , eus provides valuable information that helps in selecting the treatment strategy .
background and study aims : gastric neuroendocrine tumors ( nets ) are rare lesions that develop from neuroendocrine cells . 
 nets are classified into 3 types based on the rate of mitosis and ki-67 labeling index ; the net g1 type is synonymously referred to as carcinoid . 
 gastric nets are usually discovered as submucosal tumors during upper gastrointestinal endoscopic examination . 
 this study reports a rare case of pedunculated gastric net . 
 the lesion was found as a result of gastroendoscopy . 
 the gastric lesion was a pedunculated polyp with a reddish head . 
 we performed endoscopic submucosal dissection and an en - bloc resection of the gastric lesion . 
 the resected specimen was evaluated histopathologically and diagnosed as a carcinoid ( net g1 ) .