Optimal surgery and lymph node metastasis of duodenal bulbar neuroendocrine neoplasms

•The nodal metastases for duodenal bulbar neuroendocrine neoplasms were examined.•Risk factors were tumor size >15 mm and muscularis propria or deeper invasion.•Stomach-related lymph node metastasis was found in 15.4% even with no risk factors.•Pancreas-related lymph node metastasis was not found in patients negative for both.•45.5% of patients with both risk factors metastasized to the pancreas-related ones.