Abstract
A 69-year-old woman with dorsal pain visited our hospital, and underwent upper gastrointenstinal endoscopy, leading to the discovery of a submucosal tumor (SMT) measuring about 10 mm in diameter, which was located at the anterior wall of the duodenal bulb adjacent to the pyloric ring. The biopsy specimen showed positive expressions for neuroendocrine markers on immunostaining, resulting in a diagnosis of neuroendocrine tumor (NET). Based on assessment of the proliferative activity (mitotic count, <2 per 10 high power fields (HPF) and/or ≤2% Ki-67 index), the SMT was finally diagnosed as Grade 1 (G1). This case was considered an indication for limited surgery because NET-G1 that is not greater than 10 mm and not proliferating beyond the submucosal layer is generally estimated to be unlikely to metastasize to a lymph node. Thus, the patient underwent distal gastrectomy including the duodenal bulb. Histopathological findings showed a well-circumscribed tumor measuring 8 mm located in the submucosal layer．The presence of metastasis was confirmed in one of the subpyloric lymph nodes. Unexpectedly, an analysis of 21 duodenal NETs gathered from Japanese case reports showed that 3 cases had nodal metastasis in the case of either G1 or tumors with a diameter up to 10 mm. The potential risk of nodal metastasis should be recognized when treating duodenal NETs, even in cases of fulfilling all the condition of low-risk factors for nodal metastasis.
