Underwater Endoscopic Resection for the Rare Periampullary Tumor

Composite gangliocytoma/neuroma and neuroendocrine tumors (CoGNETs) are extremely rare periampullary neoplasms composed of neuroendocrine epithelial, Schwannian spindle, and ganglion cells. Although endoscopic papillectomy or surgery have been used to treat ampullary CoGNETs, underwater endoscopic mucosal resection (UEMR) for periampullary lesions has not been previously described. In this study, we present a case of a 53-year-old man referred to our hospital with an incidentally detected subepithelial tumor in the second portion of the duodenum. Endoscopic ultrasound revealed a 13×10-mm homogeneous, hypoechoic, and well-demarcated submucosal mass. UEMR was performed under conscious sedation without submucosal injection, achieving safe en bloc resection within 12 min. Histopathology revealed a 2.0×1.5×1.2-cm lesion composed of mixed neuroendocrine epithelial, Schwannian spindle, and ganglion cells. Immunohistochemical staining was positive for chromogranin A, synaptophysin, CD56, neuron-specific enolase, and S-100, confirming CoGNET with a Ki-67 index of