The Mesenteric Masquerader: A Rare Primary Neuroendocrine Tumor of the Mesentery.

Primary neuroendocrine tumors (NETs) arising exclusively within the mesentery, without an identifiable gastrointestinal or pancreatic primary, are exceedingly rare and often present with non-specific symptoms, making preoperative diagnosis challenging. We report the case of an 80-year-old female who presented with a six-month history of right-sided abdominal pain and a palpable abdominal mass. Contrast-enhanced computed tomography of the abdomen revealed a well-defined soft tissue lesion measuring 7.1 × 4.4 × 5.3 cm in the right iliac fossa mesentery, with vascular supply from the superior mesenteric artery. The mass was successfully excised laparoscopically en masse. Histopathological examination demonstrated a WHO Grade I well-differentiated NET with lymphovascular invasion and negative resection margins. Immunohistochemistry showed positivity for pan-cytokeratin, synaptophysin, chromogranin, INSM1, and CD56. This case highlights the diagnostic challenge of primary mesenteric NETs and supports surgical resection as the definitive management. Careful postoperative surveillance is warranted due to the potential for recurrence.