A Grade 1, Metastatic, Well-Differentiated Neuroendocrine Tumor Presenting as Closed-Loop Small Bowel Obstruction With Ischemic Bowel.

Small bowel neuroendocrine tumors (NETs) are typically indolent neoplasms that often present with vague abdominal symptoms and are frequently diagnosed only after regional or metastatic spread has occurred. Mesenteric nodal metastases may provoke a desmoplastic reaction resulting in bowel tethering, luminal narrowing, mesenteric vascular compromise, obstruction, and intestinal ischemia. We report the case of a 49-year-old man with no prior abdominal surgery who presented with three months of intermittent abdominal pain followed by abrupt worsening to diffuse severe abdominal pain and emesis. Computed tomography demonstrated small bowel obstruction with concern for a closed-loop obstruction at the level of a 2.5 × 1.6 cm mesenteric mass, with associated bowel wall thickening concerning for ischemia. The patient underwent emergency exploratory laparotomy with resection of strangulated small bowel, en bloc resection of a stellate mesenteric mass, primary anastomosis, and appendectomy. Pathology demonstrated mesenteric lymph nodes positive for metastatic well-differentiated NET, grade 1, with extranodal extension and lymphatic space invasion. Tumor cells were positive for synaptophysin, chromogranin, CD56, and CK AE1/AE3, with a Ki-67 index of less than 1%. No definite primary lesion was identified in the resected bowel specimen, but the overall clinicopathologic findings strongly suggested an occult small bowel primary. The postoperative course was uncomplicated, and the patient improved clinically after surgery. This case highlights that even low-grade NETs may first present as a surgical emergency due to mesenteric metastatic disease and fibrosis rather than carcinoid syndrome. In patients with a virgin abdomen, chronic intermittent abdominal pain, weight loss, and an obstructing mesenteric mass, small bowel NET should remain in the differential diagnosis.