Mechanical Small Bowel Obstruction Secondary to Low-Grade Appendiceal Mucinous Neoplasm: A Case Report.

Low-grade appendiceal mucinous neoplasm (LAMN) is an uncommon epithelial tumor that is frequently diagnosed incidentally and only rarely produces mechanical small bowel obstruction, with previous reports limited to isolated cases. We describe a 53-year-old man with a four-day history of periumbilical pain, obstipation, nausea, and bilious vomiting. Examination showed abdominal distension, decreased bowel sounds, and rebound tenderness. Contrast-enhanced computed tomography (CT) demonstrated a 7 cm heterogeneous right hemiabdominal mass with pericecal fat stranding that favored, but did not definitively establish, an appendiceal origin, prompting emergency exploratory laparotomy. Intraoperatively, a markedly dilated, mucin-filled appendix was densely adherent to the terminal ileum, producing mechanical small bowel obstruction; careful adhesiolysis and en bloc appendectomy were performed without rupture of the lesion. Histopathology confirmed LAMN with negative circumferential and basal margins and no lymphovascular, perineural, or lamina propria invasion, staged as pTis(LAMN) per the American Joint Committee on Cancer (AJCC) eighth edition. The postoperative course was uneventful, with oral intake resumed at 48 hours and discharge on postoperative day 3. Surveillance included clinical review at two weeks and three months, with double-contrast CT planned at six months and joint follow-up with oncologic surgery. This case highlights dense adhesion to the terminal ileum, rather than perforation, torsion, or internal herniation, as a rare mechanism of LAMN-related obstruction, and reinforces that atraumatic surgical handling is essential to avoid mucin spillage and pseudomyxoma peritonei.