Case report of an appendiceal neuroendocrine tumor (carcinoid) combined with a parovarian cyst in an adolescent

Background Appendiceal neuroendocrine tumors (NETs) are rare in adolescents and typically an incidental finding, making preoperative diagnosis difficult. We report an exceptional case of an appendiceal NET coexisting with a parovarian cyst in an adolescent, highlighting the diagnostic challenge and management of this rare combination. Case report A 16-year-old female presented with a one-day history of migratory right lower quadrant abdominal pain and fever (38.3 °C). Examination showed right lower quadrant guarding with McBurney’s point tenderness and rebound tenderness. Ultrasound revealed a thickened appendix (max diameter 1.23 cm) and a right adnexal anechoic cyst (3.92 × 2.70 × 2.09 cm). Transumbilical single-port laparoscopy demonstrated a congested, edematous appendix with a firm 1.3-cm diameter area 3–4 cm from its base, and a well-defined 4.0 × 3.0 × 2.0 cm cystic mass within the right broad ligament. Appendectomy and parovarian cyst enucleation were performed. Pathology confirmed a well-differentiated neuroendocrine tumor (G1,WHO classification) in the appendiceal muscularis, with positive immunohistochemistry for CD-56, chromogranin A (Cg-A), cytokeratin low molecular weight (CK-LMW),Syn and Ki-67. The parovarian lesion was a serous cystadenoma. The patient recovered well with no recurrence over 7 years of follow-up. Conclusion Appendiceal NETs are rare in adolescents, often presenting as acute appendicitis, and are difficult to diagnose preoperatively. Its combination with a parovarian cyst is even rarer. Transumbilical single-port laparoscopic surgery enabled simultaneous diagnosis and treatment in this case.