When Lightning Strikes Twice: Synchronous Appendiceal Neoplasms

Document Type

Conference Proceeding

Publication Date

5-2026

Abstract

Appendiceal neoplasms are often clinically silent until later stages, when they may mimic appendicitis with right lower quadrant (RLQ) or nonspecific abdominal pain. Neuroendocrine tumors, while rare in the overall population, are the most common appendiceal malignancies, with a prevalence of approximately 7 per 100,000. In comparison, low-grade appendiceal mucinous neoplasms (LAMNs) make up 0.2–0.3% of appendectomy specimens. Mucoceles, frequently associated with mucinous neoplasms, vary in size, with the largest reported measuring 17 cm by 4 cm in 2005. We report a rare case of a large appendicular mucocele, measuring 10.7 cm by 7.0 cm, with final pathologies of both a LAMN and a neuroendocrine tumor. A 55-year-old male presented to the ED with three days of nondescript RLQ abdominal pain concerning for appendicitis. His history was notable benign polyps on his colonoscopy one year prior. Laboratory studies revealed a WBC 9.1, and CEA 12.5. CT Abdomen/ Pelvis demonstrated a large cystic structure in the RLQ measuring 15 x 10 cm, concerning for a dilated appendix secondary to appendiceal mucocele. The patient was admitted and taken to the OR. Upon entering the abdomen, a large, smooth mass was encountered in the RLQ. After the soft tissue attachments encapsulating and anchoring the mass to the pelvis were bluntly dissected, a right hemicolectomy with ileotransverse anastomosis was performed. Pathology demonstrated a well-differentiated neuroendocrine tumor (carcinoid tumor) of the appendix tip measuring 1.6 cm with vascular invasion and negative surgical margins. Additionally, a LAMN measuring 10.7 cm involving the remainder of the appendix was noted with negative margins. Postoperatively, the patient did well and continues surveillance with medical oncology with yearly CT scans. Mucinous neoplasms are clinically significant due to both their malignant potential and risk of rupture, which may lead to pseudomyxoma peritonei or peritoneal mucinosis. Primary appendiceal tumors are rare, comprising approximately 0.5% of all GIT malignancies. Of these, neuroendocrine tumors are the most common, with a yearly incidence of 0.9 per 100,000 person-years. In comparison, LAMNs have a yearly incidence rate of 0.11 per 100,000 person-years, and in recent case reports, approximately 54% of mucoceles were associated with LAMN. Overall, this is a very interesting case due to the size of the LAMN, a benign colonoscopy 1 year prior, and the presence of two distinct neoplasms. This case highlights the importance of considering appendiceal neoplasms as a differential diagnosis when there is concern for acute appendicitis.(Figure Presented)

Comments

This article was published in Surgical Endoscopy, Volume 40, Issue 2 Supplement.

The published version is available at https://dx.doi.org/10.1007/s00464-026-12851-0.

Copyright © 2026.

Publication Title

Surgical Endoscopy

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