Triple synchronous appendiceal neoplasms with pseudomyxoma peritonei—a case report of a rare and unfortunate entity and literature review

Background: Appendiceal neoplasms are rare tumours, with synchronous tumours in the same appendix being only sparsely reported in the literature. Appendiceal mucinous neoplasms account for nearly one-third of all appendiceal epithelial tumours and can be classified as low-grade appendiceal mucinous neoplasms (LAMN), high-grade appendiceal mucinous neoplasms (HAMN) and appendiceal mucinous adenocarcinoma. Each of these neoplasms has different implications on patient outcomes and therefore requires careful consideration when planning treatment options. Pseudomyxoma peritonei (PMP) is a rare condition that can be seen especially in association with appendiceal mucinous neoplasms and can cause significant morbidity and mortality. We report a unique case of synchronous LAMN, HAMN, and appendiceal adenocarcinoma within the same appendix, complicated by PMP.

Case Description: A 49-year-old woman with no significant medical history presented with severe abdominal pain and a 2-year history of progressive abdominal distention. A computed tomography (CT) scan revealed massive intra-abdominal mucinous ascites and hollow viscus perforation. Following initial emergency laparotomy and washout, she was discussed at the multidisciplinary meeting and deemed a candidate for definitive surgical intervention. Right hemicolectomy was performed given the presence of invasive adenocarcinoma and caecal involvement, while cytoreductive surgery and hyperthermic intraperitoneal chemotherapy were performed to address the extensive peritoneal disease consistent with PMP. Complete cytoreduction was achieved (CC0). Histopathological evaluation of the resected specimen revealed three synchronous tumour types within the same appendix: LAMN, HAMN, and adenocarcinoma, staged at pT4a pN0 pM1c with low-grade PMP. This patient has no signs of recurrence after 2 years of surveillance.

Conclusions: Despite the histopathological complexity of triple synchronous appendiceal neoplasms complicated by PMP, complete cytoreduction was achievable and associated with favourable short-term outcomes, with no evidence of recurrence at 2 years of surveillance. Prognosis in such cases appears to be guided primarily by the grade of peritoneal disease rather than the appendiceal primary, supporting an encouraging outlook for patients with low-grade PMP regardless of the histological complexity of the primary tumour. A multidisciplinary approach and thorough histopathological assessment are essential to ensure appropriate staging, prognostication and individualised treatment planning in this rare and complex entity.