Factors associated with the development of pseudomyxoma peritonei in incidental low-grade appendiceal mucinous neoplasms

Low-grade appendiceal mucinous neoplasm (LAMN) is one of the lesions most frequently encountered incidentally after appendectomy for acute appendicitis, and the commonest primary tumour underlying pseudomyxoma peritonei (PMP). The need for additional treatment and the optimal surveillance of patients with an incidental LAMN remain controversial. We aimed to determine the rate of, interval to, and factors associated with progression to PMP. Patients over 18 years who underwent appendectomy with a preoperative diagnosis of acute appendicitis between 2018 and 2024, and in whom histopathological examination revealed LAMN, were reviewed retrospectively. Demographic, operative, pathological and follow-up data were recorded. Among 1926 appendectomies, 13 patients (0.7%) were diagnosed with LAMN. The median age was 63 years (range 29–78) and 6 patients (46%) were female. The median tumour diameter was 30 mm (IQR 15–35). Completion right hemicolectomy in 2 patients (15%) revealed neither residual tumour nor nodal metastasis. After a median follow-up of 41 months, PMP developed in 3 patients (23%) at 19, 28 and 35 months. Perforation ( p = 0.038), extra-appendiceal mucin ( p = 0.014) and pT4 stage ( p = 0.014) were more frequent in patients who progressed. All three underwent complete cytoreductive surgery with hyperthermic intraperitoneal chemotherapy for low-volume disease (peritoneal cancer index scores 5, 7 and 8) and remain recurrence free. PMP developed in 23% of patients with an incidental LAMN. All patients who progressed had pT4 disease with extra-appendiceal mucin, and most had perforation. Larger, multicentre series are needed to define the optimal follow-up and treatment of these patients.