Prevalence and preoperative predictors of occult appendiceal neoplasms following appendectomy for acute appendicitis: a retrospective cohort study of 3,573 patients

Abstract Background Occult appendiceal neoplasms are uncommon but clinically important findings in patients undergoing appendectomy for presumed acute appendicitis. This study aimed to determine their prevalence and evaluate preoperative factors associated with occult appendiceal neoplasia. Methods This retrospective cohort study included consecutive patients who underwent appendectomy for presumed acute appendicitis between January 2020 and December 2025. Mucinous neoplasia, neuroendocrine tumors, adenocarcinoma, and sessile serrated lesions identified on final histopathological examination were classified as occult appendiceal neoplasms. Demographic, laboratory, and radiological variables were evaluated using univariate and multivariable logistic regression analyses. Receiver operating characteristic analysis was used to assess the discriminatory performance of age. Results A total of 3,573 patients were included, of whom 39 had occult appendiceal neoplasms (1.09%): mucinous neoplasia ( n = 18), neuroendocrine tumors ( n = 16), sessile serrated lesions ( n = 3), and adenocarcinoma ( n = 2). Patients with neoplasms were older than those without neoplasms (median 43 vs. 30 years, p < 0.001) and had lower WBC and neutrophil counts (both p < 0.001). Increasing age was independently associated with occult appendiceal neoplasia in the primary multivariable model (adjusted OR 1.05 per year, 95% CI 1.03–1.07; p < 0.001), and the association remained consistent in the exploratory sensitivity model. Age showed moderate discrimination (AUC = 0.705, 95% CI 0.615–0.794). At the exploratory, data-derived 40-year cutoff, sensitivity was 66.7% and specificity was 75.6%. Neoplasm prevalence was 0.48% among patients aged < 40 years and 2.93% among those aged ≥ 40 years, corresponding to an absolute difference of 2.45% points (OR 6.21, 95% CI 3.18–12.14). Plastron appendicitis had the highest observed prevalence (6.38%; 3/47), although this estimate was based on very few events and was exploratory. In a post-hoc exploratory analysis excluding neuroendocrine tumors, the prevalence of non-neuroendocrine appendiceal neoplasms reached 3.10% among patients aged ≥ 50 years. Conclusions Occult appendiceal neoplasms were identified in approximately 1% of appendectomy specimens. Increasing age was independently associated with occult appendiceal neoplasia, with a higher observed prevalence among patients aged ≥ 40 years. Although a higher prevalence was observed among patients with plastron appendicitis, this estimate was based on very few events and should be considered exploratory. These findings support increasing age as a potential factor for preoperative risk stratification, whereas the association between appendicitis severity and occult neoplasia requires confirmation in larger cohorts.