Oncologic Risk of Missed Appendiceal Tumors in Acute Appendicitis

Importance: Antibiotic-only management (AOM) for uncomplicated acute appendicitis is increasingly adopted, raising concern about missed appendiceal neoplasms. Objective: To assess the prevalence, histologic spectrum, and predictors of incidental appendiceal tumors after appendectomy for acute appendicitis. Design, Setting, and Participants: This single-center retrospective cohort study was conducted from January 1, 2013, to December 31, 2021, at the tertiary surgical emergency center at Saint-Antoine Hospital in Paris, France. All consecutive adult patients undergoing appendectomy for acute appendicitis were eligible for inclusion. Data were analyzed in June 2025. Exposure: Standard surgical management with appendectomy (no AOM); preoperative clinical variables, laboratory values, and imaging findings were assessed as potential predictors of appendiceal tumors. Main Outcome and Measures: Prevalence and histopathological classification of incidental appendiceal neoplasms identified after appendectomy for acute appendicitis and preoperative clinical and radiologic factors associated with aggressive tumors. Results: Among the cohort, median (IQR) age was 32 years (25-43), and 999 patients (44%) were female. Among 2293 appendectomies, 37 (1.6%) had malignant or premalignant lesions and 8 (0.3%) had benign nondysplastic lesions. Neuroendocrine tumors (NETs) (n = 22) predominated; all were grade 1 (G1) and smaller than 2 cm, with 19 (86%) measuring 1 cm or less without recurrence after 34 months of follow-up. Other lesions included low-grade appendiceal mucinous neoplasms (n = 5), metastatic tumors (n = 3), goblet cell carcinomas (n = 2), mucinous adenocarcinoma (n = 1), and low-grade dysplastic polyps (n = 4). Compared with nonneoplastic appendicitis, aggressive tumors (putting aside G1 NETs <2 cm and low-grade dysplasia) occurred more often in older patients (median [IQR] age, no malignant lesions: 32 years [25.0-43.0] vs malignant lesions: 45.0 years [37.8-57.2]; P = .03), with longer median symptom duration (no malignant lesions: 2 days vs malignant lesions: 1 day; P < .001), larger median (IQR) appendiceal diameter (no malignant lesions: 11.0 mm [9.0-13.0] vs malignant lesions: 18.0 mm [14.0-25.5]; P < .001), and radiologic suspicion of complicated appendicitis (no malignant lesions: 287 of 2234 [13%] vs malignant lesions: 6 of 11 [55%]; P = .001). In dedicated univariate analysis, NETs could not be distinguished from nonneoplastic appendicitis by any clinical or radiological variables tested. Using eligibility criteria for AOM derived from the univariate analysis (abdominal pain duration <14 days; age <60 years; and on imaging: uncomplicated appendicitis, appendiceal diameter <15 mm, and absence of suspicious appendiceal, peritoneal, hepatic, or bone lesions), none of the patients with aggressive tumors met the entirety of these criteria. However, 17 of 22 small G1 NETs (77%) and 1 of 4 low-grade dysplastic polyps (25%) fulfilled these criteria. By grouping all these selection criteria, 74% of the cohort met eligibility criteria for potential AOM; within the subgroup with uncomplicated appendicitis, 85% would have been eligible. Conclusions and Relevance: In this single-center cohort study, incidental appendiceal tumors were mostly small and low-grade NETs; aggressive malignancies were exceptional and occurred in identifiable high-risk profiles. Applied assembled preoperative selection criteria reliably excluded patients with aggressive tumors, thereby supporting the oncologic safety of AOM in rigorously selected individuals.