Sessile serrated lesions of the appendix: a contemporary review of the literature

INTRODUCTION: Sessile serrated lesions (SSLs) of the appendix remain a controversial entity due to evolving definitions, diagnostic criteria, and nomenclature. Shifts in diagnostic thresholds - from multiple serrated crypts to a single unequivocally serrated and distorted crypt - have led to discrepancies in lesion classification and retrospective analyses. These controversies, compounded by inconsistent adherence to updated criteria, highlight the need for studies and reviews applying contemporary standards to accurately assess incidence and clinical significance. METHODS: The review protocol was registered in PROSPERO (CRD420261299191). Systematic searches of PubMed, Web of Science, Scopus and Ovid were performed for studies published between 2007 and 2025. Eligible studies reporting clinicopathological features of appendiceal SSLs were included. RESULTS: The reported prevalence of appendiceal SSLs is low (approximately 1.11-5.22‰), but increases with age and is markedly higher in patients with serrated polyposis syndrome. Most lesions are incidentally detected histologically, are often macroscopically inconspicuous, and show dysplasia in a minority of cases (~ 28%). Compared with colonic SSLs, appendiceal lesions are less common, show female predominance, and more frequently harbour KRAS rather than BRAF mutations, suggesting partially distinct molecular pathways. Although occasional co-occurrence with mucinous neoplasms and adenocarcinoma may suggest possible biological links, current evidence is insufficient to define a consistent progression pathway or establish their true malignant potential. CONCLUSIONS: Overall, the current literature is constrained by small sample sizes, heterogeneous study designs, inconsistent reporting, and substantial publication bias, particularly toward unusual or concurrent neoplastic findings. These limitations preclude definitive conclusions regarding the true prevalence, natural history, and malignant potential of appendiceal SSLs. Further large-scale, systematically characterised, and longitudinally followed cohorts with comprehensive molecular profiling are required to clarify their biological behaviour and clinical significance.