• APPENDIX
• Pathology, Surgical
• Colorectal Neoplasms

Serrated lesions in the gastrointestinal tract (GIT) have attracted much attention in the last decade or so with several publications addressing diagnostic criteria, harmonisation of interobserver variability, terminology, and immunohistochemical and molecular features.1–5 This has culminated in the recognition of distinct lesions that are characterised by stellate or saw-toothed luminal profiles but with unique morphological features that allow for their separation. Molecular elucidation has resulted in the so-called serrated molecular pathway which underpins this family of serrated lesions.6 7 As such, hyperplastic polyps (HP), sessile serrated lesions without dysplasia (SSL) and with dysplasia (SSL-D), traditional serrated adenoma (TSA) and serrated adenocarcinoma are well-recognised diagnoses in the colorectum.

However, in the appendix, which is often regarded as an extension of the right colon, serrated lesions are less well recognised and/or defined compared with their colorectal counterparts. This is due in part to their relative rarity but also that there is coexistent appendicitis which obscures the lesion. Another confounding issue is the concurrence of both serrated and mucinous lesions in the appendix. It is because of this coexistence that serrated appendiceal lesions (SAL) should not be viewed in isolation from primary appendiceal mucinous neoplasms.

While straightforward caricatures of the described entities present no problem, there remains a residua of lesions that are challenging to categorise.

The scope of this viewpoint is to provide useful practical guidelines to the practising pathologist by highlighting commonly encountered diagnostic dilemmas when confronted by serrated and/or mucinous lesions in the appendix.