Incomplete Mucosal Layer Excision during Endoscopic Mucosal Resection: a potential source of recurrent adenoma

BACKGROUND AND AIMS:Residual or recurrent adenoma detected during surveillance (RRA) is the major limitation of endoscopic mucosal resection (EMR). The pathogenesis of RRA is unknown although thermal ablation of the post-EMR defect (PED) margin reduces RRA. We aimed to identify a feature within the PED which could be associated with RRA. METHODS:Between 1/2017 and 7/2020 detailed prospective procedural data on all EMR procedures performed at a single centre were retrospectively analysed. At the completion of EMR the PED was systematically examined for features of incomplete mucosal layer excision (IME). This was defined as a demarcated area within the PED bordered by a white electrocautery ring, containing endoscopically identifiable features suggesting incomplete resection of the mucosa including lacy capillaries and/or visible fibres of the muscularis mucosae. Areas of IME were re-injected and re-excised by snare and submitted separately for blinded specialist gastrointestinal pathologist review. RESULTS:EMR was performed for 508 large non-pedunculated colorectal polyps (LNPCPs) (median size 35mm). In 10 PED (2.0%) an area of IME was identified and excised. Histopathological examination of areas of suspected IME demonstrated muscularis mucosae in 9/10 (90%), residual lamina propria in 9/10 (90.0%) and residual adenoma in 5/10 (50.0%). No RRA was detected during follow-up after re-excision of IME. CONCLUSION:We report the novel finding of IME within the PED after EMR of LNPCPs. IME may contain microscopic residual adenoma and therefore is a risk for RRA during follow-up. After completion of EMR the PED should be carefully evaluated and if IME is found it should be excised.