Characterization of endoscopic features and histology of a distinct mucosal transition zone on the ileocecal valve (with video)

Background and Aims: We have endoscopically encountered a zone of transitional mucosa between the colonic and ileal mucosa located in a 3- to 10-mm-wide ring around the ileocecal valve (ICV) orifice. We aimed to describe the features of the ICV transitional zone mucosa. Methods: We used videos and photographs from normal ICVs and biopsy samples from normal colonic mucosa, transitional zone mucosa, and normal ileal mucosa to characterize the endoscopic and histologic features of the ICV transitional zone mucosa. Results: The ICV transitional zone is identifiable on every ICV without a circumferential adenoma or inflammation that obliterates the zone. The zone is characterized endoscopically by an absence of villi, which distinguishes it from the ileal mucosa, but the pits are more tubular and with more prominent blood vessels compared with normal colonic mucosa. Histologically, the villi of the transitional zone are blunted, and the amount of lymphoid tissue is intermediate between the colonic mucosa and ileal mucosa. Conclusions: This is the first description of the normal transitional zone of mucosa on the ICV. This zone has unique endoscopic features that should be recognized by colonoscopists and that can potentially create difficulty in identifying the margins of adenomas located on the ICV.