Misplaced epithelium in ulcerative colitis and Crohn's disease of the colon and its relationship to malignant mucosal changes.

The presence of misplaced mucosal epithelium was studied in the colectomy specimens from 30 patients with Crohn's disease, 30 patients with ulcerative colitis, 15 patients with ulcerative colitis complicated by carcinoma and 30 patients with non-colitic colorectal carcinoma. Misplaced epithelium was present in 21 (70%) of the resection specimens with Crohn's disease, 20 (66.7%) with ulcerative colitis and 12 (80%) with ulcerative colitis complicated by carcinoma. None of the specimens with non-colitic colorectal adenocarcinoma showed misplaced foci of epithelium. Two pathogenetic mechanisms for epithelial misplacement are proposed: (1) the effects of mucosal inflammation and repair; and (2) muscular abnormalities in inflammatory bowel disease. The proposed mechanisms and patterns of epithelial misplacement are discussed and illustrated. The importance of its recognition is emphasized because, when associated with mucosal dysplasia, difficulties in interpretation arise in distinguishing it from 'early' invasive adenocarcinoma. Epithelial misplacement is common in patients with longstanding ulcerative colitis and may be a factor in increasing the significance of pre-existing mucosal dysplasia and promoting the development of adenocarcinoma. This may explain the unusual growth pattern encountered in ulcerative colitis, of submucosal cancer underlying a flat, non-dysplastic mucosa.