Villous regeneration in ulcerative colitis.

Three cases with extensive villous regeneration were identified in a review of 92 colectomy specimens of ulcerative colitis. Villous regeneration was evident grossly as numerous poorly defined zones of velvety mucosa present primarily in the ascending and transverse colon. These zones were characterized histologically by discrete, well-formed villi lined by epithelium with prominent regenerative changes. Occasionally, the epithelium demonstrated an oncocytic appearance that may be the result of adaptive mitochondrial hyperplasia. Distinguishing villous regeneration from epithelial dysplasia may be difficult because several features, including cytologic atypia, dystrophic goblet cells, and a villous configuration, can be seen in both. However, close attention to the nuclear changes and the type of mucous differentiation will aid in the distinction.