[Pathomorphology of ulcerative colitis]

Microscopic and macroscopic appearances of ulcerative colitis (UC) by its phase of inflammation were summarized. The most characteristic microscopic findings of active phase UC is diffuse lymphoplasmacytic infiltration, essentially associated with basal plasmacytosis. Although inflammation of UC is basically limited to the mucosa, active inflammation extends into the submucosa in some instance, and acute ischemic change is overlapped to cause toxic megacolon. In remission phase, inflammation is reduced and goblet cell mucus is fully recovered but evidences of the past inflammation such as irregular shape and disarrangement of crypts, Paneth cell metaplasia, thickening of the muscularis mucosae and discrepancy between the crypt base and the muscularis mucosae are usually demonstrated. Macroscopic appearances of UC reflect its microscopic findings such as degree of inflammation, whether inflammation is (was) limited to the mucosa or extend(ed) into the submucosa. Active phase is classified into erythematous, spongy, granular, pseudopolyp, ulcerative, and fulminant (toxic megacolon) type. In the former two types, inflammation is limited in the mucosa, and the latter two types are associated with ischemic change. In remission phase, erythematous and spongy types recover to the almost normal looking mucosa or fine granular mucosa with preservation of mucosal folds, granular type recovers to granular, fine granular or flat atrophic mucosa without preservation of mucosal folds, and pseudopolyp type recovers to mucosa with inflammatory polyposis.