Pattern of mucosal adaptation in acute and chronic pouchitis

Variant pathological changes have been observed in ileoanal pouches, including inflammation, villous atrophy, and crypt hyperplasia. Therefore, we investigated the type and degree of mucosal adaptation in patients with ulcerative colitis and familial adenomatous polyposis. Forty-two patients with ulcerative colitis and 14 patients with familial adenomatous polyposis with ileoanal pouches were assessed. Samples were taken from three months to eight years after creation of an ileoanal pouch. Mucosal architecture was examined by morphometry after microdissection. Structural changes of the mucosa can be categorized into three groups. Compared with preoperative values, patients without pouchitis (73 percent) has only minor decrease of villous length (402 microm vs. 540 microm) and increase in crypt depth (274.5 microm vs. 177 microm). In patients with acute pouchitis (20 percent), a slight increase in villous length (477 microm vs. 402 microm) and pronounced crypt hyperplasia (376 microm vs. 274.5 microm) was observed compared with noninflamed ileoanal pouches. In contrast, in patients with chronic pouchitis (7 percent), severe villous atrophy (62.5 microm) and crypt hyperplasia (543 microm) was found. Minor structural changes of ileoanal pouch mucosa develop early as an adaptive response to a new environment. Only in a small group of patients with chronic pouchitis does severe villous atrophy and crypt hyperplasia of the ileoanal pouch mucosa develop, most likely as a consequence of mucosal inflammation.