Purpose: This study was undertaken to investigate the morphologic and functional changes with time in the mucosa of the ileoanal pouch.
Methods: A morphologic study by histopathologic analysis, mucosal morphometry, and mucin histochemistry and a functional study by analysis of transmucosal potential difference were performed in 27 patients with an ileoanal J-pouch after restorative proctocolectomy for ulcerative colitis. In 19 patients with a normal ileoanal pouch, two prospective follow-up analyses were performed after median functional pouch times of 14 and 39 months. We also evaluated eight patients with the diagnosis of pouchitis (median follow-up, 52.5 months).
Results: In the normal ileoanal pouch group, some degree of chronic and acute inflammatory infiltration was identified in 100 percent and 63.2 percent of cases, respectively, with no significant differences being observed between the two follow-up analyses. The mean villous atrophy index at the first and second follow-up was 0.54 and 0.52, respectively, significantly lower (P < 0.001; an indication of a greater degree of villous atrophy) than the value obtained from the control group with a healthy terminal ileum (0.77). The group of patients with pouchitis exhibited statistically significant differences in the degree of acute and chronic inflammatory infiltration, the extent of ulceration, the crypt depth, and the villous atrophy index, compared with patients without pouchitis. In the normal ileoanal pouch group, the median percentage of sulfomucin with each degree of atrophy (1=mild; 2=moderate; and 3=severe) was 2.6, 4.5, and 20.9 percent, respectively. In patients with pouchitis, the median percentage of sulfomucin was 5.9 percent. The mean transmucosal potential difference at the first follow-up (-25.3 mV) was significantly lower (P=0.001) than at the second (-30.4 mV). Significant differences were apparent with respect to both the normal ileum (-8.9 mV) and the normal rectum (-40.2 mV).
Conclusion: These results suggest that the ileal pouch behaves as a neorectum, with different degrees of colonic metaplasia from a morphologic and a functional perspective.