LONG-TERM HISTOMORPHOLOGICAL SURVEILLANCE OF THE PELVIC ILEAL POUCH - DYSPLASIA DEVELOPS IN A SUBGROUP OF PATIENTS

Background & Aims: Little is known about the longterm morphology of the pelvic ileal pouch after restorative proctocolectomy in patients with ulcerative colitis. This study analyzed the mucosal adaptation in the pouch during a long-term follow-up. Methods: Mucosal biopsy specimens were obtained from 87 patients during a follow-up of 6.3 years (SD, 2.7; range, 3-14 years). The villous surface density, degree of inflammation, and type of mucin were determined from glycolmethacrylate-embedded sections. Results: Three basic patterns of mucosal adaptation were observed: regular response with normal mucosa or mild villous atrophy and no or mild inflammation (type A, 51%), transient atrophy response with temporary moderate or severe villous atrophy followed by normalization of architecture (type B, 40%), and constant atrophy response with permanent subtotal or total villous atrophy developing from the early functioning period accompanied by severe pouchitis (type C, 9%). Low-grade dysplasia occurred in 3 patients with type C response. Conclusions: In a small group of patients with ulcerative colitis, the mucosa of the pelvic pouch adapts with constant severe villous atrophy accompanied by long-standing pouchitis. This group of patients should be identified and undergo regular endoscopic and histomorphological surveillance because of risk of developing neoplasia in the pouch mucosa.