Incidence and natural history of dysplasia of the anal transitional zone after ileal pouch-anal anastomosis

PURPOSE: Preservation of the anal transitional zone during ileal pouch-anal anastomosis is still controversial because of the risk of dysplasia and the theoretical risk of associated cancer. Without long-term follow-up data, the natural history and optimal treatment of anal transitional zone dysplasia are unknown. The aim of this study was to determine the long-term risk of dysplasia in the anal transitional zone and to evaluate the outcome of a conservative management policy for anal transitional zone dysplasia. METHODS: Two hundred ten patients undergoing anal transitional zone-sparing ileal pouch-anal anastomosis for ulcerative or indeterminate colitis between 1987 and 1992 and who were studied with serial anal transitional zone biopsies for at least five years postoperatively were included. Median follow up was 77 (range, 60–124) months. RESULTS: Anal transitional zone dysplasia developed in seven patients 4 to 51 (median, 11) months postoperatively. There was no association with gender, age, preoperative disease duration or extent of colitis, but the risk of anal transitional zone dysplasia was significantly increased in patients with prior cancer or dysplasia in the colon or rectum. Dysplasia was high grade in one and low grade in six. Two patients each with low-grade dysplasia detected on three separate occasions underwent mucosectomy 29 and 38 months after detection of low-grade dysplasia, but no cancer was found. The five other patients with dysplasia on one or two occasions were treated expectantly and were apparently dysplasia-free for a median of 72 (range, 48–100) months. CONCLUSIONS: Anal transitional zone dysplasia after ileal pouch-anal anastomosis is infrequent, is most common in the first two to three years postoperatively and may apparently disappear on repeated biopsy. Anal transitional zone preservation did not lead to the development of cancer in the anal transitional zone after five to ten years of follow-up. Long-term surveillance is recommended to monitor dysplasia. If repeat biopsy confirms persistent dysplasia, anal transitional zone excision with neoileal pouch-anal anastomosis is recommended.Presented at the meeting of The American Society of Colon and Rectal Surgeons, San Antonio, Texas, May 2 to 7, 1998.