Extent of smooth muscle resection during mucosectomy and ileal pouch-anal anastomosis affects anorectal physiology and functional outcome

PURPOSE: In patients undergoing colectomy with ileal pouch-anal anastomosis, controversy exists regarding the necessity for and appropriate extent of rectal mucosal resection. Our aim was to assess histologically the extent of anorectal smooth muscle resected at the time of mucosal proctectomy and to correlate this with postoperative bowel and anal sphincter function. METHODS: Surgical specimens of 79 patients undergoing colectomy, mucosal proctectomy, and ileal pouch-anal anastomosis were examined his tologically in a blinded fashion, and the content of smooth muscle in the mucosal proctectomy specimens was scored. Degree of smooth muscle resection was correlated with postoperative anorectal manometry and with functional outcomes, including stool frequency and nocturnal leakage of stool after 3 and 12 months of follow-up. RESULTS: Degree of smooth muscle loss correlated with decreased resting pressure of the internal anal sphincter as early as three months after surgery (r = -0.26; P = 0.03), and the correlation was even stronger after 12 months (r = -0.37; P = 0.005). Decreases in resting pressure were related, in turn, to increased stool frequency at 12 months (r = 0.32; P = 0.02), but stool frequency was also inversely related to volume of the ileal pouch (r = -0.27; P = 0.05). Multivariate analysis confirmed that resting pressure and pouch volume were both significant determinants of stool frequency. The likelihood of nocturnal stool leakage at 12 months was primarily a function of stool frequency (P < 0.01) but also increased with patient age (P < 0.02). CONCLUSIONS: These findings indicate that loss of resting pressure of the internal anal sphincter can be correlated with the extent of smooth muscle resection during rectal mucosectomy and that these factors, in turn, correlate with increased stool frequency and a greater likelihood of nocturnal stool leakage. Consequently, an optimum functional result requires care in identifying and preserving maximum anorectal smooth muscle during mucosectomy.