Why do some patients experience poor functional results after anterior resection of the rectum for carcinoma?

The aim of this study was to examine the dynamic inter-relationship of the anal sphincter, residual rectum, and neorectum after low anterior resection for rectal carcinoma.

Seventy-three patients underwent laboratory tests of anorectal function a median of ten (range 1-100) months after operation. All patients completed quality of life questionnaires and had the level of their anastomoses determined by rigid sigmoidoscopy. Forty-four patients (60 percent) had some form of disturbance of bowel function, which was classified as "poor" function if bowel frequency was four or more in 24 hours and if there was also either fecal leakage or urgency of defecation. Manometric data were analyzed using stepwise logistic regression analysis.

Only two factors were found to be significantly and independently associated with poor bowel function, namely, the pressure recorded in the upper part of the anal sphincter in response to distention of the neorectum (15 (7-24) cm of water in patients with poor function vs. 29 (15-58) cm in patients with good function; P < 0.005) and the level of the anastomosis above the anal sphincteric high pressure zone (2.5 (2-3.5) cm in patients with poor function vs. 6 (4-12) cm in patients with good function; P < 0.005).

Continence after anterior resection is related to an appropriate "sampling" response in the anal sphincter to activity within the neorectum. This in turn, is directly related to length of the residual rectum, which is, therefore, of crucial importance to function.