The long term effect of sphincter preserving operations for rectal carcinoma on function of the anal sphincter in man

Anal function was studied in 20 normal subjects and in 20 patients who had undergone sphincter-saving resection of the rectum for carcinoma. In each the anastomosis had been constructed 3-7 cm from the anal verge. Inhibition of the internal sphincter was judged to have taken place when distension of a balloon 10 cm from the anal verge produced an immediate fall of at least 20 per cent in resting anal pressure as measured by a balloon probe: inhibition of the external sphincter in response to the same stimulus was defined as complete cessation of EMG activity. Threshold for sensation was the minimal volume of balloon distension required to elicit a response. Maximum tolerable volume was the largest volume of distension tolerated. Inhibition of the activity of the internal sphincter was found in all controls and in 17 of 20 patients. External sphincter activity was inhibited in 16 of 20 controls and 11 of 19 patients. Threshold for sensation and its quality were similar in both groups. Patients had more frequent bowel actions than the controls which is probably explained by significant reductions in resting and pressure and maximum tolerable volume found in patients. These results suggest that some, at least, of the physiological mechanisms subserving continence remain intact after complete or nearly complete excision of the rectum.