Purpose: The aim of this study was to examine the serial changes that take place in the first year after low anterior resection for rectal carcinoma, in terms both of anorectal physiology and clinical bowel function. Our hypothesis was that some patients never regain satisfactory anorectal function, because the operative procedure leads to permanent impairment of anorectal reflex and motor function.
Method: Nineteen patients underwent serial tests of anorectal function, before and for one year after low anterior resection. The median level of the anastomosis above the anal high-pressure zone was 3 (range, 1-6) cm.
Results: Anal resting pressure (median (interquartile range)) was significantly decreased three months after operation (62 (46-72) cm H2O) and one year after operation was still significantly less (58 (48-73) cm H2O) than before operation (77 (58-93) cm H2O) (P < 0.01). Maximum tolerated volume in the neorectum decreased from 130 (88-193) ml before operation to 80 (51-89) ml three months after operation (P < 0.005) but returned to preoperative values by six months (125 (60-140) ml) (P = not significant) and remained at these values one year after operation. The volume in the "neorectal" balloon required to elicit a maximum rectoanal inhibitory reflex was significantly less three months after operation than before operation (50 (43-60) ml compared with 100 (73-100) ml; P < 0.005); one year after operation, the volume required was still significantly less than before operation (50 ml vs. 100 ml) (P < 0.015). Bowel frequency increased from 1 (1-2) in 24 hours before operation to 4 (2-5) times in 24 hours after operation and remained at 4 times in 24 hours throughout the first year after operation. Three months after operation, 53 percent of patients experienced some degree of fecal leakage and 24 percent experienced urgency of defecation. These aspects of bowel function improved with time, but even one year after operation, 29 percent of patients continued to experience fecal leakage and 18 percent wore a protective pad.
Conclusions: Anal resting pressure decreased significantly after low anterior resection and did not recover in the course of the first year after operation. Moreover, the volume of an air-filled balloon in the neorectum that was required to elicit maximum inhibition of the anal sphincter was significantly less after anterior resection that before operation. These long-term and presumably permanent changes in physiologic behavior of the anoneorectum after low anterior resection provide an explanation for the failure of some patients to regain satisfactory bowel function following that procedure.