Serial evaluation of anorectal function following low anterior resection of the rectum

This prospective study was performed to serially assess the changes in anorectal function after low anterior resection of the rectum, and to elucidate the mechanisms of functional impairment and the recovery process.

Thirty-two patients undergoing low anterior resection for rectal cancer were evaluated prospectively. Standardized interviews concerning anorectal function and physiologic studies consisting of manometry and balloon proctometry were performed preoperatively, then at 1, 3, and 6 months, and 1 year after the operation. Depending on the length of the residual rectum, patients were divided into two groups: (1) shorter than 4 cm (the short group, n = 18), and (2) longer than or equal to 4 cm (the long group, n = 14).

Postoperatively, stool frequency increased and urgency to defecate occurred, which continued until 3-6 months had passed and was more remarkable in the short group. Overall incontinence score increased, which was more remarkable in the short group. Anal resting pressure showed a moderate reduction after 3 months, whereas squeeze pressure did not decrease significantly. Rectoanal inhibitory reflex was postoperatively abolished in almost all patients in the short group, which showed nearly no recovery for 1 year. In the long group, it persisted postoperatively in half the cases, and the reflex returned in a few cases within 1 year. Balloon proctometry revealed overall reduction in rectal capacity and compliance. Although the values tended to recover steadily, they did not reach the preoperative level for 1 year. Urgent volume and maximal tolerable volume remarkably declined, which continued for 1 year and for 6 months, respectively. Rectal compliance also decreased considerably, which continued for 6 months. Most values of rectal capacity tended to be smaller in the short group.

Impairment of continence after low anterior resection seemed multifactorial, including diminished rectal capacity and compliance, impaired internal anal sphincter tone, and loss of rectoanal inhibitory reflex. Clinical outcome was better and reduction in rectal capacity was less in patients whose rectum remained more than 4 cm. Most of the functional impairments clinically recovered by 6 months postoperation. In the process of clinical recovery of continence, restoration of rectal capacity and compliance and internal anal sphincter tone seemed to contribute a significant degree, while the rectoanal inhibitory reflex did not contribute as much.