Int J Colorect Dis (1994) 9:50 Correspondence Nerve regeneration across eoloreetal anastomoses after low anterior resection in a canine model Col6 eetal Disease 9 Springer-Verlag 1994 Dear Sir, We read with interest the article by Horgan et al. investi- gating the mechanisms underlying the recto-anal inhibi- tory reflex [1]. Our group was amongst the first to recog- nise the return of the reflex after restorative proctocolec- tomy with double stapled end-to-end anastomosis [2]. However, there remains controversy over whether the reflex returns after such a procedurein man. A number of questions arise from the above paper. How was the sutured anastomosis performed. If the anastomosis was 5 cm from the anal verge then we pre- sume that the sutures were placed from the outside, with bowel wall inversion. If we believe that nerve regenera- tion can occur across an inverted stapled anastomosis, then there is no reason why the same should not occur across an inverted sutured anastomosis. This would ex- plain the return of the reflex in both group of dogs in this study. An interesting group to study would be those with an endo-anal sutured anastomosis, the proximal bowel being placed within a muscular cuff, denuded of rnucosa, as in restorative proctocolectomy with mucosal proc- tectomy, and as in colo-anal anastomosis as performed in some centres [3]. In such an anastomosis there would be little scope for nerve regeneration across the anastomosis and hence one would not expect the reflex to return, consistent with the authors conclusions. Why did the reflex not return in one of the dogs in which nerve regeneration apparently occurred? The au- thors felt that this was best explained by the possibility that important interneural connections had not been made. However, there was no actual histological differ- ence between this particular anastomosis and the other eight in which nerve regeneration apparently occurred. Of particular note, the reflex was present in one of the dogs at only 10 days after operation? How do the authors explain this? Surely it would be too soon for nerve regen- eration to occur, and suggests another mechanism may be responsible. Yours faithfully, Michael E.R. Williamson (Research Fellow) Wyn G. Lewis (Lecturer in Surgery) The General Infirmary at Leeds Great George Street Leeds LS1 3EX UK References 1. Horgan AF, Molloy RG, Coulter J, Sheehan M, Kirwan WO (1993) Nerve regeneration across colorectal anastomoses after low anterior resection in a canine model. Int J Colorect Dis 8:167 -169 2. Holdsworth PJ, Johnston D (1988) Anal sensation after restora- tive proctocolectomy for ulcerative colitis. Br J Surg 75: 993-996 3. Lane RHS, Parks AG (1977) Function of the anal sphincter following colo-anal anastomosis. Br J Surg 64:596-599 Author's reply Dear Editor, We thank Drs. Williamson and Lewis for their queries regarding the above and we are happy to answer the questions which they raise as follows: The anastomoses were fashioned with interrupted prolene sutures picking up the seromuscular layers and invaginating the mucosa. We agree that it is not surpris- ing that nerve regeneration should take place across such an anastomosis. We are unable to explain why the reflex did not return in one animal. There was no clinical or histological ac- companiment to explain this. It is most inconvenient that a reflex was present at 10 days in 1 animal. Of course nerve regeneration could not have taken place at this time. It is conceivable that bal- loon dilatation above the anastomosis might in some way, stimulate the distal bowel mechanically to cause a reflex. Yours sincerely, Professor w.O. Kirwan, M. Ch., FRCS Cork Regional Hospital Wilton Cork Ireland