Nerve regeneration across colorectal anastomoses after low anterior resection in a canine model

The disappearance and subsequent return of the recto-anal inhibitory reflex following low anterior resection was investigated using manometric and histological studies. Ten female greyhound dogs were randomised into 2 groups. All underwent low anterior resection. Five had stapled EEA anastomosis of the rectum and 5 were handsewn. The recto-anal inhibitory reflex was measured before and after surgery using a microtransducer tipped catheter. Six months postoperatively the recto-anal inhibitory response was again measured and the animals sacrificed. The colorectal anastomoses were examined histologically using light microscopy to determine the pattern of innervation at the anastomotic site. Manometric studies showed the recto-anal inhibitory reflex present in all cases pre-operatively, in only 1 case on the tenth postoperative day and was present in eight cases after 6 months. Histological examination of longitudinal sections across the anastomoses showed clear evidence of regenerating nerve trunks at the anastomotic site in both stapled and handsewn groups. We conclude that the return of the recto-anal inhibitory reflex is associated with regeneration of intramural autonomic nerves across the anastomotic scar.