Preservation of the colo-anal reflex in colonic transection and post-operative Hirschsprung's disease: Potential extrinsic neural pathway.

BACKGROUND: The colo-anal reflex is a distinct reflex whereby the internal anal sphincter (IAS) relaxes in association with colonic high amplitude propagating contractions (HAPCs) in contrast to the recto-anal inhibitory reflex (RAIR), which is characterized by IAS relaxation upon rectal distension. The RAIR is mediated by the myenteric plexus and therefore absent in Hirschsprung disease. We retrospectively assessed the presence and the characteristics of the colo-anal reflex in children in whom large bowel continuity had been surgically disrupted to assess the role of the extrinsic nervous system in the reflex.

METHODS: High-resolution (HR) colonic manometry and HR-anorectal manometry were used to evaluate both colonic and anal motor activity in ten children with treatment-unresponsive slow transit constipation (STC), who had previously undergone left-sided colostomy formation with consequent disruption of the bowel continuity, and in two children with Hirschsprung's disease (HSCR), who had previously undergone distal colon resection followed by Duhamel pull-through. Eight children with STC, normal colonic motor activity, and preserved large bowel continuity served as a control group. The presence and characteristics of colo-anal reflex were analyzed.

KEY RESULTS: In the study group, all patients showed the presence of both normal HAPCs and the presence of the colo-anal reflex. In two cases of HSCR, RAIR was absent; however, both patients demonstrated a colo-anal reflex.

CONCLUSIONS: In children with disrupted continuity of the colon and/or abnormal anal reflex, the colo-anal reflex is still preserved suggesting that it is mediated by a different pathway from the RAIR, possibly an extrinsic neural pathway.