Ano-rectal Anomalies: Physiological Considerations.

We have used a classification of ano-rectal anomalies following the concepts of Keith (1908), Stephens (1953a, b), Browne (1955) and Bill and Johnson (1958), as described elsewhere (Nixon, 1961). The low anomalies in which the 'anus' or 'fistula' is below the puborectalis present few serious problems. The main groups are the covered and ectopic anus, and continence is achieved by adequately enlarging the opening where it lies by cutback and dilatation. Transplantation need only be considered later as a secondary procedure in the minority who need it for mainly aesthetic reasons. Puborectalis is intact around the bowel but the external sphincter is behind the anus in the common vulval and vestibular ectopic ani. The rectal sensation is not interfered with by the minor procedures used, but anal sensation must be deficient in these ectopics because the proctodaeum is itself deficient. Apparently it is not necessary under these conditions because the continence is good as shown by Partridge and Gough (1961) in their follow-up of the Great Ormond Street series. In Swenson's procedure for Hirschsprung's disease it seems that the maintenance of anal sensation and the full sphincter complement usually allows continence in the absence of rectal sensation. (In Hirschsprung's disease the internal sphincter does not relax normally; but the same procedure has been used for severe megarectum without aganglionosis, and continence was still maintained.) Thus it seems that there are two sensory and two motor elements normally involved in continence, but loss of one at least may not cause incontinence: rectal sensation (visceral); puborectalis (striated); anal sensation (somatic); external sphincter (striated); internal sphincter (unstriated). The internal sphincter seems to be more concerned with prevention of soiling than frank incontinence. In the 'high' ano-rectal anomalies the bowel stops above the puborectalis sling, and ano-rectal agenesis