Observations upon the aetiology and treatment of complete rectal prolapse.

The classical abnormalities found in patients with complete rectal prolapse--wide deep pelvic peritoneal pouch, unsupported redundant rectum with long mesorectum, weak pelvic floor and anal sphincters--are probably effects rather than causes. "Pelvic floor weakness" must explain few cases, since old age, multiparity, uterine prolapse, are found in a minority. The fact that operations which do no more than fix the rectum in the sacral hollow are most successful and often cure incontinence if present is the best evidence that lack of support of the rectum is a prime cause of prolapse--but it is equally likely that such operations work by preventing intussusception, now regarded as the likely mechanism (rather than sliding herniation) of complete rectal prolapse. It is suggested that rectal prolapse is usually due to straining at defaecation against a closed levator-ani--anal-sphincter mechanism, producing prolapse of the rectum rather than incontinence of faeces. Such straining may be obsessive on the part of patients with psychosocial problems and reduced awareness that the rectum is empty; or it may be due to attempted defaecation with a full rectum in patients with reduced rectal sensation, failure of the afferent arc of the ano-rectal reflex and consequent absence of levator-ani--anal-sphincter relaxation.