[Anorectal functional study. The state of the art].Minerva Chir. 1994 Dec; 49(12):1187-93.MC
Disturbances of anal continence and evacuation are frequent. Numerous techniques are now available to measure anorectal function. There is also a better understanding of the anatomy and physiology of the pelvic floor which has a major role in anorectal function. ANORECTAL MANOMETRY. Manometry of the anal canal is an index of the resistance of sphincters to the passage of faeces. Resting pressure is due mainly to the internal anal sphincter whereas voluntary contraction is due mainly to the external anal sphincter. Anorectal manometry is essential in measuring the length of the anal canal and in establishing the presence of the rectoanal inhibitory reflex. Several techniques are employed to evaluate anorectal manometry which is useful in the investigation of patients with faecal incontinence and constipation. PUDENDAL LATENCIES: Pudendal latencies are valuable in the study of the innervation of the external anal sphincter. Pudendal latencies are measured thanks to the stimulation of the S2-S4 nerves lying in the proximity of the ischial spine through the use of a special glove (St Mark's glove). Prolonged pudendal latencies are typical of neurogenic faecal incontinence but it can be brought about by childbirth, rectal prolapse, obstructed defecation and old age. ELECTROMYOGRAPHY. Electromyography is useful in the study of the function of the pelvic floor. This technique can be performed with single fibre needles which make it possible to measure the action potentials and the fibre density of the muscular fibres. Fibre density is raised in neurogenic faecal incontinence and the action potentials are polyphasic in this condition. Concentric needles are employed to map the anal sphincters and this is useful for evaluating the extent of the damage caused by traumatic events like a third degree tear. ANAL ENDOSONOGRAPHY. Anal ultrasound is very effective in the study of the morphology of the anal sphincters and it requires a rectal probe fitted with a 7-MHz transducer. It is as accurate as electromyography in evaluating the damage to the anal sphincters but it is not painful and it is more acceptable to the patient. DEFECOGRAPHY. This radiological test is a dynamic study of the pelvic floor during defecation. It is very useful for investigating the function and the morphology of the rectum and the pelvic floor during defecation. Important parameters like: the anorectal angle, the opening of the anal canal, the position of the pelvic floor and the descent of the perineum can be evaluated with this test. Defecography is useful in the study of patients with rectal prolapse and constipation.