What is Anorectal Manometry?
Anorectal manometry is a test performed to evaluate patients with constipation and/or fecal incontinence. Anorectal manometry measures pressures of the anal sphincter muscles and the sensation in the rectum.
What is the Anal Sphincter Mechanism?
The anal sphincter mechanism consists of paired, cylindrical-shaped muscles that surround the anal canal. The sphincter muscle consists of an internal an external component. The external component is larger. This is the muscle you are able to control to maintain continence. The inner muscle isn't a skeletal muscle. It's a 'smooth' muscle. This means you don't control it like other 'skeletal' muscles - it's under the control of the autonomic nervous system. Though much smaller and thinner than the external sphincter muscle, the internal sphincter muscle plays a crucial role in maintaining perfect continence. This happens when it doesn't contract as it should. On the other hand, sometimes it can contract too much and 'go into spasm' leading to anal pain and pressure. Spasm and over contraction of the internal sphincter muscle can also contribute to other problems and is often associated with non-healing fissures. Manometry helps your doctor to sort out these specific problems.
What Can be Learned From Anorectal Manometry?
The anal and rectal area of the pelvic floor contains highly specialized muscles and neuroreceptors that regulate bowel movements. Normally, when stool enters the rectum, the anal sphincter muscle tightens to prevent passage of stool until desired. If this muscle is weak or does not contract when it's supposed to, incontinence (leakage of stool and gas) may occur.
Normally, when a
person pushes or 'bears down' to have a bowel movement, the anal sphincter
muscles relax. This will cause the pressures to decrease allowing evacuation of
stool. If the sphincter muscles tightens -- instead of relaxing -- when pushing, this could contribute to a certain type of constipation, called Obstructive Defecation.
Anal manometry measures how strong the sphincter muscles are and whether they relax as they should during passing a stool. It provides helpful information to the doctor in treating patients with fecal incontinence or severe constipation. There are many causes of fecal incontinence. Weak anal sphincter muscles or poor sensation in the rectum can contribute to fecal incontinence.
Anorectal manometry tests muscle squeeze pressure, resting pressure, and important reflexes, such as the RAIR, or rectoanal inhibitory reflex.
Is There Any Treatment?
Yes. If these abnormalities are present, they can be treated. Biofeedback techniques using anal manometry and special exercises of the pelvic floor muscles can strengthen the muscles and improve sensation. This can help treat fecal incontinence. There are other surgical and non-surgical treatments for most abnormalities of the pelvic floor, but treatment has to be individualized.
Anal Manometry and Constipation
There are many causes of constipation. Some involve sluggish movement through the whole colon, whereas others involve the anal sphincter muscles. In some patients with constipation, the anal sphincter muscles do not relax appropriately when bearing down or pushing to have a bowel movement. This abnormal muscle function may cause a functional type of obstruction. Muscles that do not relax with bearing down can be retrained with biofeedback techniques using anal manometry.
The test takes approximately 45 minutes and is not a painful procedure. The assistant will review the procedure with you, take a brief health history and answer any questions you may have. The person then lies on his left side. A small, flexible tube, about the size of a thermometer, is inserted into the rectum. During the test the nurse asks the person to squeeze, relax, and push. The anal sphincter muscle pressures are measured during each of these maneuvers. To squeeze, the person tightens the sphincter muscles as if trying to prevent anything from coming out. To push, the person strains down as if trying to have a bowel movement.