Houston Methodist. Leading Medicine.
Houston Methodist. Leading Medicine

Colorectal Testing

Colorectal Testing

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The Methodist Center for Restorative Pelvic Medicine
6550 Fannin Street
Houston, TX 77030
713-791-5023 fax
Maps & Directions

In 2011, the American Cancer Society estimated more than 141,000 new cases of colorectal cancer would be diagnosed. Colorectal cancer is the third leading cause of cancer deaths in both men and women in the United States. Methodist physicians recommend that any person over the age of 50 should be screened for colorectal cancer, especially males and those with a personal or family history of the disease.

Methods of Testing

Anorectal Ultrasound

An anorectal ultrasound, or ultrasound of the anus, is used to determine the nature of an injury to the sphincter muscle. The sphincter muscle is a small circular muscle found at the end of the anal cavity that keeps the anal canal closed. Injury to the muscle can result in loss of bowel control or the presence of a fistula.

During this relatively painless test, a smooth probe about the diameter of the index finger is placed in the rectum to take pictures of the wall of the anus using sound waves. The sound waves bounce off the walls of the tissues to make echoes. The echoes are then transmitted onto a screen where your physician can inspect suspicious lesions.

The procedure lasts about 10 minutes. Prior to the procedure, patients are required to clean out the rectum using enemas or laxatives as instructed by the physician.

Anal Manometry

Patients experiencing difficulty with constipation or incontinence (loss of bowel control) may undergo an anal manometry test. This simple diagnostic test uses various squeezing and resting reflexes to measure pressures in the anal cavity and anal sensation. During the procedure, a plastic tube with a balloon on the end is inserted into the rectum and inflated to measure a reflex. The test measures changes in the pressure of water dripping into the tube. The tube is then removed from the anus to obtain the readings.

Anal manometry usually takes about 30 minutes to complete. Prior to the procedure patients are required to clean out the rectum using enemas or laxatives as instructed by the physician.


Defecography, also known as evacuation proctography, is used to determine proper treatment options for chronic constipation, rectal prolapse, rectocele (an out-pouching of the rectum), fecal incontinence or anismus (inappropriate spasm of the anal sphincter - a ring sized muscle located at the end of the anal cavity that keeps the anal canal closed).

This procedure, although uncomfortable, is an essential tool to help doctors evaluate the pelvic floor muslces and rectum while a patient is having a bowel movement. The patient is seated in a special chair that allows X-rays of the pelvis to be taken. The X-rays are taken in different positions: while the patient is at rest, straining, squeezing and during defection. During the test, barium paste is given in the form of an enema. The paste is visible within the rectum on the X-rays, showing the details of the small intestine. Any problems with pelvic floor relaxation can be seen on the X-ray.

The entire test should take about 30 minutes to complete. The patient’s privacy and discretion is ensured by The Methodist Hospital and the Center for Restorative Pelvic Medicine accommodates the patient’s needs as much as possible.

Pudendal Nerve Testing

Pudendal nerve testing is conducted to determine whether the pudendal nerve, found in the pelvis, is functionally normally. A dysfunctional pudendal nerve can lead to incontinence or loss of control when passing gas or stool. The test will indicate whether there is a delay between the time the nerve senses stimulation, and when the nerve actually sends a message to the sphincter muscle.

During the procedure, the patient lies on their side and bends at the knees. A technologist performs the test by placing an electrode grounding pad (like an EKG pad) on the thighs and/or buttocks. Another electrode is placed on the technologist’s index finger. The finger with the electrode is gently inserted into the rectum. A mild, painless electrical stimulus is sent through the electrode to the pudendal nerve, causing the muscles on the thighs and/or buttocks to twitch. The same stimulus is sent to the right and left branch of the nerve. The patient’s bodily response to the stimulation is recorded and interpreted by a physician to determine whether there are any nerve conduction delays.

The procedure will take approximately 15 to 20 minutes to complete and results are usually determined within an hour.