A flexible sigmoidoscopy is a medical test used to evaluate the lower part of the large intestine (colon). During a flexible sigmoidoscopy exam, a thin, flexible tube (sigmoidoscope) is inserted into the rectum.
A tiny video camera at the tip of the tube allows the doctor to view the inside of the rectum and most of the sigmoid colon — about the last two feet (61 centimeters) of the large intestine. If necessary, tissue samples (biopsies) can be taken through the scope during a flexible sigmoidoscopy exam.
Flexible sigmoidoscopy doesn't allow the doctor to see the entire colon. As a result, any cancer or polyps farther into the colon can't be detected with flexible sigmoidoscopy alone.
Why is it done?
The doctor may recommend a flexible sigmoidoscopy test to:
- Investigate intestinal signs and symptoms. A flexible sigmoidoscopy exam can help the doctor to explore possible causes of abdominal pain, rectal bleeding, changes in bowel habits, chronic diarrhea and other intestinal problems.
- Screen for colon cancer. If one is at age of 50 or older and he is having no colon cancer risk factors other than age — which puts him at average risk — the doctor may recommend a flexible sigmoidoscopy exam every five year to screen for colon cancer.
Sigmoidoscopy is one option for colon cancer screening, but there are other options that allow visualization of the whole colon.
What are the various risks associated with it?
A flexible sigmoidoscopy exam poses few risks. Rarely, complications of a flexible sigmoidoscopy exam may include:
- Bleeding from the site where a tissue sample (biopsy) was taken
- A tear in the colon or rectum wall
How to prepare for the procedure?
Before a flexible sigmoidoscopy exam, the patient will need to clean out (empty) colon. Any residue in the patient’s colon may obscure the view of his colon and rectum during the exam.
To empty the patient’s colon, follow the doctor's instructions carefully. The patient may be asked to:
- Follow a special diet the day before the exam - Typically, the patient won't be able to eat the day before the exam. Drinks may be limited to clear liquids — plain water, broth, carbonated beverages, and tea and coffee without milk or cream.
- Take a laxative the night before the exam - The laxative will be in either pill or liquid form.
- Use an enema kit. In some cases, the patient may need to use an over-the-counter enema kit — either the night before the exam or a few hours before the exam — to empty the colon or the patient may be asked to take two enemas at home the morning of the procedure.
- Adjust the medications - Remind the doctor of the patient’s medications at least a week before the exam — especially if he is having diabetes, if he takes medications or supplements that contain iron, or if he takes aspirin or other blood thinners. The patient may need to adjust his dosages or stop taking the medication temporarily.
What can be expected from the process?
During the exam
Wearing a gown, the patient will begin the exam lying on his side on the exam table, usually with the knees drawn toward the chest. The doctor will insert a sigmoidoscope into the patient’s rectum.
The sigmoidoscope contains a light and a tube (channel) that allows the doctor to pump air into the patient’s colon. The air inflates the colon, which provides a better view of the colon lining. When the scope is moved or air is introduced, the patient may feel abdominal cramping or the urge to move his bowels.
The sigmoidoscope also contains a tiny video camera at its tip. The camera sends images to an external monitor so that the doctor can study the inside of the patient’s colon. The doctor can also insert instruments through the channel to take tissue samples (biopsies).
A flexible sigmoidoscopy exam typically takes about 15 minutes. It may require slightly more time if biopsies are taken. Sedation and pain medications usually aren't necessary. If a polyp is found, the doctor will likely recommend a full colonoscopy to look at the patient’s whole colon.
What are the expected results?
The doctor will review the results of the flexible sigmoidoscopy exam and then share the results with you.
- Negative result - A flexible sigmoidoscopy exam is considered negative if the doctor doesn't find any abnormalities in the colon. If the patient is at average risk of colon cancer — he has no colon cancer risk factors other than age — the doctor may recommend waiting for five years and then repeating the exam.
- Positive result - A flexible sigmoidoscopy exam is considered positive if the doctor finds polyps or abnormal tissue in the colon. Depending on the findings, the patient may need additional testing — such as a colonoscopy — so that any abnormalities can be examined more thoroughly, biopsied or removed. During a colonoscopy, the doctor can also screen the entire colon for other abnormalities.
How much of the patient’s colon and rectum can be viewed during a flexible sigmoidoscopy depends on the experience of the doctor doing the patient’s test and the success of the colon preparation.
If the doctor is concerned about the quality of the view through the scope, he or she may recommend a repeat flexible sigmoidoscopy exam or another screening test.