Flexible Sigmoidoscopy

This page was reviewed under our medical and editorial policy by

Toufic Kachaamy, MD, Chief of Medicine, City of Hope Phoenix

This page was reviewed on January 13, 2022.

A flexible sigmoidoscopy is a colorectal cancer screening tool used to detect irritation, swelling, ulcers, polyps and precancerous lesions. The procedure requires less time and preparation than a colonoscopy. It also doesn’t require sedation or a specialist.

Food enters the mouth and moves into the stomach, which then empties into the small intestine. The small intestine empties into the large intestine, made up of several parts:

  • Cecum, where the appendix is attached     
  • Ascending colon, which rises up the right side
  • Transverse colon, which travels under the diaphragm across the abdomen
  • Descending colon, which travels down the left side of the abdomen
  • Sigmoid colon, which forms a wide U-shape or semicircle before becoming the rectum, which attaches to the anus

During a flexible sigmoidoscopy procedure, a lighted tube is inserted through the anus and rectum into part of the colon. This flexible tube has a video camera that allows the doctor to see the inside of the sigmoid colon and check for tumors, precancerous lesions, polyps and other abnormal growths. It also has an instrument on the end that allows the doctor to take a biopsy, a sample of suspicious tissue.

Before your appointment

In preparation for a flexible sigmoidoscopy, notify your doctor about any medications you’re taking and make sure they’re OK to continue using. You'll also need to prepare the colon and rectum by emptying them completely. Colon preparation (prep) is usually done through a combination of medications and diet. Bowel prep for a flexible sigmoidoscopy isn’t generally as extensive as what’s needed for a colonoscopy.

To clean out the bowels, a doctor may recommend a clear liquid diet for the day leading up to the procedure. This means clear bouillon or broth, gelatins, coffee or tea without milk or creamer, fruit juices, sports drinks and water.

The night before the procedure, you may have to take medications to prepare the colon, a combination of laxatives and enemas that may cause diarrhea and empty the bowels.

During the procedure

A flexible sigmoidoscopy usually takes place in a doctor's office or an outpatient clinic and lasts about 10 to 20 minutes. Typically, you aren’t sedated for a flexible sigmoidoscopy.

During the procedure, you’ll be asked to lie on your left side in the fetal position. Your doctor may perform a digital rectal exam (DRE) first to check for abnormalities and prepare the anus for the scope.

The doctor then inserts a lubricated sigmoidoscope and pumps air into the colon for a better view. The doctor may also suction out fluid or waste. You may feel pressure, the urge to defecate or some slight cramping.

You may be able to see the video feed of the inside of the colon as the doctor examines it. The doctor analyzes the video for the color, texture and size of the lining of the sigmoid colon, rectum and anus.

The doctor may also remove any colorectal polyps found. You shouldn’t feel this. The doctor may study the samples in a lab to check that they aren’t cancerous or precancerous.

Procedure risks

You may experience some bleeding after the procedure, most likely if a polyp is removed. It may show up a day or two later, when you’ve taken in solid foods and are having bowel movements again.

The test may cause more serious bleeding up to two weeks after the test.

Uncommon complications of this procedure include puncturing or perforation of the colon. If you’ve experienced a puncture or perforation, the doctor may need to redo the procedure to fix it (or potentially perform surgery).

In very rare cases, these uncommon complications may be fatal. Get help right away if you have:

  • Severe pain
  • Fever
  • Continued blood in stool
  • Bleeding from the anus
  • Dizziness
  • Weakness

After the procedure

You may experience minor cramping or bloating. You may typically resume normal activities and diet immediately, unless you were sedated.

Right after (or even during) the procedure, your doctor may review the findings from the visual examination with you. It may take a few days to hear back about any tissue samples taken during the procedure.

Concerns your doctor may find during the procedure include:

  • Fissures
  • Abscesses
  • Blockages
  • Ulcers
  • Cancer or tumors
  • Polyps
  • Diverticulosis
  • Hemorrhoids
  • Inflammatory bowel disease (IBD)
  • Inflammation
  • Infection

If your doctor finds anything abnormal, he or she may recommend a colonoscopy to examine the rest of the colon and remove any polyps or growths.

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