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 in the lower part of the large intestine, or colon.

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.

Flexible sigmoidoscopy vs. colonoscopy

A flexible sigmoidoscopy is a less invasive variation of a colonoscopy, because it checks only the lower third of the colon and uses a shorter, flexible tube. Doctors may first recommend a stool test or sigmoidoscopy, then follow up with a colonoscopy if anything abnormal is detected. 

A flexible sigmoidoscopy also differs from a colonoscopy in that:

  • It requires less time and preparation
  • It doesn't require sedation
  • It doesn't have to be administered by a specialist

Flexible sigmoidoscopy prep

In preparation for a flexible sigmoidoscopy, the patient should notify the care team about any current medications and make sure they’re OK to continue using. The patient also needs 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, the patient 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, the patient isn't sedated for a flexible sigmoidoscopy.

During the procedure, the patient will be asked to lie on his or her left side in the fetal position. The care team 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. The patient may feel pressure, the urge to defecate or some slight cramping.

The patient 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. The patient shouldn’t feel this. The doctor may study the samples in a lab to check that they aren’t cancerous or precancerous.

Flexible sigmoidoscopy risks and side effects

Patients may experience some bleeding after the procedure, most likely if a polyp is removed. It may show up a day or two later, when patients have taken in solid foods and have 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 the patient experiences 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 any of the following occur: 

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

After the procedure

Patients may experience minor cramping or bloating. Most patients may typically resume normal activities and diet immediately, unless sedation was used.

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

What can a flexible sigmoidoscopy detect?

Concerns the care team may find during the procedure include:

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

If the care team finds anything abnormal, a colonoscopy may be recommended to examine the rest of the colon and remove any polyps or growths.

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