Sigmoidoscopy vs Colonoscopy: What's the Difference?

Sigmoidoscopy vs Colonoscopy: What’s the Difference?

Doctors use a variety of endoscopy procedures to examine the colorectal system. Two of the most common types of endoscopy are sigmoidoscopy and colonoscopy. 

As you'll see in this sigmoidoscopy vs colonoscopy guide, each of these procedures plays an important role in the fight against colon cancer and other diseases.


What It Examines

During a sigmoidoscopy procedure, your doctor can see the lower part of the large intestine. In fact, since the lower section is known as the sigmoid colon, that's where this procedure gets its name. A sigmoidoscopy is also useful for viewing the rectum and the anus.

How It Works

There are two types of sigmoidoscopy. The first is flexible sigmoidoscopy, in which the doctor inserts a bendable tube into the rectum. This type is often used for more involved investigations of the sigmoid colon.

The other variety, known as rigid sigmoidoscopy, is suitable for quick, in-office examinations and preliminary investigations. For this procedure, the doctor uses a sturdy plastic or metal scope to see inside the rectum. "Proctoscope" and "rectoscope" are similar terms that are sometimes used interchangeably with "rigid sigmoidoscope."

For an example of rigid sigmoidoscopes, take a look at the disposable sigmoidoscopy kits from Adler MicroMed. These rectoscopes are available in three sizes to accommodate a variety of patients and procedures.

To perform a sigmoidoscopy, the doctor usually has a patient lie on his left side. The instrument is gently guided into the rectum. Then, with an insufflator, the doctor can introduce air to slightly expand the colon. Shining a light will help the doctor get a good view of the rectum, and procedures, such as tissue sampling, can be performed with the tube in place as well.

Who Needs It

Sigmoidoscopy is often used as an initial screening procedure for colorectal concerns since it's less invasive than a full colonoscopy. Plus, a rectoscope is just the right length for detecting problems in the rectal area.

If a patient experiences bleeding, discomfort, irregularity or other symptoms of a rectal problem, rigid sigmoidoscopy can be used for diagnostic purposes. During the procedure, the doctor may be able to identify problems like hemorrhoids or ulcers.

Polyps, tumors or other signs of colon cancer may be spotted during a sigmoidoscopy, so some doctors encourage patients to have flexible sigmoidoscopies performed at regular intervals between colonoscopies. If areas of concern are detected during a sigmoidoscopy, a follow-up colonoscopy may be ordered.

Doctors may use sigmoidoscopy to check in on a patient who is undergoing treatment for a bowel condition. An examination of the lower colon can provide some indication of whether the medication is improving the condition of the tissue.


What It Examines

One of the primary sigmoidoscopy vs colonoscopy differences is how far the doctor can see during the procedure. While sigmoidoscopy is used for investigating only the lower part of the colon, colonoscopy allows a doctor to view the colon's full length. The flexible tube used for this procedure is longer, and it's able to navigate around the colon's bends.

How It Works

Preparation for a colonoscopy is essential. Patients are usually asked to stick to a liquid diet the day before the exam and not consume anything at all after midnight. Laxative or enema treatments are used for emptying the colon as well.

Before beginning the procedure, patients are usually given a sedative. This makes the colonoscopy more comfortable.

A colonoscope, also known as an endoscope, is a long, flexible tube. The end has a light and a camera. The procedure begins like a sigmoidoscopy with the patient lying on his side in a knees-to-chest position. The thin instrument is slid into the rectum and through the colon.

Blowing air into the canal helps provide a good view of the colon walls. The camera on the endoscope sends images to a monitor in the procedure room.

You can see an example of these images in the video below:

Problem areas can often be addressed right away. For example, the doctor can use forceps to take out small polyps during a colonoscopy.

Who Needs It

The American Cancer Society recommends that patients begin regular colon cancer screenings at age 45. For patients with average risk, that usually involves getting a colonoscopy every 10 years. Sigmoidoscopies can be performed at five-year intervals between each colonoscopy.

Patients who have had previous polyps may need to get routine screenings more often than the average person. Regular colonoscopies may detect cancerous growths in time for early treatment.

Regardless of age, a patient who is experiencing colorectal symptoms may need to have a colonoscopy performed right away. With this procedure, a doctor can investigate the cause of bleeding, pain, or frequent bouts of diarrhea or constipation. The diagnosis may involve precancerous growths, colon cancer or inflammatory bowel disease.

Sigmoidoscopy vs Colonoscopy: Which Is for You?

For your colorectal care, can you opt for the less-invasive sigmoidoscopy procedure, or is a colonoscopy in order? The answer to that question will depend on your current situation.

Your doctor may recommend a sigmoidoscopy if:

  • This is an initial screening procedure.
  • Your symptoms may be caused by an anal or rectal problem.
  • You've had a colonoscopy within the last 10 years.

A colonoscopy may be needed if:

  • A sigmoidoscopy indicated that further investigation was in order.
  • You recently turned 45, or it's been 10 years since your last colonoscopy.
  • You have risk factors for colon cancer.

By alternating sigmoidoscopies and colonoscopies, you and your doctor can stay on top of your colorectal health.

As with all medical issues, your physician is the ultimate source as to what procedure best fits your needs. Discuss all options and get a second opinion if you have any doubts. These articles are intended to be a source of general information only.

Brian Chandler

Brian Chandler