What Is a Colonoscopy?

Colonoscopy is a way to screen for colorectal cancer. It is the most sensitive screening test, as it can detect colorectal cancer as well as polyps, which are pre-cancerous growth. Once detected, polyps can be removed during colonoscopy, leading to cancer prevention.

In this article, we give you a quick overview of what to expect from a colonoscopy.

A colonoscopy is a visual examination that seeks to detect the presence of cancer or polyps by observing the physical appearance of the colon and rectum.

While a colonoscopy is recommended for those who are being screened for colorectal cancer, alternative and similar scope-based examinations such as a flexible sigmoidoscopy and rigid proctoscopy may also be conducted. In each of these examinations, the preparations required are largely the same, with variations only in the type of scope used.

In a colonoscopy and flexible sigmoidoscopy, a scope made up of a long, thin, flexible tube with an attached camera is inserted through the anus into the rectum and colon, and images of the large intestine lining (lumen) are visualized on a screen. These screening tests require the patient to empty their bowels beforehand. This is done by consuming a liquid diet a few days before the procedure, followed by a prescribed laxative or bowel cleansing solution the day before.

Similarly, rigid proctoscopy examines the inner lining of the rectum and anus for tumors and polyps, as well as other issues such as inflammation, hemorrhoids and bleeding. While the proctoscope shares many similarities with the colonoscope and sigmoidoscope, the tube is shorter and more rigid.

Before commencing the test, you will be asked to lie on your left side with your knees pulled up towards your chest, similar to a fetal position. The lubricated scope is inserted into the anus, and pumps air into the rectum and anus to provide an unobstructed view of the inner lining. While this may cause some discomfort, it should not be painful. You would usually be sedated to help keep you relaxed and ensure the procedure is as painless as possible.

If polyps are found, a small instrument can be inserted through the scope to remove the polyp or retrieve a sample for a biopsy. You may feel a pulling sensation or pressure, but you should not feel any pain as you would be sedated for the procedure. Small amounts of blood may be found in the stool for a few days after the test, and while serious bleeding resulting from injury to the colon and rectum may occur, it is not common.

While the procedures for colonoscopy and sigmoidoscopy are similar, there are some key differences. As the name suggests, a sigmoidoscopy does not examine the entire colon, and focuses only on the lower third of the colon, the sigmoid colon. As such, the sigmoidoscope is typically shorter than a colonoscope, and any abnormalities found during a sigmoidoscopy will still require a follow-up colonoscopy to examine the rest of the colon.

If your colorectal cancer risk is low or average, a colonoscopy is recommended every 10 years, or for a sigmoidoscopy every 5 years.