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by Krisha McCoy, MS

Anatomy and Physiology
Your colon, or large intestine, is a long muscular tube located in the last section of your intestines. After the stomach and small intestine digest food, the remaining material is passed through the colon, where water and electrolytes are absorbed. Formed stools are the end product of this process.

The colon is made up of: the cecum, the ascending colon, the transverse colon, the descending colon, the sigmoid colon, and the rectum.

Most of the conditions that are diagnosed or treated via colonoscopy affect the layer of cells that line the inside of the colon. A doctor can use the colonoscope to directly view this mucosal lining.

Reasons for Procedure
Conditions commonly diagnosed and/or treated with colonoscopy include: Colon cancer, colorectal polyps, colonic ulcers, colitis, or inflammation of the colon, diverticulosis.

Colorectal cancer, which initially occurs in the colon or rectum, is one of the most common types of cancer.

Essentially all colorectal cancers are believed to begin as polyps, which are abnormal growths of the mucosal lining. Detecting these polyps early is the key to preventing colorectal cancer.

In most cases, polyps cause no symptoms. colorectal cancer, however, can cause symptoms including: changes in bowel habits, blood in the stool, stools that are narrower than usual, abdominal discomfort, unexplained weight loss or fatigue.

A colonoscopy is commonly used to screen for colorectal polyps. The purpose of a screening test is to detect a problem before it causes symptoms or serious harm. If left untreated, polyps may eventually develop into colorectal cancer. Colonoscopy is also used to treat polyps by completely removing them.

In a full colonoscopy, your doctor is able to see the entire colon, from the anus to the cecum, where it connects with the small intestine. In a sigmoidoscopy, your doctor is only able to see about half that distance, to the top of the descending colon. Either technique can be used to take a sample of tissue or remove a polyp.

Other screening tests for colorectal polyps or cancer include: fecal occult blood test, which is used to identify hidden blood in the stool; barium enema, which is a series of x-rays of the colon and rectum; digital rectal exam, which is a manual examination of the rectum; virtual colonoscopy, which uses a CT scan and computer to recreate a three-dimensional image of the colon lining.

The primary disadvantage of these tests is that they cannot be used to obtain a tissue sample or remove a polyp.

If you are diagnosed with colorectal cancer, your doctor will likely advise you to have other tests, such a CT scan of your abdomen.

In the days leading up to your procedure: do not eat any solid food for 24 hours, or drink anything for 8-10 hours, before the procedure. Your doctor will recommend a preparation to clean the colon in order to make sure it is completely empty for the procedure. In addition to following a clear liquid diet, this may include taking laxatives, or performing an enema.

Also in the days leading up to your procedure: If you take medications, particularly nonsteroidal anti-inflammatory drugs such as aspirin, or blood thinners such as coumadin, ask your doctor if you need to temporarily discontinue them or change the doses. Do not start taking any new medications before consulting with your doctor. Be sure to arrange for a ride to and from the procedure.

A colonoscopy generally takes 15-60 minutes. Before the procedure, an intravenous line will be started, and you will be offered pain medication and a mild sedative to help you relax.

During the exam, you will lie on your left side with your knees bent. A colonoscopy is performed using an endoscope, which is a long, thin, flexible tube with a light and a tiny video camera attached to the end.

Your doctor will insert the endoscope into your rectum and slowly guide it to the point where your colon meets your small intestine. Your doctor will blow air through the endoscope into your colon to inflate it for better viewing.

The camera transmits an image to a TV monitor so your doctor can view the lining of your intestine.

If your doctor locates a polyp during the procedure, he or she may remove it using special instruments passed through the endoscope. The tissue obtained during this polypectomy is then sent to a laboratory for examination.

Risks and Benefits
Colonoscopy, with or without a polypectomy, is generally a very safe procedure. However, there is a chance you will experience some abdominal discomfort and/or distension. Other less common complications include: adverse reaction to medications, bleeding in the colon or rectum after a biopsy or polypectomy, a perforation, or tear, through the bowel wall, infection in the blood, heart and lung problems.

Benefits of a colonoscopy include: effective screening for colorectal cancer; both the diagnosis and treatment of colorectal polyps; diagnosis of other conditions such as colitis, or inflammation of the colorectal lining; diagnosis, and even treatment, of other causes of bleeding from the colon or rectum.

In a colonoscopy, or any procedure, you and your doctor must carefully weigh the risks and benefits to determine whether it's the most appropriate intervention for you.

After the Procedure
Colonoscopy is an outpatient procedure, so you will be able to go home after your sedative wears off, which generally takes 1-2 hours. You should receive your results over the phone, by mail, or at a follow-up appointment.

Air that is left in your intestines after the procedure may cause some persistent abdominal discomfort and bloating, which usually is resolved when the trapped air passes. If you had a polypectomy, you may feel some additional abdominal discomfort for up to five days after the procedure, but symptoms usually clear within 48 hours.

Be sure to contact your doctor if you experience: signs of infection, such as fever and chills, severe or worsening abdominal pain, rectal bleeding.


  • Colonoscopy. National Digestive Diseases Information Clearinghouse website. Available at:http://digestive.niddk.nih.gov/ddiseases/pubs/colonoscopy/index.htm. Accessed July 31, 2003.
  • Colonoscopy. National Library of Medicine website. Available at: http://www.nlm.nih.gov/medlineplus/tutorials/_instruct/instructions.html?ModuleURL=colonoscopy&LMModuleID=id149101&x=76&=20. Accessed March 3, 2004.
  • Understanding colonoscopy. American Society for Gastrointestinal Endoscopy website. Available at: www.asge.org/gui/patient/colon.asp. Accessed July 31, 2003.
  • What you need to know about cancer of the colon and rectum. National Cancer Institute website. Available at: http://www.cancer.gov/cancerinfo/wyntk/colon-and-rectum. AccessedMarch 4, 2004.

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Last Updated: Jun 2nd, 2009


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