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Virtual Colonoscopy

Computed Tomography (CT) Colonography


Updated March 12, 2013

The virtual colonoscopy is a newer screening exam used to detect colon cancer. Compared to the traditional colonoscopy, also known as the optical colonoscopy, virtual colonoscopy is less invasive and doesn't require sedation. While this sounds like a big improvement over the older method, virtual colonoscopy also has a few important drawbacks, too.

The American Cancer Society added the virtual colonoscopy, more accurately named the Computed Tomography Colonography (CTC), to the list of recommended colon cancer screening tests in 2008. The test continued to gain publicity when the President Obama underwent a CTC in 2010 for part of his routine screening examination.

CTC Versus Conventional Colonoscopy

Unlike conventional colonoscopy, where an endoscopic probe is inserted into your colon under sedation, the CTC is minimally invasive. Similar to its endoscopic counterpart, the CTC can help detect polyps and colorectal cancer with a high degree of accuracy in average-risk patients. Average-risk patients are identified as people who do not have a personal or immediate family history of cancer, irritable bowel disease (IBD) or inherited syndromes, such as familial adenomatous polyposis. People who have been treated for colon cancer will probably be encouraged to have a traditional colonoscopy, to allow for polyp visualization and removal, which can occur in one test should it be necessary. Once you have had colon polyps or cancer, your risk for recurrence is elevated.

As with traditional colonoscopy, there is a bowel preparation needed prior to the CTC (similar to the colonoscopy), to clean out and improve visibility of the lining of your colon. During the CTC, you lie on a flat table in the CT machine. A small, disposable rubber catheter is inserted into the rectum and the colon is inflated with carbon dioxide (a gas that is already present in your body). The doctor uses the CT scanner to take two or three-dimensional images of your colon while you lie in various positions. The test is complete in about five to 10 minutes.

Every screening test has risks and benefits. Learning more about these risks and benefits will help you make an informed decision when it comes to your health and screening tests. Consider the risks and benefits of CTC, then discuss them with your doctor to find out if this colon cancer screening tool is right for you.

Benefits of CTC

For average-risk patients, the myriad benefits of CTC may outweigh the risks of the conventional optical colonoscopy. As opposed to the conventional colonoscopy, the virtual colonoscopy has:

  • Low to no risk of bowel perforation
  • Low to no risk of procedural infection (the catheters are disposable in CTC, but they are sterilized and reused in conventional colonoscopy)
  • The ability to find cancers in tissue folds or above obstructions
  • The ability to visualize problems outside of the colon, such as kidney stones, hernias or gallstones
  • No sedation required; you may drive yourself to and home from the procedure
  • You return to work the same day
  • Very little discomfort
  • Less bloating or passing gas (the carbon dioxide used to inflate your colon is reabsorbed by your body)
  • No need to stop taking blood thinners, such as Coumadin (warfarin) or Plavix (clopidogrel), prior to the procedure

CTC is used as an alternative screening method for people who cannot undergo (or do not want to undergo) a conventional colonoscopy. The CTC is indicated for people who could not complete a conventional colonoscopy, who take blood thinners that cannot be weaned, or who are elderly or could suffer consequences from anesthesia.

CTC Drawbacks

Despite the many benefits of this screening exam, CTC is not for everyone. People with a history of inflammatory bowel disease, such as ulcerative colitis or Crohn’s, should not have a CTC. If you have acute colitis, a recent biopsy or polyp removal, acute diverticulitis, recent colorectal surgery or a known or suspected bowel perforation, you may be ineligible for a virtual colonoscopy. Likewise, if you have been diagnosed with colon cancer or at high risk for developing the disease, you may be encouraged to get a conventional colonoscopy.

The risks and drawbacks associated with CTC include:

  • Incidence of false positive exams
  • Many insurances (including Medicare) do not cover this exam
  • You may still require a conventional colonoscopy afterward to remove large polyps or take a biopsy
  • You still have to complete a bowel preparation prior

There are speculations that another drawback to the CTC is the radiation exposure required for the routine screening examinations every five years (a three year follow-up may be suggested for patients with larger polyps). The American Association of Physicists in Medicine mitigate this concern with their policy, the AAPM Position Statement on Radiation Risks from Medical Imaging Procedures, which states that the benefits of medical imaging (x-rays and CT scans) outweigh the risks of not having any screening.

The early detection of colon cancer saves lives; whether you choose a conventional colonoscopy or a virtual one, pick a method and get screened for colon cancer.


American Cancer Society. (September 2008). New Study Adds Weight to Virtual Colonoscopy for Average Risk Patients. Accessed January 12, 2012.

American College of Radiology. (March 2010). President Obama Gets Virtual Colonoscopy (CT Colonography) But Medicare Denies CTC Coverage to Seniors. Accessed January 10, 2012.

American Gastroenterological Association. (March 2008). The AGA Supports New Guidelines Favoring Tests That Prevent Colorectal Cancer. Accessed January 2, 2012.

Kim, D.H., Pickhardt, P.J., Taylor, A.J., et al. (October 2007). CT Colonography Versus Colonoscopy for the Detection of Advanced Neoplasia. The New England Journal of Medicine; 357. Accessed January 4, 2012.

Rabeneck, L., Paszat, L.F., Saskin, R.K., Stukel, T.A. (March 2010). Association Between Colonoscopy Rates and Colorectal Cancer Mortality. The American Journal of Gastroenterology. Accessed January 11, 2012.

U.S. Department of Health and Human Services. Centers for Medicare and Medicaid Services. (n.d.). Decision Memo for Screening Computed Tomography Colonography (CTC) for Colorectal Cancer. Accessed January 12, 2012.

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