What is a virtual colonoscopy?
A virtual colonoscopy uses X-rays and computers (computed tomography [CT] or magnetic resonance imaging [MRI]) to take two- or three-dimensional images of the interior lining of your large intestine (colon) and rectum. A virtual colonoscopy can be used to screen for precancerous and cancerous growths in the colon or rectum (colorectal cancer), such as polyps or tumors.
Virtual colonoscopy (more accurately called computed tomographic colonography, or CTC) is still being studied to determine whether the results are as accurate as a regular colonoscopy. Virtual colonoscopy is not yet widely available.
For more information on screening tests for colon cancer, see:
Why is it done?
A virtual colonoscopy may be done to:
- Screen for colorectal cancer or polyps.
- Monitor the growth of polyps.
- Screen for recurrence of colorectal cancer in people who have had surgery for this disease.
- Evaluate abnormal results from other colon tests.
- Replace a regular colonoscopy if the thin lighted scope cannot be inserted in the colon for some reason, such as when a tumor blocks the passage.
Virtual colonoscopy is not commonly done for other conditions at this time but may prove to be useful to:
- Detect other problems or diseases of the anus, rectum, or large intestine (colon).
- Evaluate the source of internal bleeding.
- Evaluate the cause of chronic diarrhea.
- Monitor the treatment of inflammatory bowel disease.
How do I prepare for it?
Virtual colonoscopy requires the same cleansing colon prep as a regular colonoscopy. Colon prep takes 1 to 2 days depending on which type of prep your doctor recommends. For many people, the prep for a colonoscopy is more trying than the actual test. Researchers are studying methods that could be used to mark (tag) stool in the colon before virtual colonoscopy so cleansing colon preps would not be needed.
One to two days before a colonoscopy, you will need to stop eating solid foods and drink only clear liquids, such as water, tea, coffee, clear juices, clear broths, Popsicles, and gelatin (such as Jell-O). Do not drink anything red or purple, such as grape juice or fruit punch. And do not eat red or purple foods, such as grape Popsicles or cherry Jell-O.
Some preps, such as taking a prescription laxative tablet or drinking a laxative solution (such as Nulytely or Golytely), are done the evening before your colonoscopy. The colon prep causes loose, frequent stools and diarrhea so that your colon will be empty for the test. Plan to stay home during your prep time since you will need to use the bathroom frequently. The colon prep may be uncomfortable, and you may feel hungry on the clear liquid diet. If you need to drink a laxative solution, be sure to have clear fruit juices or soft drinks to drink after the prep because the solution tastes salty.
Stop drinking clear liquids 6 to 8 hours before the colonoscopy. Your doctor may have you use an enema 30 to 60 minutes before the test to completely cleanse your colon. Your doctor also may give you specific instructions before your test that take into consideration your health, age, and other medical conditions you may have.
How is it done?
Virtual colonoscopy may be done in a doctor's office, clinic, or a hospital. The test is most often done by a doctor who specializes in performing and interpreting diagnostic imaging tests (radiologist). The doctor may also have an assistant.
You will need to take off most of your clothes. You will be given a gown to wear during the test.
First, you will be asked to lie on your back. Air (or in some cases, carbon dioxide) will be used to expand your colon. This helps the doctor see all parts of your colon. The air is added using a tube placed in your anus. It may be uncomfortable when the air is put into your colon. You may be given medicine to help the muscles in your colon relax.
You will be asked to hold your breath while the pictures of your colon are being taken. If you can't hold your breath for the whole time, the doctor may need to take pictures a couple times in order to get the whole colon. You may be asked to roll over and lie on your stomach. The doctor will ask you to hold your breath again and pictures will be taken with you lying in this position.
The test usually takes about 15 to 30 minutes.
How does a virtual colonoscopy differ from a regular colonoscopy?
Virtual colonoscopy has advantages and disadvantages compared to a regular colonoscopy.
- Virtual colonoscopy is less invasive, safer, and takes less time than a regular colonoscopy.
- A thin tube to insert air into the colon is placed in the rectum rather than a long flexible tube that is moved up your colon. (However, there is usually some discomfort when the air is inserted.)
- No medication to relax or sedate you is needed, so you will be able to drive yourself home and resume normal activities.
- Virtual colonoscopy may not show polyps smaller than 10 mm (0.4 in.).
- You will need to hold your breath for short periods of time while the computed tomography (CT) scanner takes pictures of your colon. CT scanning will need to be done twice: once while you lie on your back and then again while you lie on your stomach.
- Virtual colonoscopy is not covered by all health insurance plans; check with your insurance plan before having the test.
- Virtual colonoscopy is done in the radiology department and involves a small amount of radiation exposure.
- If a polyp is found, regular colonoscopy will be needed to confirm the diagnosis and remove the polyp so it can be looked at under a microscope. If you cannot have a regular colonoscopy the same day, you will need to do another bowel preparation before the colonoscopy.
What do I need to consider about a virtual colonoscopy?
If you have an average risk for colorectal cancer, virtual colonoscopy may be an appropriate screening test for you. But if you are at an increased risk, you may require a regular colonoscopy because tissue biopsies or polyp removal can be done at the same time.
Virtual colonoscopy requires the same cleansing colon prep as a regular colonoscopy. If an abnormality is found on virtual colonoscopy, you may need a regular colonoscopy to remove and test the abnormal tissue. Since your colon is already clean, you may have the regular colonoscopy the same day.
Virtual colonoscopy is not available everywhere because it requires special equipment and special training to interpret the test. The initial evaluations on virtual colonoscopy were done by highly trained radiologists, so the results of your virtual colonoscopy may vary widely depending on the amount of experience your doctor's office or clinic has with the procedure.
Virtual colonoscopy is being studied to determine whether the results are as accurate (sensitivity) as a regular colonoscopy. More evidence is needed to show that virtual colonoscopy is a benefit in people with average risk for colon cancer and whether this screening method can prevent cancer. Colon preps that are more comfortable are also being studied.
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Other Works Consulted
- Cotton PB, et al. (2004). Computed tomographic colonography (virtual colonoscopy): A multicenter comparison with standard colonoscopy for detection of colorectal neoplasia. JAMA, 291(14): 1713–1719.
- Gupta S, et al. (2008). Variation of agreement in polyp size measurement between computed tomographic colonography and pathology assessment: Clinical implications. Clinical Gastroenterology and Hepatology, 6(2): 220–227.
- Kim DH, et al. (2007). CT colonography versus colonoscopy for the detection of advanced neoplasia. New England Journal of Medicine, 357(14): 1403–1412.
- Levin B, et al. (2003). Emerging technologies in screening for colorectal cancer: CT colonography, immunochemical fecal occult blood tests, and stool screening using molecular markers. CA: A Cancer Journal for Clinicians, 53(1): 44–55.
- Levin B, et al. (2008). Screening and surveillance for the early detection of colorectal cancer and adenomatous polyps, 2008: A joint guideline from the American Cancer Society, the U.S. Multi-Society Task Force on Colorectal Cancer, and the American College of Radiology. CA: A Cancer Journal for Clinicians, 58(3): 130–160.
- Pickhardt PJ, et al. (2003). Computed tomographic virtual colonoscopy to screen for colorectal neoplasia in asymptomatic adults. New England Journal of Medicine, 349(23): 2191–2200.
|Editor||Kathleen M. Ariss, MS|
|Associate Editor||Tracy Landauer|
|Primary Medical Reviewer||Kathleen Romito, MD - Family Medicine|
|Specialist Medical Reviewer||Peter J. Kahrilas, MD - Gastroenterology|
|Last Updated||August 11, 2008|