Virtual colonoscopy (VC) is an imaging or x-ray test that looks for cancer, polyps, or other disease in the large intestine (colon).
Colonoscopy - virtual; CT colonography
How the test is performed
A virtual colonoscopy is different from a regular colonoscopy, in which a long, lighted tool called a colonoscope is inserted into the rectum and large intestine.
The test is performed in the radiology department of a hospital or medical center. No sedatives are needed and no scope is used.
You will lie on your left side on a narrow table that is connected to an MRI or CT scan machine.
- Your knees will be up toward your chest. A small, flexible tube will be inserted into your rectum. Air is pumped through the tube to make the colon bigger and easier to see.
- After this is done, you will be asked to lie on your back.
- Next, the table slides into a large tunnel through the machine, where x-rays create images of your colon.
- You must stay very still during this procedure, since movement can blur the pictures. You may be asked to hold your breath briefly while each picture is taken.
A computer combines all the images to form three-dimensional pictures of the colon, which are viewed on a video monitor.
Pictures are also taken while you lie on your stomach.
How to prepare for the test
Everyone undergoing any type of colonoscopy must completely empty their bowels before the exam. This may be done using an enema or laxatives combined with a liquid diet the day before the test. The bowel must be completely emptied until no solid matter remains.
Unfortunately, diarrhea is common during preparation. Drink plenty of clear liquids, such as apple juice and chicken broth, to avoid dehydration.
Make sure you tell your health care provider about any medications you are taking. You will be told which you can take, and which you should temporarily stop. CT and MRI scanners are very sensitive to metals. Do not wear jewelry the day of your exam. You will be asked to wear a hospital gown for the procedure.
How the test will feel
The x-rays are painless. Pumping air into the colon can create cramping or gas pains.
Why the test is performed
Virtual colonoscopy may be performed to:
- Follow-up on colon cancer or polyps
- Look for the cause of:
- Abdominal pain, changes in bowel movements, or weight loss
- Anemia due to low iron
- Blood in the stool or black, tarry stools
- Screen for cancer of the colon or rectum (should be done every 5 years)
Your doctor may want to do a conventional colonoscopy instead of a virtual colonoscopy. The reason is that virtual colonoscopy does not allow the doctor to remove tissue samples or polyps.
Other times, a virtual colonoscopy is done if your doctor was not able to move the flexible tube all the way through the colon during a conventional colonoscopy.
Normal findings are images of a healthy intestinal tract.
What abnormal results mean
A regular colonoscopy may be done (on a different day) after a virtual colonoscopy if:
- No cause for bleeding or other symptoms were found. Virtual colonoscopy can miss some smaller problems in the colon.
- Problems that need a biopsy were seen on a virtual colonoscopy
What the risks are
Risks of virtual colonoscopy include:
- Exposure to radiation from the CT scan
- Medicines used to prepare for the test can cause nausea, vomiting, bloating, or rectal irritation.
Differences between virtual and conventional colonoscopy include:
- Virtual colonoscopy can view the colon from many different angles. This is not as easy with conventional colonoscopy.
- Virtual colonoscopy does not require sedation. You can usually go back to your normal activities right away after the test. Conventional colonoscopy uses sedation, and usually the loss of a work day.
- Virtual colonoscopy using CT scanners expose you to radiation.
- Conventional colonoscopy has a small risk of bowel perforation. There is virtually no risk from virtual colonoscopy.
Burt RW, Barthel JS, Dunn KB, David Ds, Drelichman E, Ford JM, et al. NCCN clinical practice guidelines in oncology. Colorectal cancer screening. J Natl Compr Canc Netw. 2010;8:8-61.
Bresalier RS. Colorectal cancer. In: Feldman M, Friedman LS, Brandt LJ, eds. Sleisenger and Fordtran's Gastrointestinal and Liver Disease. 9th ed. Philadelphia, Pa: Saunders Elsevier; 2010:chap 123.
Last reviewed 10/8/2012 by George F. Longstreth, MD, Department of Gastroenterology, Kaiser Permanente Medical Care Program, San Diego, California. Also reviewed by A.D.A.M. Health Solutions, Ebix, Inc., Editorial Team: David Zieve, MD, MHA, David R. Eltz, and Stephanie Slon. 10/08/12
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