Virtual Colonoscopy
Topic Overview
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 (colorectal cancer).
Virtual colonoscopy (more accurately called computed tomography colonography, or CTC) is a new test that is being studied to determine whether the results are as accurate as a regular colonoscopy. Since virtual colonoscopy is new, it is not widely available.
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, such as a barium enema test.
- Replace a regular colonoscopy if the thin lighted microscope tube 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 eat or drink red food items such as red juice or red 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 does a virtual colonoscopy differ from a regular colonoscopy?
Virtual colonoscopy has advantages and disadvantages compared to a regular colonoscopy.
Advantages
- Virtual colonoscopy is less invasive 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.
Disadvantages
- 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.
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. However, 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 clean, you may have the regular colonoscopy the same day.
Virtual colonoscopy is not available everywhere because it requires special equipment and special training of radiologists 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 extent of your radiologist's experience 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.
 Go to top of page |  Go to next section | |
| Author: | Jan Nissl, RN, BS | Last Updated: September 1, 2006 |
| Medical Review: | Kathleen Romito, MD - Family Medicine Jerome B. Simon, MD, FRCPC, FACP - Gastroenterology | |
 | ||
| |
| Topic Contents | |
 | Topic Overview |
| Related Information | |
| Credits | |