Virtual colonoscopy is a minimally invasive exam to screen for cancer of the large intestine (colon). Virtual colonoscopy requires the same pre-test bowel preparation as colonoscopy. But virtual colonoscopy doesn’t require sedation or inserting a scope into the colon.
During virtual colonoscopy, a CT scan produces hundreds of cross-sectional images of your abdominal organs. The images are combined and digitally manipulated to provide a detailed view of the inside of the colon and rectum.
Virtual colonoscopy is an alternative to colonoscopy, but the new test doesn't mean you'll never have another colonoscopy. If virtual colonoscopy shows abnormalities in your colon, your doctor will typically recommend colonoscopy to learn more.
Virtual colonoscopy is used to screen for colon cancer in people who are at least 50 years old and at average risk for the disease. Studies have shown that virtual colonoscopy has detection rates similar to colonoscopy for cancer and most types of polyps. Similarly, virtual colonoscopy is as accurate as colonoscopy for people at average risk of colon cancer, including people over age 65.
Virtual colonoscopy also screens for an enlargement of the major blood vessel in the abdomen (abdominal aortic aneurysm).
Your doctor may suggest virtual colonoscopy if you:
- Are reluctant to have colonoscopy
- Are at risk for colonoscopy complications, such as excess bleeding because blood that doesn't clot normally
- Have a bowel obstruction
You aren't a candidate for virtual colonoscopy if you have:
- A history of colon cancer or abnormal tissue clumps (polyps) in your colon
- A family history of colon cancer or colon polyps
- Chronic inflammatory bowel disease (Crohn's disease or ulcerative colitis)
- Acute diverticulitis
Because virtual colonoscopy provides images of the entire abdominal and pelvic area, problems unrelated to colon cancer — such as a kidney tumor — might be found as well. Virtual colonoscopy may also be used to monitor small or very small polyps.
Insurers vary in their coverage of virtual colonoscopy. Coverage should be checked before scheduling the procedure.
Virtual colonoscopy is generally safe. Risks include:
- A tear (perforation) can occur in the colon or rectum wall due to the colon and rectum being inflated with air or carbon dioxide.
- Radiation exposure may be a concern. However, the level of radiation used during the type of CT scan in virtual colonoscopy is lower than the amount used in a diagnostic CT scan.
Before a virtual colonoscopy, you'll need to empty your colon. Any residue in your colon may obscure the images taken during the exam.
To empty your colon, follow your doctor's instructions carefully. You may be asked to:
- Follow a special diet the day before the exam. Typically, you won't be able to eat that day. Drinks may be limited to clear liquids. You may not be able to eat or drink anything after midnight the night before the exam.
- Take a laxative the night before the exam. You may also need to use a suppository to clear any remaining residue in your colon.
- Take medication to identify stool in your colon. The medication will help the doctor differentiate between colon abnormalities and stool residue.
- Adjust your usual medications. Remind your doctor of your medications at least a week before the exam. You may need to temporarily stop taking certain medications days or hours before the exam.
During the exam
You'll wear a gown, but likely no other clothes. Sedation usually isn't necessary, but you may be given medication to relax your colon.
You'll begin the exam lying on your side on the exam table, usually with your knees drawn toward your chest. The doctor will place a small tube (catheter) inside your rectum to fill your colon with air or carbon dioxide. The air or gas helps create clear images and may cause a feeling of pressure in your abdomen.
For the next part of the exam, you'll lie on your back. The exam table will be moved into the CT machine, and your body will be scanned. Then you'll turn over to lie on your abdomen or your side, and your body will be scanned again.
You may be asked to turn and hold various other positions, as well as hold your breath at times. If necessary, a contrast agent may be given through a vein in your arm to help create clearer images.
A virtual colonoscopy typically takes about 10 to 15 minutes.
In a multicenter study of people who had virtual colonoscopy to screen for colon cancer, nearly 93 percent of participants labeled their overall experience "excellent" or "good," and 93 percent indicated they would choose the procedure for their next screening.
After the exam
Most of the air or gas will be removed from your colon through the catheter in your rectum. You may feel bloated or pass gas for a few hours after the exam as you clear the remaining air or gas from your colon. Walking may help relieve any discomfort, and you can return to your usual diet and activities right away.
Your doctor will review the results of the colonoscopy and then share them with you. Your test results may be:
- Negative, if the doctor doesn't find any abnormalities in the colon. If you're at average risk of colon cancer — you have no colon cancer risk factors other than age — your doctor may recommend repeating the exam in five years.
- Positive, if the images reveal any polyps or other abnormal tissue in the colon. Depending on the size and number of polyps, your doctor may recommend a traditional colonoscopy to obtain samples of the abnormal tissue or remove the polyps. In some cases, the traditional colonoscopy or polyp removal can be done the same day as the virtual colonoscopy.
Jun. 09, 2014
- AskMayoExpert. What is computed tomography (CT) colonography? Rochester, Minn.: Mayo Foundation for Medical Education and Research; 2013.
- Kruskal JB, et al. Computed tomographic colonography. http://www.uptodate.com/home. Accessed Feb. 20, 2014.
- Yee J, et al. The time has arrived for national reimbursement of screening CT colonography. AJR. American Journal of Roentgenology. 2013;201:73.
- Pickhardt PJ, et al. Colorectal cancer: CT colonography and colonoscopy for detection — Systematic review and meta-analysis. Radiology. 2011;259:393.
- Sakamoto T, et al. Detection of flat colorectal polyps at CT screening colonography in comparison with conventional polypoid lesions. Acta Radiologica. 2012;53;714.
- Johnson CD, et al. The national CT colonography trial: Assessment of accuracy in participants 65 years of age and older. Radiology. 2012;263:421.
- Virtual colonoscopy. National Institute of Diabetes and Digestive and Kidney Diseases. http://digestive.niddk.6.gov/ddiseases/pubs/virtualcolonoscopy. Accessed Feb. 20, 2014.
- Pooler BD, et al. Screening CT colonography: Multicenter survey of patient experience, preference, and potential impact on adherence. AJR. American Journal of Roentgenology 2012;198:1361.