Virtual colonoscopy

Definition

Virtual colonoscopy (VC) is an imaging or x-ray test that looks for cancer, polyps, or other disease in the large intestine (colon). The medical name of this test is CT colonography.

Alternative Names

Colonoscopy - virtual; CT colonography; Computed tomographic colonography; Colography - virtual

How the Test is Performed

VC is different from regular colonoscopy. Regular colonoscopy uses a long, lighted tool called a colonoscope that is inserted into the rectum and large intestine.

VC is done in the radiology department of a hospital or medical center. No sedatives are needed and no colonoscope is used.

The exam is done as follows:

A computer combines all the images to form three-dimensional pictures of the colon. The radiologist can view the images on a video monitor.

How to Prepare for the Test

Your bowels need to be completely empty and clean for the exam. A problem in your large intestine that needs to be treated may be missed if your intestines are not cleaned out.

Your health care provider will give you the steps for cleansing your bowel. This is called bowel preparation. Steps may include:

You need to drink plenty of clear liquids for 1 to 3 days before the test. Examples of clear liquids are:

Keep taking your medicines unless your health care provider tells you otherwise.

You will need to ask your provider if you need to stop taking iron pills or liquids a few days before the test, unless your provider tells you it is OK to continue. Iron can make your stool dark black. This makes it harder for the radiologist to view inside your bowel.

CT and MRI scanners are very sensitive to metals. Do not wear jewelry the day of your exam. You will be asked to change out of your street clothes and wear a hospital gown for the procedure.

How the Test will Feel

The x-rays are painless. Pumping air into the colon may cause cramping or gas pains.

After the exam:

Why the Test is Performed

VC may be done for the following reasons:

Your provider may recommend a regular colonoscopy instead of a VC. The reason is that VC does not allow removing tissue samples or polyps.

Other times, a VC is done if a regular colonoscopy could not be completed.

Normal Results

Normal findings are images of a healthy intestinal tract.

What Abnormal Results Mean

Abnormal test results may mean any of the following:

Regular colonoscopy may be done (on a different day) after a VC if:

Risks

Risks of VC include:

Considerations

Differences between virtual and conventional colonoscopy include:

References

Garber JJ, Chung DC. Colonic polyps and polyposis syndromes. In: Feldman M, Friedman LS, Brandt LJ, eds. Sleisenger and Fordtran's Gastrointestinal and Liver Disease: Pathophysiology Diagnosis Management. 11th ed. Philadelphia, PA: Elsevier; 2021:chap 126.

Kim DH, Pickhardt PJ. Computed tomography colonography and evaluation of the colon. In: Gore RM, Levine MS, eds. Textbook of Gastrointestinal Radiology. 5th ed. Philadelphia, PA: Elsevier; 2021:chap 38.

National Cancer Institute website. Colorectal cancer prevention (PDQ) - health professional version. www.cancer.gov/types/colorectal/hp/colorectal-prevention-pdq. Updated August 18, 2023. Accessed February 11, 2024.

National Comprehensive Cancer Network website. NCCN clinical practice guidelines in oncology (NCCN guidelines): colorectal cancer screening. Version 1.2024 - February 27, 2024. www.nccn.org/professionals/physician_gls/pdf/colorectal_screening.pdf. Updated February 27, 2024. Accessed April 17, 2024.

Shaukat A, Kahi CJ, Burke CA, Rabeneck L, Sauer BG, Rex DK. ACG clinical guidelines: colorectal cancer screening 2021. Am J Gastroenterol. 2021;116(3):458-479. PMID: 33657038 pubmed.ncbi.nlm.nih.gov/33657038/.

US Preventive Services Task Force website. Final recommendation statement. Colorectal cancer: screening. www.uspreventiveservicestaskforce.org/uspstf/recommendation/colorectal-cancer-screening. Published May 18, 2021. Accessed February 11, 2024.


Review Date: 1/31/2023
Reviewed By: Michael M. Phillips, MD, Emeritus Professor of Medicine, The George Washington University School of Medicine, Washington, DC. Internal review and update on 02/10/2024 by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.
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