Virtual colonoscopy

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

A 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:

• You lie on your left side on a narrow table that is connected to a CT (computerized tomography) machine.
• Your knees are drawn up toward your chest.
• A small, flexible tube is inserted into the rectum. Air is pumped through the tube to make the colon bigger and easier to see.
• You then lie on your back.
• The table slides into a large tunnel in the CT machine. X-rays of your colon are taken.
• X-rays are also taken while you lie on your stomach.
• You must stay very still during this procedure, because movement can blur the x-rays. You may be asked to hold your breath briefly while each x-ray is taken.

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

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

After the exam:

• You may feel bloated and have mild abdominal cramping and pass a lot of gas.
• You should be able to return to your regular activities.

A VC may be done for the following reasons:

• Follow-up on colon cancer or polyps
• 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 provider may recommend a regular colonoscopy instead of a VC. The reason is that a VC does not allow removing tissue samples or polyps.

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

Normal findings are images that show a healthy intestinal tract.

Abnormal test results may mean any of the following:

• Colorectal cancer
• Abnormal pouches on the lining of the intestines, called diverticulosis
• Colitis (a swollen and inflamed intestine) due to Crohn disease, ulcerative colitis, infection, or lack of blood flow
• Lower gastrointestinal (GI) bleeding
• Polyps
• Tumor

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

• No cause for bleeding or other symptoms were found. A VC can miss some smaller problems in the colon.
• Problems that need a biopsy were seen on a VC.

Risks of a VC include:

• Exposure to radiation from the CT scan
• Nausea, vomiting, bloating, or rectal irritation from medicines used to prepare for the test
• Perforation of the intestine when the tube to pump air is inserted (extremely unlikely).

The differences between a virtual and a conventional colonoscopy include:

• VC can view the colon from many different angles. This is not as easy with a regular colonoscopy.
• VC does not require sedation. You can usually go back to your normal activities right away after the test. A regular colonoscopy uses sedation and often the loss of a work day.
• VC using CT scanners expose you to radiation.
• Regular colonoscopy has a small risk for bowel perforation (creating a small tear). There is almost no such risk from a VC.
• VC is often not able to detect polyps smaller than 10 millimeters (mm). Regular colonoscopy can detect polyps of all sizes.

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

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 July 26, 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 July 26, 2024.

Patel SG, May FP, Anderson JC, et al. Updates on age to start and stop colorectal cancer screening: recommendations from the U.S. Multi-Society Task Force on colorectal cancer. Gastroenterology. 2022;162(1):285-299. PMID: 34794816 pubmed.ncbi.nlm.nih.gov/34794816/.

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.

Updated by: Michael M. Phillips, MD, Emeritus Professor of Medicine, The George Washington University School of Medicine, Washington, DC. Internal review and update on 07/26/2024 by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.