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Virtual Colonoscopy

Peer Review Status: Internally Reviewed
First Published: May 2004
Last Revised: May 2004

Virtual colonoscopy (also called CT colonography) was first introduced in 1994 as a new imaging method to find polyps and cancer in the colon and rectum. Virtual colonoscopy is really a CT examination of the colon with 3-D images generated by a computer. Bowel preparation, similar to a barium enema, is required. At the time of the examination, air or carbon dioxide is introduced into the bowel through a narrow tube. A medicine that will paralyze the bowel is given so the gas will stay in the abdomen while special images are taken on a CT machine or an MRI machine. It was felt this method would be more acceptable to patients because it would be less invasive and would require no sedation.

There have been many studies comparing virtual colonoscopy to conventional colonoscopy over the past 10 years. Some have shown the CT colonography to be close to conventional colonoscopy in accuracy. A recent study by researchers at the University of Michigan compared virtual colonoscopy to conventional colonoscopy in an analysis of data from 16 studies. The analysis found that virtual colonoscopy missed 27% of colorectal lesions compared with conventional colonoscopy. It was also noted that when colorectal lesions are found on virtual colonoscopy, the patient still has to undergo conventional colonoscopy to confirm the findings.
Another study at the Medical University of South Carolina looked at 600 patients at nine major clinics in the United States. The study had patients undergo virtual colonoscopy first, then conventional colonoscopy on the same day. Eight patients ultimately were diagnosed with cancer. Virtual colonoscopy missed the cancer in two of those patients.

Some researchers feel that within five years there will be better software and more sophisticated computers so that virtual colonoscopy will become just as accurate as conventional colonoscopy.

The American Cancer Society's recommended guidelines for screening for colorectal cancer are:

Beginning at age 50, both men and women should follow one of these five testing schedules:

• Yearly fecal occult blood test (FOBT)*
• Flexible sigmoidoscopy every 5 years
• Yearly fecal occult blood test plus flexible sigmoidoscopy every 5 years**
• Double-contrast barium enema every 5 years
• Colonoscopy every 10 years

*For FOBT, the take-home multiple sample method should be used.
**The combination of FOBT and flexible sigmoidoscopy is preferred over either of these two tests alone.

All positive tests should be followed up with colonoscopy.