Virtual Colonoscopy

What is Virtual colonoscopy?

A new X-ray test to examine the colon using a CT scanner.

What is involved?

The preparation for virtual colonoscopy is the same as for conventional colonoscopy: a clear liquid diet on the day before the procedure with powerful laxatives to clean the colon of stool.  The procedure itself involves placing a tube in the rectum and inflating the colon with gas.  The patient is then required to hold their breath while being scanned with X-rays, in a CT machine.  Scanning is performed twice; once with the patient lying on their back and once on their stomach.

Does it hurt?

Unlike conventional colonoscopy no sedation is given.   In several studies patients report that inflating the colon with gas is much more uncomfortable that having a conventional colonoscopy with mild sedation.

Is it accurate?

One study showed accuracy for detecting polyps to be equivalent to conventional colonoscopy.  Other studies have shown virtual colonoscopy to be less accurate missing 20% of colon cancers and missing potentially pre-cancerous polyps half the time.  This led expert medical researchers to conclude, "Virtual colonoscopy is not yet ready for prime time".

If a polyp or cancer is found, what happens next?

30% of patients, 50% in some studies, have polyps identified on virtual colonoscopy.   Since a conventional colonoscopy is required to remove polyps this means that many patients who have a virtual colonoscopy must repeat the bowel-cleansing regime a second time in order to have their polyps removed by conventional colonoscopy. 

Will virtual colonoscopy identify other colon diseases?

Virtual colonoscopy cannot be relied upon to diagnose ulcerative colitis, Crohn's disease or other inflammatory bowel diseases and it will not show hemorrhoids.  Therefore virtual colonoscopy should not be used to investigate rectal bleeding, abdominal pain, diarrhea or change in bowel habit.   Clinical trials of virtual colonoscopy included only patients without symptoms who were being screened for colon polyps or cancer.  These trials did not include patients with symptoms or those who have a family history of colon cancer. 

How often should virtual colonoscopy be done for screening?

Medical studies have not answered this question.

Are there risks with virtual colonoscopy?

Radiation exposure increases the risk of cancer.   The risk of cancer increases in proportion to the dose radiation to which an individual is exposed.  Whether or not the dose of radiation used in virtual colonoscopy will increase the risk of cancer is not known, however, it has been estimated that one abdominal CT scan exposes a patient to the equivalent dose of radiation as 250 chest X-rays.

Will my insurance cover virtual colonoscopy?

Medicare, Marin IPA, and most private insurance will not cover experimental procedures including virtual colonoscopy.