Virtual colonoscopy/CT colon/colonography

A CT Colon is a computerized x-ray of the colon.  It has been in existence for only a few years but is rapidly replacing the older, less accurate ‘barium enema’ colon x-ray, although it does use about twice the amount of radiation than the barium enema.  CT Colon is not as accurate as a colonoscopy, it exposes the patient to radiation, it involves a bowel preparation just like colonoscopy, and if something is seen in the colon nothing can be done about it – the patient will have to go for a colonoscopy at a later date – and that will entail another bowel preparation.  For those patients with family histories of colon cancer and who are going to need regular colon examinations throughout their lives, particularly the younger ones, the radiation element of repeated CT Colon examinations is an issue.

Having listed all of these negatives, we have to say that CT Colon is actually a very useful test for certain patients and we do refer quite a lot of people for a CT Colon. The patients we refer for CT Colon are those that should not or cannot or would rather not colonoscope.  Such patients include the frail individual whom we would rather not expose to sedation, and patients in whom we cannot complete colonoscopy because of technical factors such as excessive angulation of the colon.  Sedation is not used in CT Colon and so for the frail patient that may make things a bit simpler, although not always.  It is a good choice for those who might be allergic to sedation.  In addition, CT Colon should result in fewer colon injuries than colonoscopy simply because there is no long tube going into the colon.  The CT Colon does require that some air be pumped into the colon through a small tube inserted in the rectum, and perforations of the colon have occurred from this in CT Colon procedures, but this should be very rare.

Another nice bonus of the CT Colon is that it does provide some information about the other organs in the abdomen, albeit not with the same clarity as when a standard abdominal CT scan is ordered, since the CT Colon is optimized primarily to view the colon.  If we want to assess the colon but are suspicious there may be a problem in another organ instead or as well, we might refer that patient for a CT Colon rather than doing a colonoscopy.

CT Colon is not particularly accurate for polyps under 0.6 cm, and has trouble assessing the sigmoid colon if there are many diverticulae there since the CT Colon requires that the colon be distended with air, and areas of diverticular often will not distend due to bowel wall thickening and spasm.  Currently, CT Colon is not recommended for colorectal cancer screening in patients with a significant family history of colorectal cancer (first or second degree relative) or for those with a positive FIT or fecal occult blood test.

The Pezim Clinic performed most of the polypectomies of the first CT Colon examinations undertaken in the lower mainland of BC and was part of the first report of the CT Colon experience in British Columbia, published in the British Columbia Medical Journal.  Many of these procedures were done later in the same day, saving the patient from having to undergo a second bowel prep.

As with all new investigations, it will take some years before the true value of CT Colon is known.  For the present time it is important that patients who wish to have a one should ensure that the facility has an established program with high-level equipment and experienced CT Colon radiologists.  Ideally, the facility should also have an arrangement with a colonoscopy clinic to allow same-day colonoscopy when biopsy or polyp removal is necessary, thus avoiding an additional bowel preparation.

© Pezim Clinic, Vancouver, British Columbia, Canada