Is a Virtual Colonoscopy for You?

Summarized by Robert W. Griffith, MD
December 19, 2003

Introduction

It's now generally accepted that everyone over 50 should be screened at regular intervals for colorectal cancer. Colonoscopy is clearly the preferred method to be most sure of detecting any tumor, be it benign - a polyp - or a malignant cancer (see the first link, below). Colonoscopy, using a thin flexible fiber-optic tube, is able to detect over 90% of tumors, and misses only 6% of polyps smaller than 1 cm across. However, it's an inconvenient test, and the bowel-cleansing preparation is often considered worse than the procedure itself.

In 1994 an alternative to colonoscopy was first described - 'virtual' colonoscopy. This was really computed tomography used to examine the colon, a colon CT. The method has been refined and improved over the years since then. And now a large evaluation of virtual colonoscopy has been published, in which 1233 patients underwent virtual colonoscopy and conventional colonoscopy on the same day, to allow comparison of the effectiveness of the two screening methods.¹

We summarize here the Pros and Cons of virtual colonoscopy, to help you decide if you'd like to talk to your doctor about having one instead of a regular colonoscopy.

The Pros of virtual colonoscopy

• There's no need for intravenous sedation, with a 60-minute recovery period, and needing a driver to take you home.
• The whole procedure takes about 10 to 15 minutes, with another 15 to 30 minutes for interpretation of the results.
• There are no risks of bleeding or perforation of the colon wall, side effects that are reported in less than 1% of regular colonoscopies.
• Virtual colonoscopy permits the detection of abnormal conditions outside the colon (e.g. aortic aneurysms, renal and gall-bladder stones).
• In the reported study, virtual colonoscopy could detect polyps of 6 mm across or larger as accurately, or better, than conventional colonoscopy.
• Virtual colonoscopy is considerably cheaper than regular colonoscopy (but it may not be covered by health insurance - see Cons).

The Cons of virtual colonoscopy

• The same bowel-cleansing preparation is required for both procedures.
• A tube is inserted into the rectum to pump air or carbon dioxide into the colon to dilate it, which can be quite uncomfortable.
• If you are found to have a polyp of 10 mm or more across, you should have a regular colonoscopy, during which the polyp can be removed. Ideally, this would be done the same day, while the colon is still cleansed ('prepared').
• Not all centers have the experienced radiologists required to conduct and interpret the test, and it is not universally reimbursed by third-party payers (i.e. health insurance companies).

In the large published study, only 50% of the patients asked afterwards for their preference regarding future screening chose virtual colonoscopy, while 41% preferred the conventional procedure. This is probably because the latter allows suspicious lesions to be detected and removed on the same occasion.

Obviously one important deciding factor in choosing between the two methods is the likelihood that any polyps or other tumors will be found. This depends on age, heredity, and previous abnormalities detected - so that the decision will clearly be different for different individuals.

Source

• Screening virtual colonoscopy - ready for prime time? Editorial. MM. Morrin, JT. LaMont, N Engl J Med, 2003, vol. 349, pp. 2261--2264

Footnotes
1. Computed tomographic virtual colonoscopy to screen for colorectal neoplasia in asymptomatic adults. PJ. Pickhardt, JR. Choi, I. Hwang,  et al., N Engl J Med, 2003, vol. 349, pp. 2191--2200

Related Links
Time for a Colonoscopy?
How to Deal Better with Risk: The Case for Colorectal Cancer Screening (Part One of Two)

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