Deaths from colorectal cancer have begun a steady decrease since colon cancer screening was advocated by the American Cancer Society.  The screening recommendation of a colonoscopy at least once after age 50 however was one of the least favorite procedures a patient could go through.  Although the flexible colonoscope was far less obtrusive and discomforting than the traditional metal scope of years past, the inconvenience of the procedure still limited the number of people willing to undergo the screening.

Virtual imaging with CT scanning was introduced in the last decade as an alternative to invasive procedures.  The scanning uses x-rays and computers to produce two and three dimensional images of the colon from the lower end of the small intestine all the way down to the rectal area.  The images are then displayed with computer software.  Both CT and MRI scans can be used in the process.     

The idea that a scan can be used instead of an invasive procedure is one that is usually favorably received by an individual undergoing the testing.  It is obviously more comfortable, as the procedure only requires being still and holding one’s breath for a short time.  There is no sedation needed, and the testing can be scheduled during a workday, so that there is no interference with daily activities.  Traditional colonoscopy required someone to come in and drive the person home, while virtual scanning allows the individual to drive home by his or herself immediately after the procedure.  It takes less time than the traditional colonoscopy and is certainly a cleaner process.

Given the above, why isn’t this procedure the one of choice advocated by the American Cancer Society?  First, the virtual scan is more costly in most centers than the traditional colonoscopy.  Second, a CT scan does expose a patient to X-Ray radiation, even though a small amount.  Third, if something is detected on an invasive colonoscopy, it can be removed or biopsied during the same procedure.  If a scan registers a problem, the invasive colonoscopy must be scheduled anyway as a second and follow-up procedure.

Perhaps the major reason to date that the scanning has not become a side by side alternative to the invasive colonoscopy is that it is less accurate at picking up smaller lesions.  Lesions less than 2 mm in diameter may be missed on the scanning.  Doctors still debate on which polyps, even when discovered, would be immediately removed.  Most agree that those less than 5mm in diameter can safely be left until the next colonoscopy while those over 9 mm should be immediately removed.  Those in-between remain a focus of debate even among gastroenterologists, but still if a polyp is to be removed, a true rather than virtual colonoscopy must follow the original procedure.

A new study called the American College of Radiology Imaging Network National Trial (ACRIN) is due to be released in March of 2007.  It compares the results of virtual colonoscopy with invasive colonoscopy in over 2600 subjects, and at that time the American Cancer Society may comment or even recommend the virtual colonoscopy on equal footing with the traditional procedure for colon cancer screening.  While the preparation part of the procedure (using laxatives to clean the colon out before visualization) is still as tedious for each, the idea that scanning may be equivalent to the colonoscope as a diagnostic modality may have more people consent to screening for this potentially fatal disease.  That in and of itself will be a positive development for all concerned.

The information contained on this page is not intended to provide medical advice, which should be obtained directly from your physician.