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Sunday, March 29, 2009

Virtual Colonoscopy-A Primer

Virtual Colonoscopy-What You Need to Know

Note: The Colonoscopy Chronicles attempts to provide information that is as accurate as possible. It is not intended as medical advice. You should consult your personal physician regarding your own medical condition.

So called “virtual colonoscopy” has generated a lot of buzz lately. This is probably because most of us baby boomers fancy ourselves as being a little “tech savvy”, and at the same time are at an age when we have to think about colon cancer screening. Thus, “virtual colonoscopy” would seem like the “perfect storm”- a way to do the right thing, and at the same time use sleek new technology to avoid the indignity of a conventional “optical”colonoscopy. Well, as they say, if it sounds too good to be true, it probably is!

Don’t get me wrong, virtual colonoscopy is definitely an excellent addition to the arsenal of tools we have available for colorectal cancer screening. However, it has to be placed in proper perspective. Virtual colonoscopy is also known as computerized tomographic colography(CTC). For sake of simplicity, I will refer to it as CTC the rest of the way. Well, for starters, what is CTC? Essentially, CTC is a CT scan of the abdomen and pelvis using specialized software that provides detailed images of the colon. A CT scan is a type of x-ray that involves placing the patient in a machine with a flat table, and a doughnut shaped ring that surrounds the area of the body being scanned. In order for CTC to be done properly, the patient has to take a laxative preparation prior to the procedure(just like for conventional colonoscopy). Furthermore, a small tube is placed into the patient’s rectum to inflate the colon with air for optimal results-sometimes a rather uncomfortable maneuver-since the patient is not given anesthesia.

I think you are getting the picture that virtual colonoscopy is not quite as virtual as you might have thought. It’s not like you just e-mail your information to the radiologist and you get a nice little printout of the results without ever having to step foot into the hospital!! The fact is, the aspect of conventional colonoscopy that tends to aggravate patients the most-the laxative cleanout-is still necessary with CTC.

OK, well then, let’s say it is not quite so virtual. But you’re still interested, because you like to be on the edge of technology. Due to your busy schedule, you don’t want to be sedated for a conventional colonoscopy, which would require that you do not work or drive for the remainder of the day. You want to come in, get your CTC, then head off to the health club and Starbuck’s-right? Understandable. But consider this-what if CTC shows a polyp-a potentially precancerous lesion that will need to be removed via conventional colonoscopy? There would be two options in this situation:
1-Proceed directly to conventional colonoscopy that same day(requiring that you have pre-arranged a ride home. Forget about Starbucks+health club)
2-Arrange conventional colonoscopy for a later date. The downside here is that you would have to repeat the laxative preparation prior to the conventional colonoscopy-again, the aspect that patient’s find the most distasteful.

Well, despite these somewhat confusing logistical issues, you are still fired up for the CTC. The next question to tackle is, how accurate is CTC? This is a question that I could discuss for hours, but I’ll try to distill it into a single sentence: CTC seems generally pretty accurate. It is up to about 95% accurate for discovering polyps greater than 10 millimeters(mm). While some studies have shown a significantly lower detection rate, I think that the bulk of the evidence is that CTC is quite accurate for detecting these larger polyps. Conventional colonoscopy is not 100% accurate for detecting polyps greater than 10 mm, but is more accurate than CTC. As far as detecting polyps less than 10mm, conventional colonoscopy is dramatically better. Does this matter? This is a subject of great debate. Clearly, polyps greater than 10mm are the ones more likely to contain cancer cells, or if not already cancerous, to transform into cancer. So clearly these polyps are more significant than polyps less than 10mm. However, a certain percentage of even these small polyps can contain cancer cells, or transform into cancer.

You, the unapologetic baby boomer, are still enthused about CTC, despite some of its imperfections. The next question is, what about the safety of the exam. CTC is extremely safe. There is radiation exposure involved, which should not be completely dismissed. Furthermore, the American Cancer Society guidelines for colorectal cancer screening(just updated in 2008) advise CTC every 5 years as opposed to every 10 years for conventional colonoscopy. The significance of this radiation exposure every 5 years in a person starting at age 50 and expected to live to at least 75 is not clear. On the other hand, assuming nothing is detected on CTC, the patient avoids the potential hazards of conventional colonoscopy-which, although rare, do exist-including risk of perforation, bleeding, and anesthetic risks.

Now, the quintessential question on a baby boomer’s mind-will insurance cover it? Aha, when the rubber meets the road, we want our technology, but do we want to pay for it? Although CTC has been endorsed by the American Cancer Society as an acceptable colorectal cancer screening alternative, Medicare and most third party payers will not cover screening CTC. This is not likely to change in the near future, since Medicare recently came out with their position-CTC will not be covered for screening. So, unless you are willing to pay out of pocket-it is likely that you will choose conventional colonoscopy- rather than CTC, since the cost of conventional colonoscopy is generally covered by Medicare and most third party payers.

If you choose to have a CTC to evaluate your colon, rather than conventional colonoscopy, I would suggest the following advice:

1. Go to a center that has a reasonable amount of experience in the CTC and a radiologist who has a special interest and training in the procedure

2. Make sure that the center where you do the CTC has a system in place to

a. Read the x-rays promptly
b. Have it arranged so that if a polyp or other abnormality is seen on CTC, you can be assured that a gastroenterologist is available to do a conventional colonoscopy the same day-so you do not have to go through the laxative cleanout process a second time. I would emphasize that you will have to have someone on standby to drive you home in case you should need to have the conventional colonoscopy.

It is worth having a frank, detailed discussion with your physician to see if CTC is a good option in your particular community, as the availability and quality of CTC may vary tremendously. Whether you choose virtual or conventional colonoscopy, make sure you get appropriate colon cancer screening so we can reduce the death rate from the number two cancer killer in America!

1 comment:

blackrock said...

Hey Dr. Mike,
I appreciate your nice summary of VC. The radiation exposure combined with poor detection of polyps smaller than 10cm concern me most. With the prep involved with VC, why not just get the colonoscopy?

What are your thoughts on the stool-based DNA screening test that was added to the ACS Screening Guidelines (it was added to guidelines at the same time as VC)? It seems like this DNA test is a big improvement over FOBT/FIT in terms of sensitivity and specificity. And no prep is involved. If the DNA test comes up positive, you can then get a colo. I would appricate your opinion in this area.