Monday, 17 February 2014

Why CT colonography is better than PillCam

Last week, a device named PillCam was approved by the U.S. FDA, to be used for looking at the colon. I've seen blog posts comparing this to the future as predicted in The Jetsons. The idea is that the PillCam is an alternative to a traditional colonoscopy. 

But what is not being widely mentioned is that this will still require people to have full bowel preparation (which means unpleasant diarrhoea and unsafe for people with cardiac and kidney problems) because otherwise the device will simply float through a lot of faecal matter in the colon. Infact, it requires more bowel preparation than a colonoscopy, which means that the most unpleasant part of the whole experience is magnified further.

So what if you need your colon investigating but don't fancy having a colonoscopy? Is there a test which is far more pleasant and proven to work?

Yes: CT colonography, a type of CT scan specifically to look at the colon. But beware, not all CT colonography is the same. There are still plenty of centres that would require you to have full bowel preparation for the CT. 

However, the way I do perform CT colonography for my patients is (in my opinion and backed up by evidence) far more pleasant, tolerable and achieves results. I use a technique called "faecal tagging", which basically means a much much lighter way of preparing the bowel than traditional laxatives. A small volume of xray dye is taken which helps soften the stool, make it a bit more liquid, and it "paints" whatever stool is left so that it is easier to distinguish from more serious pathology on the scan. This preparation avoids the uncomfortable diarrhoea, and allows people to continue their normal activities through the preparation period.

The literature about Pillcam quotes the downsides of CT colonography as radiation and bowel perforation. The radiation dose using modern scanners and new dose reduction technology means that one CTC exam is the equivalent of 1 years worth of normal background radiation. The risk of perforation is quoted as 1 in 3-4000, very low. This can be detected easily and usually requires no further treatment.

The comparison that the manufacturers use compares PillCam with traditional methods of doing CT colonography, but times have changed and CTC should now be considered a minimally invasive, low stress examination.

When we do these scans, we can also use the data to do a "fly through" through the colon, having a similar view to a colonoscopy and the PillCam video. So this is what a "virtual colonoscopy" looks like:

I will be posting much more about CT colonography in the next few months, showing examples of the different pathologies that we look for and explaining why you may need one doing.

Dr Vikas Shah
Consultant Radiologist