Will Colonoscopy Meet Its Match?
Screening isn't perfect, however. It just increases the odds of discovering the disease in its earliest stages when the chance of cure is greatest. Yee and colleagues cite studies showing that standard colonoscopy can still miss seeing a portion of the colon in up to 5% of cases, even when it is performed by an experienced gastroenterologist. In addition, the procedure may miss up to 20% of possibly cancerous growths.
"We consider standard colonoscopy to be the gold standard, but we have no idea how many polyps they miss," adds Amin Chaoui, MD, assistant professor of radiology at Boston University School of Medicine, in an interview with WebMD. "There have been a few studies where they had two people doing a colonoscopy back to back and found that they could miss up to 15% of polyps in the same patient, depending on how fast the colonoscopist goes." Chaoui was not involved in the UCSF study.
And although colonoscopy is generally safe when properly performed, in about 1 in 1,000 cases there is accidental perforation of the bowel wall, a potentially serious event.
Both techniques -- virtual and conventional -- also share some of the same downsides. Currently, both require the bowel to be cleansed through a regimen involving diet restrictions and high-power laxatives, a prospect that many patients find as unappetizing as the procedure itself. Some researchers are working on methods for "tagging" feces and fluids within the bowel so that the computer can then subtract them from the image, thereby getting a clean picture of the colon without the need for purging it of all contents.
But don't look for virtual colonoscopy yet in a doctor's office near you, cautions a gastroenterologist who has looked at the technique but was not involved in the current study.
"I don't think it's as accurate as colonoscopy even for the large polyps, and some of the studies have shown that this technique has a difficult time detecting flat ... polyps, which can be very dangerous and very large, but because they're flat and don't stick out into the opening of the bowel ... they tend to be missed with virtual colonoscopy," says John H. Bond, MD, chief of the gastroenterology section at the Minneapolis VA Medical Center and professor of medicine at the University of Minnesota.
"My feeling on virtual colonoscopy is that very smart people are working on it, and I think it's going to be perfected," Bond adds, "but it's still in kind of a development, experimental stage. It's important that patients understand 'Yes, this is very promising, but no, you can't go in to have it today, and if you could, you wouldn't want to just yet.'"