Diagostics & Imaging Week’s Washington Editor

WASHINGTON — The last day of the 2007 edition of Digestive Disease Week included a number of “meet-the-professor” sessions that gave attendees an inside look at some of the issues faced by gastroenterologists.

Among these sessions was one offered by Patrick Pfau, MD, assistant professor of medicine at the University of Wisconsin Hospital (Madison), discussing how computerized tomographic colonoscopy (CTC) fares against standard colonoscopy for detection of polyps and other neoplasias.

A physician’s view of the value of CTC is shaped by one’s specialty, Pfau said, going on to acknowledge his role as gastroenterologist.

He said that there are four areas of controversy in the discussion, namely diagnostic accuracy, polyp management — generating “by far, the biggest controversy,” he said — the impact of CTC, also known as virtual colonoscopy, on standard colonoscopy and invasiveness.

Colon polyps are “very common,” Pfau said, but that very few payers are willing to cough up for screening. Part of the disincentive, he said, may be that a decade may pass between the occurrence of a polyp and the development of a cancer.

Many CTC users rely on 2D images of the colon, but software-assisted image processing can turn the 2D data sets into 3D images.

“The difference is huge,” Pfau said in reference to 3D images provided by software sold by Viatronics (Kokkola, Finland).

Are the results of CDC equivalent to endoscopy?

“Yes and no,” Pfau said, and this uncertainty is “the biggest barrier to coverage by Medicare and private insurers.”

He cited three studies commonly referenced in the CTC debate, two seeming to tilt away from CTC, with Pickhardt’s 2003 article in the New England Journal of Medicine the only of the three that used Viatronics’ software to enhance the images.

“There’s a huge bias in this literature,” Pfau said, because almost all the positive studies for CTC were conducted by radiologists, and the majority of the negative studies were written by gastroenterologists.

Pfau showed slides of 3D images of polyps in the colon, remarking that in one instance, “that’s so easy even a gastroenterologist can see it.”

He also referred to a fatigue factor in interpreting 2D images. “If you’re sitting down in a dark room ... it’s just much easier doing three-dimensional images” because the level of detail removes a tremendous amount of guesswork.

Some study data has revealed that CTC exhibits a false positive rate of about 5%, “but that’s not a horrible rate,” Pfau said. The literature suggests that CTC misses about 19% of all polyps, but the software sees polyps only larger than 10 mm. “These numbers are almost identical” to studies of scoping from about 10 years earlier.

“Clearly, colonoscopy saw more polyps, but for those larger than a centimeter, there was virtually no difference.”

CTC, he said, “is good enough for large polyps” and is “close enough” for polyps of 6-9 mm, but fails the test for polyps smaller than these.

Management of polyps is another area of interest when using CTC, and Pfau said that “most gastroenterologists take out almost all polyps.” However, he said that removing a polyp smaller than 5 mm may be too aggressive.

“Connected to every polyp is a person,” he said, adding that at 3 mm, “You’re playing a numbers game” with risk/benefit ratios that may leave the patient in the red.

Pfau said that some in the radiology community feel that a polyp smaller than 5 mm constitutes a normal exam and does not generate a report, and “the majority [of patients with 8 mm polyps] choose surveillance” over removal. He said that was not surprised by this.

“All polyps are by no means equal,” he added, and a histological examination will disclose whether the growth is cancerous. But because surgery incurs the risk of perforations and other problems, some feel it is better to wait on polyps larger than 7 mm.

“For advanced and large adenomas, there’s no difference” in the rate of removal between CTC and conventional colonoscopy, Pfau said, though CTC involves a lower rate of removal for smaller polyps.

Pfau invited the audience to offer its opinion on which procedure is more invasive, but he pointed out that “[t]here’s a lot of invasiveness with CTC because you’re putting a lot of air in there.”

One of the disincentives for doctors has to do with a medical corollary to Murphy’s Law. Depending on which study one examines, between 9% and 52% of patients will exhibit problems in nearby organs during a CTC scan, some of which will require intervention by other specialists.

“Far and away, the biggest complaint among our internists is extra-colonic findings” because it creates more work for the internist.

Virtual colonoscopy “increases patients’ options” and is “adequate in the right hands,” Pfau said. But he pointed to a variety of remaining issues, including the mode of detection changing polyp management.

“Some people get offended” when a doctor advises a patient against removing a polyp, which would be “a big change” for gastroenterologists, he said.

Pfau noted that magnetic resonance colonography is available, but that he saw the application of positron-emission technology to this procedure as the “next big step.

“I don’t think that’s anywhere near ready yet,” Pfau said, commenting further that PET has a problem with cancers of less than 1 mm. However, if PET technology can be applied to colonoscopy, “it would be a huge, huge advantage.”

Pfau told Diagnostics & Imaging Week that the pill cam “would have the same problems as CTC” because of false positives and the inability to distinguish between cancerous and non-cancerous lesions.

Pill cams also tend to tumble and cannot be manipulated to focus on a site, plus relying largely on chance to find lesions.