FEATURE


are concerned about taking a prep for a colonoscopy,” Johnson says. “To be kept in mind, however, is this doesn’t mean that for the procedure there is not some ingestion. It is not truly prep-less because people still have to ingest con- trast material for several days before they get their test, and that involves the patient’s compliance with repetitive in- gestion of the barium tablets or liquid before they get their CTC.


“The acceptance of the patients for Assessing Virtual Colonoscopy


Laxative-free CT colonography might be easier on patients in some ways than the traditional procedure, but it is not necessarily a viable alternative. BY ROBERT KURTZ


I


n May 2012, the Annals of Internal Medicine published a study on the


performance of laxative-free, computer- aided computed tomographic colonog- raphy (CTC) for colon screening. CTC, also known as “virtual colonoscopy,” uses CT scans or, less often, magnetic resonance imaging of the large intestine to generate images that a computer puts together to create an animated, three- dimensional view of the inside of the large intestine. The procedure is intend- ed to allow clinicians to look for signs of precancerous polyps. The laxative-free CTC replaces patient ingestion of a laxative with ingestion of a contrast agent, which is designed to mark stool and distin- guish it from the colon when examin- ing images. The study’s researchers concluded that the results of the study could sug- gest “a possible role for laxative-free CTC as an alternate screening meth-


16 ASC FOCUS MARCH 2013


od.” The mainstream media provided extensive coverage of the study, of- ten playing up laxative-free CTC as a possibly more comfortable and, at times, equally effective alternative to colonoscopy. Is the hype generated by the study and supported by the media justified? Should ASCs and gastroenterology centers consider offering this proce- dure in place of or as an alternative to traditional colonoscopy? To answer these questions, it’s im-


portant to understand some of the his- tory of CTC, says David A. Johnson, MD, professor of medicine and chief of gastroenterology at the Eastern Virginia Medical School in Norfolk, Virginia, and past president of the American College of Gastroenterol- ogy (ACG). “To give perspective, the prep- less or laxative-free CTC is really the golden chalice because most people


CTC, when looked at, has been mixed, and certainly not overwhelmingly in favor of CTC over colonoscopy, pri- marily because patients have some dis- comfort with the procedure,” Johnson continues. “They get air insufflated in their rectum and there’s no medication, whereas with colonoscopy they do re- ceive medication and people usually don’t even remember the procedure.” Patients aren’t the only ones who


have been hesitant to embrace CTC; the federal government has been as well. In 2008, the American College of Radiology Imaging Network (ACRIN) published the results of a national CTC trial in the New England Journal of Medicine. This was the largest CTC screening trial in the US, Johnson says. The results indicate that for detecting polyps sized 10 millimeters (mm) or larger, virtual colonoscopy detected 90 percent of polyps identified by stan- dard optical colonoscopy. For polyps 6–9 mm, however, virtual colonoscopy was even less reliable than standard colonoscopy, detecting 78 to 87 per- cent. For polyps 5 mm and smaller, which constitute about 80 percent of all precancerous polyps in the colon, CTC is unreliable. There is also some debate about whether virtual colonos- copy misses depressed or “flat” polyps. “The data that came from that


ACRIN trial pretty much put the nail in the coffin as far as it being approved by the U.S. Preventive Services Task Force,” Johnson says. “That led the Centers for Medicare & Medicaid Ser- vices (CMS) to come out independently


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