Researchers Test Laxative-Free Colon Scan

MONDAY, May 14 (HealthDay News) -- A preliminary new study suggests that patients who get virtual colonoscopies -- alternatives to regular colonoscopies -- might avoid the unpleasant task of bowel-cleansing with laxatives beforehand.

However, this study of 605 people found that the laxative-free virtual colonoscopies were less effective at detecting small malignancies than regular colonoscopies. Not surprisingly, patients who underwent the laxative-free procedure preferred it.

"This study opens the door to a more patient-friendly form of exam," said study lead author Dr. Michael Zalis, associate professor of radiology at Harvard Medical School. "We know that the colonoscopy preparation keeps a lot of people from participating."

Colon cancer is expected to kill 50,000 people in the United States this year. Colonoscopy screening enables doctors to identify and remove precancerous polyps.

The virtual colonoscopy has become more common in recent years. The American Cancer Society endorses it as an acceptable screening method. Supporters say it is more comfortable than regular colonoscopy because it doesn't require placing a fiber-optic scope into the rectum. Instead, doctors use CT scanners to inspect the intestines for signs of colon cancer.

The virtual procedure doesn't require sedation, unlike regular screening, but it does require insertion of a small tube into the rectum to push carbon dioxide into the intestine.

And like regular colonoscopy, virtual colonoscopy usually requires that patients drink a liquid laxative that causes diarrhea and cramping as it cleanses the bowel of fecal matter.

But this new procedure cleanses the bowel "electronically." Patients involved in the study, who were 50 to 85 years old and at average to moderate risk of colon cancer, received a "contrast agent" to add to low-fiber meals and snacks for two days before their procedures. Then they had virtual colonoscopies without needing to take laxatives.

Contrast agents are designed to mark things in the body so radiologists can detect them. In this case, the contrast agents marked bits of feces in the intestines, and a software program removed them from the image.

Several weeks later, the patients underwent regular colonoscopy, and the researchers compared the results.

The researchers found that the laxative-free colonoscopies were nearly as good as regular screenings at identifying polyps 10 mm or larger -- the most likely to become cancerous -- but were less effective at detecting smaller polyps. Common practice usually involves removing any polyps 6 millimeters or larger, the study authors said.

The virtual procedures do "an OK but not great job at finding larger polyps that everybody would agree need to be identified," said Dr. David Weinberg, chairman of medicine at Fox Chase Cancer Center in Philadelphia. "They do an even less good job at finding smaller polyps that might be significant."

Weinberg said there's still much to be understood regarding virtual colonoscopy, such as how often patients should undergo one to make sure polyps that are missed don't have a chance to grow to a dangerous size.

As for the idea of laxative-free virtual colonoscopy, he said, "the technique needs to continue to evolve before it's likely to be an important and frequently utilized alternative to colon cancer screening."

The study, funded in part by GE Healthcare, manufacturer of the contrast agent, appears in the May 15 issue of the Annals of Internal Medicine.

More information

For more about colon cancer, visit the U.S. National Library of Medicine.

SOURCES: Michael E. Zalis, M.D., director, CT colonography, department of radiology, Massachusetts General Hospital, and associate professor, radiology, Harvard Medical School, Boston; David Weinberg, M.D., chairman, medicine, Fox Chase Cancer Center, Philadelphia; May 15, 2012, Annals of Internal Medicine

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