Colonoscopy Bests CT Scans and X-rays

Detects almost twice as many polyps as other procedures

THURSDAY, Dec. 16, 2004 (HealthDayNews) -- When it comes to detecting precancerous polyps in the colon, no test available today beats the colonoscopy.

That's the conclusion of a new study whose results were so clear that the trial was stopped early. The findings will also be published online before they appear in print in the Jan. 1 issue of The Lancet.

The study found that colonoscopy far outperformed "virtual" colonoscopy using CT scanning, as well as barium enema X-rays, for detecting polyps of various sizes in the colon.

"As these tests are currently performed, the most accurate test is colonoscopy," concluded Dr. Don Rockey, a gastroenterologist at Duke University Medical Center.

Colonoscopy is a procedure that can detect and also treat polyps in the colon. It's is used as a screening tool for colon cancer. A thin, flexible tube is inserted into the rectum and then threaded through the colon. A tiny camera and light let the physician view the colon; if any abnormalities are detected, they can be removed.

By contrast, virtual colonoscopy uses computerized tomography scanning to capture numerous images of the colon and create three-dimensional pictures. This procedure is noninvasive and doesn't require the colon to be distended with air.

In air contrast barium enema (ACBE), the colon is distended with air and barium, a high-density liquid, coats the colon walls. Then X-rays are taken, and the barium acts as a contrast agent so physicians can see any abnormalities. ACBE is the oldest of the three procedures.

All three tests require a day of preparation, including eating a clear liquid diet and cleansing the colon, usually with laxatives or enemas.

From 2001 through 2003, Rockey and his colleagues from medical centers across the United States enrolled 614 people to compare the three different methods. Seventy percent were male. Seventy percent were white, 24 percent were black and 6 percent were of another race. The average age was 57.

All of the study participants had a higher than average risk of developing colon cancer. Some had evidence of blood in their stool, others had a family history of colon cancer, and some had iron-deficiency anemia.

Each person had all three tests. They began with the ACBE. Seven-to-14 days later, they had a virtual colonoscopy, followed on the same day by a standard colonoscopy. The radiologists didn't know which test produced the results they were viewing.

The largest difference was found in the smallest lesions. For polyps that were between 6 millimeters and 9 millimeters, ACBE found 35 percent of the lesions, virtual colonoscopy detected 51 percent, and colonoscopy found 99 percent.

There was also a significant difference for larger polyps. For those over 10 millimeters, colonoscopy was 98 percent accurate, compared to 59 percent for the virtual scan and 48 percent for ACBE. In larger polyps that were considered precancerous, colonoscopy detected 98 percent versus 64 percent for virtual colonoscopy and 55 percent for ACBE.

The highest rates of false positive findings occurred with ACBE.

Rockey acknowledged the technology for CT scanning is advancing rapidly and said the results for virtual scanning might be improved if the study was started today.

"This study kind of reinforces the results of other studies," said Dr. David Beck, chairman of colon and rectal surgery at the Ochsner Clinic Foundation Hospital in New Orleans. He added that it also shows virtual scans won't reduce the number of colonoscopies done any time soon.

Beck said there are patients for whom virtual scans are the test of choice. He said people on anticoagulant medications and those with certain types of diverticulitis are good candidates for virtual scanning.

Both Rockey and Beck said that, along with trying to increase the sensitivity of virtual scans, researchers are also working on ways to perform these tests without having to require the intensive preparation. The preparation, said both Beck and Rockey, is what people really don't like about these tests.

The most important thing people need to know is the importance of getting screened, said Beck. "Colon cancer is preventable and we're working hard on ways to identify it early."

Rockey added, "Everyone over 50 needs to have a colon exam."

More information

To learn more about colonoscopy, go to the National Institute of Diabetes and Digestive and Kidney Disorders.

SOURCES: Don Rockey, M.D., gastroenterologist and professor, medicine, Duke University Medical Center, Durham, N.C.; David Beck, M.D., chairman, colon and rectal surgery, Ochsner Clinic Foundation Hospital, New Orleans; Jan. 1, 2004, The Lancet
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