3-D virtual colonoscopy more sensitive than conventional procedure

July 1, 1993

n UW Hospital to offer non-invasive screening in early 2004

MADISON—A new technology aimed at the second-deadliest cancer in the nation is both more sensitive and less invasive than the conventional screening method.

If colon cancer is caught in the early stages, it’s 90 percent curable. Until now, conventional colonoscopy has been the standard mode of screening for colon cancer, but because of the uncomfortable nature of the procedure, many individuals opt to not have one done at all—but this may soon change.

Three-dimensional computed tomography (CT) colonography, also known as virtual colonoscopy, is more sensitive and less invasive than conventional colonoscopy in screening average-risk patients, according to research. An article was published in the Dec. 1 issue of the New England Journal of Medicine, and also is featured on their Web site. The new technology allows radiologists to obtain 3-D images from different angles, providing a “movie” of the interior of the colon without having to insert a scope.

“The findings of this study should establish virtual colonoscopy as a viable screening option,” said Perry J. Pickhardt, M.D., associate professor of radiology at University of Wisconsin Medical School, radiologist at UW Hospital and Clinics and lead author of the study from National Naval Medical Center in Bethesda, Md.

Colonic polyps are benign growths that may develop into colon cancer if not removed. Many people resist screening because of the discomfort caused by conventional colonoscopy and other tests. In recent years, radiologists have begun using CT colonography to screen for polyps.

Although less invasive, until now the procedure primarily used 2-D CT slices (images) for polyp detection, which are likely less sensitive.

With the addition of 3-D “fly-through” images, virtual colonoscopy sees the whole picture, providing precise and detailed images of the colon’s interior in a minimally invasive manner.

With virtual colonoscopy, there is no risk of bleeding or of perforating the colon. There is no need for intravenous sedation, and the procedure is less costly than conventional colonoscopy. It also is more convenient, taking 15 minutes or less, because patients need not recover from sedation.

“Three-D Virtual colonoscopy results in a win for patients,” said Pat Turski, MD, chairman of radiology, UW Hospital and Clinics. “Dr. Pickhardt’s findings not only make it possible for us to offer a much more pleasant, non-invasive screening to patients, the efficiency of the technology makes the screening process much more streamlined. Ultimately, we’ll be able to screen more patients, detect colon cancer with more accuracy, resulting in many more lives saved.”

For this study, Dr. Pickhardt and colleagues performed both conventional and virtual colonoscopy on the same day on 1,233 asymptomatic adults, 97.4 percent of whom were at average risk of having colonic polyps. Overall, virtual colonoscopy detected more than 90 percent of significant polyps. For example, virtual colonoscopy detected 92.6 percent of polyps eight mm. and greater, whereas conventional colonoscopy detected 89.5 percent of such polyps.

Two malignant polyps were present, and virtual colonoscopy detected both of them, while conventional colonoscopy missed one.

“This minimally invasive total colonic examination compares favorably with conventional colonoscopy for detection of clinically relevant lesions,” Dr. Pickhardt said.

Most polyps that are missed at virtual colonoscopy are small (5 mm or less) and are of little or no clinical importance, according to Dr. Pickhardt. Virtual colonoscopy is able to identify occasional polyps that are located behind folds in the colon lining and may be missed by conventional colonoscopy. Virtual colonoscopy is strictly a diagnostic procedure and is best suited for average-risk individuals 50 to 70 years of age.

“I believe virtual colonoscopy will eventually join conventional colonoscopy as a major component of colorectal cancer screening in the U.S.,” Dr. Pickhardt said. “This less invasive screening option will likely encourage more adults to seek testing, resulting in many additional lives saved.”

Turski is projecting that UW Hospital and Clinics will be one of the few hospitals in the state to offer the 3-D Virtual Colonoscopy in early 2004.

Radiological Society of North America (RSNA) is an association of more than 33,000 radiologists, radiation oncologists and related scientists committed to promoting excellence through education and by fostering research, with the ultimate goal of improving patient care. The Society is based in Oak Brook, Ill.

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