UW Researcher Leads Groundbreaking Study of Colonscopy Miss Rates

UW Health Services

3-D Virtual Colonoscopy

Perry Pickhardt, MD
MADISON - Conventional colonoscopy has been considered the gold standard of screening for colon cancer for years, but its effectiveness in detecting polyps (the protruding growths that can become cancerous) has been compared only against itself, until now.
For the first time, researchers have now evaluated both screening tools on the same population and found that conventional colonoscopy missed 12 percent of the largest polyps.
That "miss rate" is double that of previous studies in which conventional colonoscopy was used as its own reference standard.
The study, to be published in the Annals of Internal Medicine September 7, 2004, involved 1,233 asymptomatic adults who each underwent same-day virtual and conventional (also known as optical) colonoscopies as part of a multi-center screening trial. When 3-D Virtual Colonoscopy was used as the reference standard, results showed that the conventional colonoscopy miss rate for polyps at the 10 millimeter threshold was 11.8 percent.
"Optical colonoscopy has been widely accepted as the gold standard for detection of colorectal neoplasia," states Perry Pickhardt, MD (pictured, above left), associate professor of radiology at the University of Wisconsin Medical School, radiologist at UW Hospital and Clinics, and lead author of the study. "It continues to be a wonderful study, but it is far from perfect."
Improving Upon Previous Studies
Dr. Pickhardt says a notable weakness common to all previous studies was that optical colonoscopy was used as its own reference standard. This means that if a polyp is initially missed at optical colonoscopy primarily because of its location (such as behind a fold) and not because of perceptual error, it's more likely to be missed at subsequent optical colonoscopy evaluation, unless the viewer is specifically directed to that location.
"To our knowledge, this is the first study to directly investigate the adenoma (polyp) miss rate at optical colonoscopy using a separate standard for comparison," states Pickhardt.
"Using virtual colonoscopy as the reference standard resulted in a higher miss rate with optical colonoscopy, mainly on the larger, higher-risk polyps that are more likely to develop into cancer," Pickhardt adds. "The data provides not only novel insight into optical colonoscopy miss rates, but also indicates the relative blind spots where more attention could be focused."
Three-dimensional virtual 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. 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.
Conventional colonoscopy involves a visual exam of the lining of the colon with a colonoscope, a flexible tube containing a light and viewing device. It allows the physician to view the inside of the colon through a video camera while the patient is heavily sedated.
Virtual colonoscopy is able to identify occasional polyps that are located behind folds in the colon lining and may be missed by conventional colonoscopy. Most polyps missed with virtual colonoscopy are small (5 mm or less) and are of little or no clinical importance, according to Dr. Pickhardt.
Pairing Screening Methods
Many people resist screening because of the discomfort of conventional colonoscopy and other tests. If colon cancer is caught in the early stages, it's 90 percent curable. Dr. Pickhardt says by allowing patients and physicians to choose between conventional or virtual colonoscopy, more individuals may get screened, thereby catching colon cancer in its treatable phases and preventing more deaths.
"I believe that virtual and conventional colonoscopy will soon comprise the two major components of colorectal cancer screening in the U.S.," Dr. Pickhardt said. "But with any medical procedure used to screen individuals for cancer, medical professionals want to know they're using the most effective method in order to save lives."
"By conducting this study, we discovered conventional colonoscopy is still a reliable test, but one that should not be solely relied upon," Pickhardt adds. "The effectiveness of virtual colonoscopy paired with conventional cannot be overlooked, especially when you consider that they have a combined sensitivity of 100 percent in detecting colon cancer and significant precancerous polyps."
Dr. Pickhardt co-authored the Adenoma Miss Rate study with four other physicians from the National Naval Medical Center, Bethesda, MD; the Naval Medical Center San Diego, San Diego, CA; the Uniformed Services University of the Health Sciences, Bethesda, MD; and the Division of Cancer Prevention, National Cancer Institute, Bethesda, MD. Dr. Pickhardt was also the lead author on the first 3-D virtual colonoscopy study published in the New England Journal of Medicine in December, 2003.

Date Published: 06/06/2007

News tag(s):  digestive health

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