July 26, 2005 Computed tomographic (CT) colonography, known as virtual colonoscopy, can be used to diagnose significant medical problems in organs outside the colon, according to a new study conducted at the San Francisco VA Medical Center (SFVAMC).
In the study, 45 virtual colonoscopy patients out of 500, or 9 percent, were found to have clinically important extracolonic findings ranging from kidney cancers to abdominal aortic aneurysms. In 35 of the patients, or 7 percent, these conditions had not been previously diagnosed.
"That's a fairly large percentage," observes principal investigator and lead author Judy Yee, MD, chief of radiology at SFVAMC. "Depending on the patient population you look at, this finding suggests that it may be more common to find something significant outside of the colon than in the colon with this technique, because there is more likely to be a problem outside the colon." The study is being published in the August 2005 issue of Radiology.
Virtual colonoscopy uses a CT (computed tomography) scanner, which generates a three-dimensional image from a series of two-dimensional X-rays, to screen for cancers and polyps in the colon. It is much less invasive than more conventional screening techniques such as a colonoscopy, in which a flexible tube with an imaging device on the end is inserted all the way through the colon to the lower end of the small intestine, or a lower gastrointestinal (GI) series, in which X-rays are taken of the colon after it has been filled with barium. Unlike these techniques, virtual colonoscopy is not limited to the colon. It is also much quicker -- less than one minute -- versus 30 minutes to an hour for standard colonoscopy and one to two hours for a lower GI series.
"Essentially, we're performing a CT scan of the entire abdomen and pelvis," says Yee, who is also associate professor and vice-chair of radiology at the University of California, San Francisco (UCSF). "This allows us to look at all the solid organs," including the liver, kidneys, pancreas, spleen, gall bladder, adrenal glands, and bladder, plus the lower part of the lungs. In men, the scan includes the prostate; in women, the uterus and ovaries.
"Typically, these are patients who are not symptomatic for their extracolonic lesion; that's not what brought them in for a CT scan," Yee notes. "And they're often at an earlier stage of disease, and thus more amenable to treatment."
Of the 35 patients with significant new extracolonic findings, 25 underwent follow-up imaging studies; of those, 13 were confirmed as needing surgery or further monitoring, and 12 were determined to have benign lesions. Ten of the 35 did not receive any follow-up.
The average additional cost per patient for following up clinically important extracolonic findings was $28.12. "That's relatively low, considering what was found in the patients," says Yee.
The study was conducted on 500 male patients at SFVAMC who were referred for colonoscopy from February 1998 through September 2002. Their mean age was 62.5 years. Thirty-nine percent presented for routine screening and were classified as being at average risk for colon cancer; 61 percent were referred for screening because of one or more symptoms and were considered at high risk for colon cancer.
Patients were followed for an average of three and a half years after screening -- the longest known follow-up in a study of virtual colonoscopy, according to the researchers. There were no significant differences in outcome between average- and high-risk patients. The study did not specifically address findings in the colon; however, in a 2001 study of 300 patients published in Radiology (219:685-692), Yee found that virtual colonoscopy identified every patient with a clinically significant colon polyp.
For Yee, the results of the current study reinforce the potential appeal of virtual colonoscopy for the general public. "Right now, less than 30 percent of Americans who should be screened for colon cancer -- that is, adults age 50 and above -- actually come in for screening," she notes. "The message here is, go out and get screened for colon cancer. If you have a virtual colonoscopy, we will find clinically significant lesions in the colon and can find significant disease outside of the colon as well."
Co-authors of the study include Naveen N. Kumar, MD, of UCSF; Suchitra Godara, MBBS, of SFVAMC; Janice Casamina, MD, Robert Hom, MD, Gregroy Galdino, MD, and Peter Dell, MD, of UCSF; and Darice Liu, MD, of SFVAMC.
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