Virtual colonoscopy still not ready for widespread use

Although improvements have been made to virtual colonoscopy in recent years, findings from two studies in the August issue of Gastroenterology suggest that it is still not ready to be used as a widespread screening test for colon cancer.

“If you look at all of the literature on it, we’re just not there yet,” Dr. Douglas K. Rex, author of a related editorial, told Reuters Health. “There’s no question that we need tests that are more appealing to patients” than standard colonoscopy, Dr. Rex, from Indiana University Hospital in Indianapolis, noted. “But right now, we just don’t have a good sense of the cost-effectiveness of virtual colonoscopy,” he added. In one study, Dr. Benoit C. Pineau and colleagues, from Wake Forest University in Winston-Salem, North Carolina, compared virtual colonoscopy plus oral contrast with standard colonoscopy in 205 patients. Overall, virtual colonoscopy was 61.8% sensitive and 70.7% specific in identifying patients with colorectal lesions, the researchers state. As expected, with higher lesion sizes, the accuracy improved. For example, virtual colonoscopy was 90% sensitive and 94.6% specific in identifying patients with lesions 10 mm or greater in size.Virtual colonoscopy was associated with a negative predictive value of 98.9% when the 10-mm cutoff size was used. Using this cutoff, the test could preclude the need for standard colonoscopy in 86% of patients with a false-negative rate of 1%.Despite these encouraging findings, the authors note that “further studies are needed to determine what lesion cutoff size is clinically acceptable and the appropriate interval time for repeat virtual colonoscopy when it detects lesions below this cutoff size.” In the other study, Dr. C. Daniel Johnson and colleagues, from the Mayo Clinic in Rochester, Minnesota, evaluated virtual colonoscopy as a screening test for polyps in 703 subjects. As in the first study, all of the patients were tested with standard colonoscopy later the same day.”This study is really the first to feature a group with a low prevalence of polyps similar to that seen in the general population,” Dr. Rex pointed out.Whether polyps were detected with virtual colonoscopy depended largely on who was reading the image and the lesion size. For example, compared with the standard colonoscopy results, one reader detected 73% of polyps 1 cm or greater in diameter, while another only detected 32% of such polyps. For smaller polyps, the corresponding detection rates for these readers were 57% and 29%.As in the first study, virtual colonoscopy had a fairly high specificity, which increased further as lesion sizes rose, Dr. Johnson’s team notes.The accuracy of virtual colonoscopy reported in studies featuring selected patient groups may overestimate its performance in a screening setting, the authors state. Technologic refinements should be explored to enhance detection rates in low prevalence cohorts. (Source: Gastroenterology 2003;125:304-319,608-614: Reuters Health: Anthony J. Brown, MD: September 5, 2003: Oncolink)