Laxative-free virtual colonoscopy can detect large polyps
Computed tomographic (CT) colonography performed on persons who did not undergo laxative-induced bowel cleansing before the screening test accurately detected adenomas 10 mm or larger. However, the test was less accurate for smaller lesions among these patients.
The American Cancer Society has approved CT colonography, or virtual colonography, as a valid screening test for colorectal cancer. Although this method uses a CT scanner to screen for colon cancer and polyps noninvasively, patients are still required to take a bowel-cleansing laxative before the procedure, as is the case for standard optical colonoscopy. The laxative bowel preparation prevents some people from participating in screening, noted Judy Yee, MD, chief of radiology at the San Francisco (California) VA Medical Center and professor and vice chair of radiology at University of California, San Francisco, and coinvestigators in their report for Annals of Internal Medicine (2012;156:692-702). The team sought to assess the performance of laxative-free, CT colonography in detecting adenomas 6 mm or larger, as well as the patient experience.
The prospective test comparison of laxative-free CT colonography and optical colonoscopy involved 605 adults, aged 50 to 85 years, who were at average to moderate risk for colon cancer. The study revealed the following:
- For adenomas 10 mm or larger, per-patient sensitivity and specificity for CT colonography was 91% and 85%, respectively, vs 95% and 89%, respectively, for optical colonoscopy—statistically insignificant differences.
- For adenomas 8 mm or larger, sensitivity of CT colonography was 70%, vs 88% for optical colonoscopy.
- For adenomas 6 mm or larger, sensitivity of CT colonography was 59%, vs 76% for optical colonoscopy.
- Specificity for optical colonoscopy was greater than that for CT colonography for adenomas 8 mm (91% vs 86%) and for adenomas 6 mm or larger (94% vs. 88%).
- Patient's reported more comfort and less difficulty of examination preparation with CT colonography than with optical colonoscopy.
The researchers concluded that these results suggest a possible role for laxative-free CT colonography, which is still in the early stages of development, as an alternative screening method.