Virtual colonoscopy performs well in large new study

October 5, 2007

Compared with optical colonoscopy, CT colonography achieves similar outcomes with a fraction of the number of polypectomies, according to a study of more than 6200 patients from the University of Wisconsin Medical School.

Compared with optical colonoscopy, CT colonography achieves similar outcomes with a fraction of the number of polypectomies, according to a study of more than 6200 patients from the University of Wisconsin Medical School.

Dr. Perry Pickhardt, an associate professor of radiology at Wisconsin, and colleagues reported results in The New England Journal of Medicine in October. Their experience supports CTC surveillance for polyps sized 6 to 9 mm, rather than polypectomy, according to the authors.

"The 10-mm threshold for polypectomy at asymptomatic screening would probably capture the vast majority of clinically relevant lesions," the authors said.

The NEJM publication followed on the heels of the release of results

from the American College of Radiology Imaging Network screening trial, which found similar sensitivity and specificity for the two screening techniques. Supporters hope these two large, prominent studies will help virtual colonoscopy take off in mainstream screening.

In the NEJM study, researchers compared the screening techniques for two different groups of about 3100 consecutive asymptomatic, average-risk adults. They assessed detection rates of advanced adenomas, which include polyps ≥10 mm or polyps below that size threshold with high-grade dysplasia or a prominent villous component.

CTC detected 123 advanced adenomas (in 3.2% of patients), including 14 cancers. Optical colonoscopy yielded 121 advanced adenomas (3.4% of patients), including four invasive cancers.

Unlike the ACRIN trial, in which both 2D and 3D techniques were used on a randomized basis to make the primary interpretation, researchers in the NEJM study used 3D techniques for primary reads. The CTC protocol included use of cathartic agents (typically 45 mL dose of sodium phosphate), fluid and stool tagging, and mechanical distention with carbon dioxide.

Polyps were placed in three categories: diminutive (≤5 mm), small (6 to 9 mm), or large (≥10 mm). In the CTC group, polyps 10 mm or larger were removed during subsequent therapeutic optical colonoscopy, but patients with polyps sized 6 to 9 mm were given the option of CTC surveillance.

The optical colonoscopy screening protocol called for removal of all polyps, including diminutive findings. Consequently, the number of polypectomies was much larger in the optical colonoscopy group compared with the CTC group (2434 versus 561).

In each screening group, 103 advanced adenomas ≥10 mm were detected. Optical colonoscopy yielded 11 advanced adenomas sized 6 to 9 mm, while CTC picked up five. The figure is lower due to the CTC surveillance approach. Researchers expected there were several small advanced adenomas yet to be found in the surveillance group.

In the CTC group, only 7.9% were referred on for therapeutic optical colonoscopy, similar to the results of the ACRIN colon screening trial. Most patients with polyps in the 6 to 9-mm size range opted for surveillance, and in those already followed up, 96% of polyps were stable or smaller since the original screen. The remaining polyps were removed.

In the two groups combined, there were 20 advanced adenomas under 10 mm. High-grade dysplasia and invasive carcinoma are rare in polyps under this size threshold, the researchers said.

Of 2006 polypectomies performed for diminutive polyps during optical colonoscopy, only four turned up advanced adenomas.

"Such observations reinforce the scarcity of diminutive and small advanced neoplastic lesions and the potential benefits of filtering strategies during CTC," the authors said.

CTC's risk profile was also better, with no complications during screening or therapeutic optical colonoscopy versus seven cases of bowel perforation in the optical colonoscopy group, according to the study.

For more information from the Diagnostic Imaging archives

CT colonography bests conventional imaging in cost-effectiveness test

Positive results strengthen case for CT colonography screening

Virtual colonography proves to be effective, wins reimbursement

CT colonography tools advance in clinical use