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CT colonography detects 90 per cent of colorectal adenomas and cancers measuring 10 mm or more, according to a study conducted by the American College of Radiology Imaging Network.

Computed tomography colonography detects 90 per cent of colorectal adenomas and cancers measuring 10 mm or more, according to a study conducted by the American College of Radiology Imaging Network.

"The National CT Colonography Trial represents the largest study to date of CT colonography, with 2600 patients across the nation at 15 different centers, in both academic and private practices," and thus reflects usual clinical practice, principal investigator Dr. C. Daniel Johnson of the Mayo Clinic in Scottsdale, Arizona, said during an interview with Reuters Health.

The trial results appear in the September 18th issue of the New England Journal of Medicine.

The study participants, age 50 years and older, underwent laxative purgation, stool and fluid tagging, and mechanical colonic insufflation prior to CT colonography performed with multidetector-row CT scanner. Optical colonoscopic examinations were performed the same day, and were used as the reference standard.

For lesions 10 mm in diameter or larger, CT colonography sensitivity was 90 per cent and specificity was 86 per cent; the positive and negative predictive values were 23 per cent and 99 per cent, respectively.

"In 2003, the sensitivity for colonoscopy was determined to be 88 per cent for 1 cm lesions, so the two procedures are comparable for sensitivity," Dr. Johnson noted.

Earlier this year, new policy guidelines for colon cancer screening included CT colonography, he added, "and our data definitely substantiate that decision."

He pointed out that procedural complications are rare with CT colonography, and that the cost is expected to be about half that of colonoscopy. "Plus patients don't need to have someone else drive them to the hospital; there's no IV, no sedation, and patients can go right back to work afterwards," he added.

Moreover, "because there is such high contrast between the air-filled colon lumen and the dense colon wall, a relatively low dose of radiation is needed in order to see polyps protruding into the lumen, so our study was performed with a 50% dose reduction over standard CT examinations," Dr. Johnson noted. "So patients should not be concerned about the very low radiation dose we are using."

N Engl J Med 2008;359:1207-1217