Laxative-Free Colonography Procedure Effective in Detecting Larger Polyps

Many people choose to avoid participation in colon screening as the OC and CTC procedures in use require strong laxative preparation. Also, OC (though not CTC) requires sedation. Researchers based mainly at Massachusetts General Hospital (MGH; Boston, MA, USA) have developed an innovative laxative-free CTC (LF-CTC) protocol that involves “electronic cleansing” followed by computer-aided polyp detection.

Preparation for this virtual colonoscopy involves two days of a low-fiber diet and oral ingestion of small doses of a contrast agent to label fecal material in the colon. Software programs developed by the MGH Imaging team subtract labeled feces from the acquired CT images then analyze them for the presence of lesions – primarily adenomas, the type most likely to develop into cancer.

The study assessed LF-CTC performance in detecting adenomatous polyps 6 mm or larger in asymptomatic adults aged 50 to 85 years, at average to moderate risk for colon cancer. Patients already scheduled for screening colonoscopy were recruited from four US hospitals; 604 patients completed the full protocol. The LF-CTCs were performed within 5 weeks before the scheduled OCs. Gastroenterologists performing the OCs were not informed of polyps identified in the LF-OTCs until they had completed the initial examination, allowing a second-pass colonoscopy to confirm and if necessary remove any missed polyps.

In this initial clinical trial, reported May 15, 2012, in the journal Annals of Internal Medicine, the new technique identified more than 90 percent of adenoma type polyps that were 10 mm or larger. Among colonoscopy-confirmed lesions that showed higher-risk associated changes, 85 percent were 10 mm or larger. Three cases of colon cancer were diagnosed, all of which were 10 mm or larger and were detected by both screening methods.

"Colon cancer [...] is largely preventable through screening. So the most important thing is for all adults over 50 to be screened," said Michael Zalis, MD, director of CT Colonography at MGH Imaging, who led the study. “If these results hold up in larger trials, we would expect this procedure would first be offered to moderate-risk patients who are otherwise unable or unwilling to be screened," he added; "If we can validate that this form of CT colonography performs reasonably well [...], it could have a significant impact on reducing the incidence of colon cancer and related cancer deaths."

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