CT Colonography

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CT identifies large polyps during colorectal screening

Last Updated: July 29, 2004

NEW YORK (Reuters Health) - CT colonography is similar to colonoscopy

in its ability to identify large polyps in patients at increased risk

for colorectal cancer, researchers report in the July issue of

Gastroenterology.

Colonoscopy is the investigation of choice for patients with personal

or family history of colorectal polyps or cancer, the authors

explain, but the discomfort caused by the procedure often leads

patients to decline screening.

Dr. Rogier E. van Gelder from Academic Medical Center of the

University of Amsterdam and colleagues assessed the ability of CT

colonography to identify patients with polyps at least 10 mm in size

and performed a second-look colonoscopy to verify large, unexplained

false-positive findings.

Colonoscopy required a median of 30 minutes, the report indicates,

compared with 21 minutes examination room time and 14 minutes

evaluation time for CT colonography.

CT colonography identified 84% of patients with at least 1 large

polyp, the authors report, and the mean specificity for identifying

patients without large polyps was 92%.

Sensitivity was much lower for flat polyps than for sessile or

pedunculated polyps, the results indicate.

Because of a large number of false-positive findings, due mainly to

residual stool in the colon, the mean positive predictive value of CT

colonography was only 61% for large polyps and 17% for medium-sized

polyps. Negative predictive values were better, the researchers note,

at 98% and 94%, respectively, for large and medium-sized polyps.

" CT colonography has potential to become a colorectal cancer

screening option as its accuracy for patients with large lesions is

similar to colonoscopy, " Dr. van Gelder told Reuters Health.

" However, as yet several problems remain to be solved, such as the

poor detection of flat lesions and the high number of false positive

findings, " Dr. van Gelder said. " If future research can

satisfactorily answer those questions, CT colonography becomes a

realistic screening option. "

" At present we are investigating the use of alternative bowel

preparation for CT colonography to find out its effect on patient

acceptance and accuracy, " Dr. van Gelder added. " We are also

investigating several computer algorithms to improve the accuracy of

CT colonography. "

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This online resource is supported by: Sanofi-Synthelabo

www.asco.org c Copyright 2002 American Society of Clinical Oncology

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