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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