Computed tomographic (CT) colonography has been compared previously with colonoscopy, but has mainly been assessed in patients with positive screening test results or symptoms.
For this reason, the data that is currently available may not apply to screening of patients with a personal or family history of colorectal polyps, or an increased risk of cancer.
It was with this background in mind that Dutch researchers have investigated the ability of CT colonography to identify individuals with large (10 mm) colorectal polyps inconsecutive patients at increased risk for colorectal cancer.
The researchers prospectively investigated 249 consecutive patients, who all underwent CT colonography prior to colonoscopy.
CT colonography examinations were interpreted independently by two reviewers, with sensitivity, specificity, and predictive values determined after careful matching of CT colonography with colonoscopy.
|The high proportion of missed flat lesions requires more study.|
In the instance of unexplained large false-positive findings a second-look colonoscopy was carried out for verification.
Thirty-one patients (12%) were found to have large polyps at colonoscopy, with a total of 48 polyps being discovered.
This included 8 patients with 8 large polyps that were overlooked initially and only detected at the second-look colonoscopy.
In 6 of these 8 patients, the over-looked polyp was the only large lesion.
With CT colonography, 84% of patients, (26 of 31) who had large polyps were correctly identified, paired for a specificity of 92% (200 – 201.218).
Positive and negative predictive values were 59% – 60% (26/43 – 44) and 98% (200 – 201/205 – 206), respectively.
CT colonography detected 75%–77% (36–37/48) of large polyps, with 9 of the missed lesions being flat.
The findings of the study show that CT colonography and colonoscopy have a similar ability to identify individuals with large polyps in patients at increased risk for colorectal cancer, say the study authors.
They add that the high proportion of missed flat lesions warrants further study.