CT colonography tattles on false negatives in colonoscopy

Colonoscopy misses or misjudges a substantial percentage of polyps that CT colonography can correctly flag as problematic, a study at the University of Wisconsin suggests.

In a retrospective analysis of more than 9,300 patient cases, researchers found 31 of 144 medium-to-large polyps subjected to discordant-readings review proved out CT colonography’s positive findings over colonoscopy’s negatives.

That’s some 40 percent, and it’s especially striking since the endoscopists had knowledge of the CT colonographic findings going in.

From this and additional data the study’s authors, led by radiology resident B. Dustin Pooler, MD, reported ahead of print in Radiology that discordant polyps—those detected with CT colonography but not confirmed with subsequent colonoscopy—“require secondary review and consideration for follow-up because many ultimately prove to be clinically significant lesions.”

Unsurprisingly, the team found that colonoscopy false negatives were most prevalent in the hard-to-navigate right colon.

Meanwhile, 81 percent of colonoscopy false-negative lesions that were ultimately resected (21 of 26) were adenomas or serrated lesions. Of these, 43 percent (nine of 21) were characterized as advanced lesions, and 89 percent (eight of nine) of advanced lesions occurred in the right colon.

In the study, lesions missed in colonoscopy despite a priori knowledge of their size, location and morphologic structure with CT colonography were, on average, larger than 8 mm in diameter.

They were also more likely to be called “with higher diagnostic confidence with the initial CT colonography examination,” the authors write, adding that their findings should help point the way to improving colorectal cancer-screening strategies.

Read the full study.