CT colonography with less laxative and no CAD proves an ‘efficient triage exam’

Patients readily accept reduced-laxative CT colonography, and, for those who have had a positive fecal immunochemical test (FIT), the scan is an efficient triage exam when used without computer-aided detection (CAD).

That’s according to a study conducted at multiple centers in Japan and published online Aug. 31 in Radiology.

Kenichi Utano, MD, PhD, of Jichi Medical University and colleagues further found that this imaging option is not so great at detecting neoplasms that are flat, depressed or only slightly raised—that is, non-polypoid—but it’s impressively adept at finding polypoid neoplasms six millimeters or larger.

The researchers recruited 304 FIT-positive patients to undergo both colonoscopy and CT colonography, the latter preceded the previous day by a reduced-laxative method earlier found feasible and useful in a separate study.

The main outcome measures they sought were the accuracy of CT colonography without CAD for finding neoplasms six millimeters or larger in per-patient and per-lesion analyses.

They also surveyed the patients on their experience with the reduced-laxative preparation as well as the exam.

The team found that the per-patient sensitivity, specificity, positive predictive value and negative predictive value of reduced-laxative CT colonography for the detection of neoplasms 10 millimeters or larger were, respectively, 0.91 (40 of 44), 0.99 (255 of 258), 0.93 (40 of 43) and 0.98 (255 of 259).

The measures for neoplasms six millimeters or larger were, per patient and in the same order as above, 0.90 (71 of 79), 0.93 (207 of 223), 0.82 (71 of 87) and 0.96 (207 of 215).

Similarly impressive were per-lesion sensitivities for the detection of polypoid and non-polypoid neoplasms 10 millimeters or larger: 0.95 (40 of 42) and 0.67 (six of nine), respectively.

Sensitivities for neoplasms six millimeters or larger were 0.90 (104 of 115) and 0.38 (eight of 21).

Meanwhile, the authors report, patient acceptance of the preparation for, and exam of, reduced-laxative CT colonography was significantly higher than that for colonoscopy.

Some 62 percent of patients said they would choose CT colonography, while only 10 percent said they would favor colonoscopy, if they had a positive FIT result in the future.

Among the study limitations the authors acknowledge are its relatively small sample and its having only three CT colonography readers, which may have limited the researchers’ ability to understand possible variations in reader performance.

In their discussion, Utano et al. state that, when considering the use of CT colonography as a triage study for patients with a positive FIT, a high negative predictive value and a high acceptance rate by patients are both essential.

“A triage examination is most useful when the number of subsequent unnecessary colonoscopy studies is substantially reduced,” they write. “In addition to showing high negative predictive value, our results suggest that if 100 patients with a positive FIT undergo a CT colonography study, only 14 percent would need to undergo colonoscopy when a cutoff size of 10 mm is used at CT colonography.”

Earlier this year CT colonography got a broad thumbs-up from the U.S. Preventive Services Task force and a qualified thumbs-down, for some types of high-risk polyps, from researchers in the Netherlands.