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Repeat CT Colonography Detects Fewer Large Polyps


Repeat CT colonography may help detect more advanced right-sided lesions, but they detect fewer large polyps.

Fewer large polyps are detected with repeat CT colonography screening, although more advanced right-sided lesions are found, according to a study published in Radiology.

Researchers from the University of Wisconsin School of Medicine and Public Health in Madison sought to determine the rate and types of polyps detected at repeat CT colonography screening after initial negative findings at CT colonography screening.

The study included 5,640 patients with negative CT colonography screenings (no polyps ≥ 6 mm) performed before 2010 at one medical center. A total of 1,429 (25.3%; 736 women, 693 men) returned for repeat screenings. Their mean age was 61.4, mean interval between screenings was 5.7 years. The researchers compared the positive and histologic findings of initial and repeat screenings. For all patients with positive findings at repeat CT colonography, the findings were directly compared with the initial CT colonography findings.

The results showed that repeat CT colonography screenings were positive for lesions 6 mm or larger in 173 (12.1%) adults (compared with 14.3% at initial CT colonography screening). In the 173 patients, 29.5% (61 of 207) of nondiminutive polyps could be identified as diminutive at the initial CT colonography and 12.6% (26 of 207) were missed.

Other findings included:

Detected at Follow-up CT
Detected at Initial CT
Large polyps
3.8% (55 of 1,429)
Advanced neoplasia (advanced adenomas and cancer)
2.8% (40 of 1,429)
Invasive cancer
0.14% (2 of 1,429)


The researchers concluded that positive rates for large polyps at repeat CT colonography screening were lower compared with those at initial screening, but more advanced right-sided lesions were detected at follow-up CT colonography, many of which were flat, serrated lesions. “The cumulative findings support both the nonreporting of diminutive lesions and a 5–10-year screening interval,” they wrote.

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