Nonadenomatous polyps at CT colonography: prevalence, size distribution, and detection rates

Purpose: To prospectively investigate with computed tomographic (CT) colonography the prevalence and size distribution of nonadenomatous polyps in asymptomatic adults and to compare the detection rates of adenomatous and nonadenomatous polyps.

Materials and methods: A total of 1233 asymptomatic adults (mean age, 57.8 years; 505 women, 728 men) underwent same-day CT colonography and optical colonoscopy procedures. CT colonoscopy studies were interpreted prospectively with a primary three-dimensional approach immediately before optical colonoscopy. Statistical analysis was performed with the chi(2) test. Size, prevalence, and by-polyp detection differences were compared between adenomatous and nonadenomatous polyps.

Results: Seven hundred fifty-six (57.7%) colorectal polyps identified at optical colonoscopy in 410 (33.3%) patients were nonadenomatous; of these lesions, 622 (82.3%) were diminutive (</=5 mm). Nonadenomatous polyps accounted for 622 (64.4%) of 966 diminutive lesions and 134 (39.9%) of 344 polyps 6 mm or larger (P <.001). The prevalence rate for nonadenomatous polyps was 8.8% (109 of 1233 patients) and 2.0% (25 of 1233 patients) at 6- and 10-mm thresholds, respectively. CT colonography by-polyp sensitivity for nonadenomatous lesions was 73.1% (98 of 134 patients) and 73.3% (22 of 30 patients) at 6- and 10-mm thresholds, respectively, compared with 85.7% (180 of 210 patients) and 92.2% (47 of 51 patients) for adenomas (P <.01). In 1065 patients that did not have a 6-mm or larger adenoma at optical colonoscopy, CT colonography depicted a nonadenomatous polyp that was 6 mm or larger in 63 (5.9%) patients and a nonadenomatous polyp that was 10 mm or larger in 15 (1.4%) patients.

Conclusion: More than 80% of nonadenomatous polyps were diminutive, but they accounted for nearly 40% of polyps that were 6 mm or larger. Fortunately, CT colonography is significantly (P <.01) less sensitive in the detection of lesions that have no malignant potential when compared with similar-sized adenomas that have malignant potential.