An initial experience with screening for colon polyps using spiral CT with and without CT colography (virtual...

Computed tomographic (CT) colography (virtual colonoscopy) is a new imaging method for detection of colon polyps and cancer.

To evaluate the sensitivity of CT colography for polyp detection in a population without symptoms that included persons without colon neoplasia and with radiologists blinded to colonoscopic findings.

Forty-six persons without symptoms underwent spiral CT followed by same-day colonoscopy with subsequent inspection of two-dimensional axial CT images, interactive multiplanar images, and surfaced and volume-rendered images of the colon (three-dimensional CT colography).

Three-dimensional CT colography was superior to two-dimensional axial imaging for detection of colon polyps. Three-dimensional CT colography depicted 1 of 4 (25%) adenomas 2 cm in diameter or larger, 6 of 10 (60%) adenomas 1 to 1.9 cm, 6 of 14 (43%) 6 to 9 mm, and 7 of 65 (11%) 5 mm in diameter or smaller. Three-dimensional CT colography showed a polyp that might have led to colonoscopy in 3 of 4 (75%) patients whose largest adenoma was 2 cm or larger, 5 of 6 (83%) patients with largest adenoma 1 to 1.9 cm, 3 of 7 (43%) patients with largest adenoma 6 to 9 mm, and 4 of 16 patients (25%) with largest adenoma 5 mm or smaller. Large, flat adenomas of the right colon were difficult to identify with three-dimensional CT colography. The specificity of three-dimensional CT colography for patients with adenomas 1 cm in diameter or larger was 89%. Examination of patients with missed adenomas after unblinding indicated that meticulous bowel preparation and adequate distention are critical to accurate interpretation. Perceptual errors were common.

CT colography as performed in this study is not adequate as a colorectal cancer screening test. Several technical factors that appear critical to accurate performance of CT colography are defined.