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DOI:10.2214/AJR.07.2076
AJR 2007; 189:35-40
© American Roentgen Ray Society

Original Research

Colorectal Polyps on Portal Phase Contrast-Enhanced CT Colonography: Lesion Attenuation and Distinction from Tagged Feces

Seung Soo Lee1, Seong Ho Park1, Eugene K. Choi2, So Yeon Kim1, Min-Ju Kim1, Kyoung Ho Lee3 and Young Hoon Kim3

1 Department of Radiology and Research Institute of Radiology, University of Ulsan College of Medicine, Asan Medical Center, 388-1 Poongnap2-Dong, Songpa-Gu, Seoul 138-040, Korea.
2 Weill Medical College of Cornell University, New York, NY.
3 Department of Radiology, Seoul National University College of Medicine, Seoul National University Bundang Hospital, Seongnam-si, Korea.

OBJECTIVE. The purpose of our study was to determine the attenuation of colorectal polyps on portal phase contrast-enhanced CT colonography (CTC) and evaluate whether enhanced polyps can be clearly distinguished from tagged feces during CTC review.

MATERIALS AND METHODS. Our institutional review board approved this study and waived patient informed consent. Forty-eight colonoscopy-proven polyps (6–20 mm) and 41 polypoid tagged feces (6–19 mm) were selected from contrast-enhanced CTC performed without (n = 37 examinations) and with (n = 10 examinations) fecal tagging, respectively. Scanning was performed 72 seconds after IV injection of 150 mL of contrast material at a rate of 2.5 mL/s. Fecal tagging consisted of three doses of 200 mL of 5% weight/volume (w/v) barium sulfate suspension taken at each meal the day before CTC. Attenuation of the polyps and tagged feces was measured. Four independent blinded radiologists reviewed the polyps and tagged feces at both wide (width, 1,500 H; level –400 H) and soft-tissue (width, 400 H; level, 20 H) window settings to distinguish them by using subjective visual assessment.

RESULTS. Polyp attenuation on the portal phase was not correlated with size (R = –0.003; p = 0.99) and was not different between histologic types (p = 0.884). Enhanced polyps (mean ± SD, 119.9 ± 25.3 H; range, 50–173 H) showed significantly lower attenuation than did tagged feces (1,521.4 ± 683.6 H; range, 495–2,683 H) without any overlap (p < 0.0005). An 8-mm sessile adenomatous polyp was misinterpreted as tagged feces by one reviewer. The rest of the lesions were correctly interpreted by all reviewers, resulting in high interobserver agreement (kappa value, 0.988).

CONCLUSION. Polyp attenuation on portal phase contrast-enhanced CTC ranges from 50 to 173 H. Contrast-enhanced polyps are clearly and consistently distinguished from barium-tagged polypoid feces.

Keywords: attenuation • colorectal polyps • CT colonography • fecal tagging


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