[CT-colonography with the 16-slice CT for the diagnostic evaluation of colorectal neoplasms and inflammatory colon diseases].

PURPOSE: Comparison of the performance of virtual and conventional colonoscopy for the detection of colorectal polyps and inflammatory colon diseases using a 16-slice spiral CT scanner. Furthermore, presentation of the first experiences with a new three-dimensional reconstruction mode ("colon-dissection") that dissects the colonic wall like a pathologic-anatomic preparation to increase the sensitivity.

MATERIALS AND METHODS: Forty patients were studied using a 16-slice spiral CT (Lightspeed 16, General Electric Medical Systems, Milwaukee, Wisconsin 53201, USA). The examination was performed after standard oral preparation for colonoscopy. The colonic distension was achieved with room air and intravenous butylscopolamine. Images were obtained in supine and prone position using a detector configuration of 16 x 0.625 mm, pitch 1.7, rotation time 0.5 s, 160 mAs and 120 kV. Axial reconstruction with a slice thickness of 0.625 mm. The CT data were assessed by two radiologists on an Advantage Workstation (Volume Analysis 2, USA) using a software with the capabilities of axial, multiplanar and volume rendering, virtual endoscopy, and colon dissection. Conventional colonoscopy was used to determine the sensitivity.

RESULTS: A total of 30 polyps were found in 8 patients and a carcinoma was detected in two patients. Colonography identified 4 polyps with a diameter of 10 mm or more, 6 polyps with a diameter of 5 mm to 9.9 mm, 11 polyps with a diameter of 3 to 4.9 mm and 9 polyps with a diameter of 3.0 mm or less. There were two false negative findings (one polyp of 3 mm and one of 4 mm had been overseen) and two false positive findings for polyps (polyps of 4 mm and 6 mm). The sensitivity and specificity for the detection of colonic polyps were 93% and 94% with the "colonic-dissection" mode, 87 % and 94 % with the "virtual-endoscopy" mode and 63 % and 97 % with multi-planar reconstruction, respectively. Depending on the diameter of the colonic polyps, the "colon-dissection" mode ("virtual-coloscopy") had a sensitivity and specificity of 100 % and 100 % for polyps with a diameter over 5.0 mm, 91 % and 82 % for polyps with a diameter from 3.0 to 4.9 mm and 89 % and 78 % for polyps with a diameter under 3.0 mm, respectively. Inflammatory colon diseases presented as thickening of the colon wall over 5 mm.

CONCLUSIONS: Virtual colonoscopy with 16-slice spiral CT allows accurate detection of colonic polyps, including small polyps below a diameter of 3 mm. In comparison with the 2D- and 3D-"virtual-endoscopic" reconstruction, the 3D-reconstruction software "colon-dissection" achieves the highest sensitivity for the detection of colonic masses. Therefore, the combination of a 16-slice spiral CT and the "colon-dissection" reconstruction software provides a high resolution in the z-axis for detecting colonic masses and polyps down to a diameter of less than 2 mm, with a sensitivity of about 90 %. This sensitivity is much higher than the sensitivity achievable with 4-slice spiral CT and without "colon-dissection" mode. A thickened colon wall over 5 mm indicates inflammatory colon disease.