Purpose: To investigate the usefulness of quantitative evaluation of a width of lateral contour on a lateral split-view computed tomographic air-contrast enema (CT enema) image for diagnosing the invasion depth of colorectal cancer (CRC) located on a colorectal fold. Methods: The cases of 22 patients with 22 fold-located CRCs (12 early CRCs and 10 advanced CRCs) who underwent a pretherapeutic computed tomographic colonography were retrospectively examined. T1-stage CRCs were classified into two categories according to the Japanese guideline: T1a-stage, carcinoma invading the superficial submucosa (< 1000 um); and T1b-stage, carcinoma invading the deeper submucosa (≥ 1000 um). The maximum width of a lateral contour of the colorectal fold on which the CRC was located, i.e., the gap distance between the two adjacent haustrations, was calculated from the lateral split-view CT enema image by two gastrointestinal radiologists. These values were compared between the intramucosal / T1a CRCs and the T1b / more deeply invading CRCs. The inter-rater intraclass correlation coefficients were also evaluated for reliability. Results: The maximum widths of a lateral contour of the colorectal fold were significantly higher in the T1b / more deeply invading CRCs than in the intramucosal / T1a CRCs (p<0.0001). The optimum cut-off value of the maximum width of a lateral contour of the colorectal fold for differentiating the former from the latter was 6.0 mm, with a sensitivity and specificity of 100% and 100%, respectively. The inter-rater intraclass correlation coefficient for measurement of a lateral contour of the colorectal fold was 0.958. Conclusions: We demonstrated for the first time that quantitative evaluation of a width of lateral contour using a lateral split-view CT enema image can improve the diagnostic accuracy of the invasion depth for CRCs located on a colorectal fold.

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