Diagnosis of early colorectal cancer invasion depth by quantitative evaluation of the basal indentation in CT colonography

Objective: To investigate the feasibility of diagnosing the invasion depth of early colorectal cancer (CRC) by quantitatively evaluating the basal indentation (BI)—i.e., the intestinal lateral deformity—in CT colonography (CTC). Materials and methods: 34 early CRCs (13 Tis CRCs and 21 T1 CRCs) in 32 patients who underwent a preoperative CTC were retrospectively examined. Two radiologists calculated the depth of the BI on a computed tomographic air-contrast enema (CT enema) image, the depth of the BI due to the geometric function (BI-G) on a cross-sectional multiplanar reconstruction (CS-MPR) image, and the ratio of the BI to the BI-G (i.e., the “BI ratio”) for each lesion. The BI ratios of the Tis and T1 CRCs were compared. Results: The BI ratios were significantly higher in the T1 CRCs than in the Tis CRCs (p < 0.0001). The optimum cutoff value of the BI ratio for differentiating the T1 CRCs from the Tis CRCs was 1.64, with a sensitivity, specificity, and area under the curve of 90.5 %, 100 %, and 0.974, respectively. Conclusions: We have demonstrated for the first time that quantitatively evaluating the BI can improve the accuracy of diagnosis of early CRC invasion depth.