Clinical Role of Three-dimensional Endoscopic Ultrasonography for Estimating the Depth of Early Colorectal Cancer Invasion

Objective: EUS has been established to be useful for estimating the depth of early colorectal cancer (CRC) invasion. With conventional equipment, the ability to image lesions can depend on tumor site or macroscopic type. We examined whether 3-dimensional (3-D) EUS can overcome imaging difficulties associated with conventional EUS.

Methods: We studied 479 lesions of early CRC which underwent EUS. They consisted of 263 lesions of mucosal cancer and 216 lesions of submucosal (sm) cancer. We compared the proportions of difficult-to-image lesions and estimated the depth of invasion between 106 lesions examined by 3-D EUS (3-D EUS group) and 373 lesions by conventional EUS (conventional EUS group). Sm cancers were divided into 2 groups: sm-slight cancers, submucosal invasion depth less than 1mm; and sm-massive cancers, submucosal invasion depth 1mm or greater.

Results: 1) The percentage of difficult-to-image lesions was significantly lower in the 3-D EUS group (1%) than in the conventional EUS group (14%; p<0.001). In the conventional EUS group, difficulty in imaging was caused mainly by poor vertical scans and deep attenuation of the echo. 2) Among lesions able to be evaluated by EUS, the rate of correctly differentiating mucosal and sm-slight cancers (indicated for endoscopic resection) from sm-massive cancers (indicated for radical operation) was 91% in both the 3-D EUS group and the conventional EUS group. However, when difficult-to-image lesions were included, the rate of accurate diagnosis was significantly higher in the 3-D EUS group (90%) than in the conventional EUS group (78%, p=0.004). 3) The depth of invasion could be evaluated only on linear images for 27 lesions (26%) in the 3-D EUS group.

Conclusions: 3-D EUS can overcome the problem of difficult-to-image lesions and improve the accuracy of the estimated depth of early colorectal cancer invasion.