Comparative study of three-dimensional and conventional endorectal ultrasonography used in rectal cancer staging

Three-dimensional (3D) imaging offers improved knowledge of various anatomic structures and tumors by providing 3D images. This prospective study was performed to verify whether 3D endorectal ultrasonography (EUS) enhances the accuracy of rectal cancer staging, as compared with conventional EUS.

Using both 3D and conventional EUS, 33 consecutive patients with operable rectal cancer were preoperatively staged. A rigid 3D probe with a scanner was used for 3D EUS, and a rigid endorectal probe with a scanner was used for conventional EUS.

The accuracy of 3D EUS was 90.9% for pT2 and 84.8% for pT3, whereas that of conventional EUS was 84.8% and 75.8%, respectively, thereby showing no difference between these two methods. The lymph node metastasis was accurately predicted by 3D EUS in 28 patients (84.8%), whereas conventional EUS predicted the disorder in 22 patients (66.7%). The difference was not statistically significant. The average infiltration grade of the circumference on transverse 3D EUS scans was associated closely with advancement of the TNM stage (p <0.001-0.006) and lymph node metastasis (p = 0.003). The presence of a cone-shaped surface on the deep tumor border correlated with the infiltration grade shown on all of the sectional displays (p <0.001-0.042) and with advancement of the TNM stage (p = 0.018).

Although the findings did not show 3D EUS to have a significant advantage over conventional EUS for the accurate evaluation of rectal cancer, a numeric advantage may possibly be statistically significant in a further study with larger cases. Furthermore, stereoscopic visualization provided easier and complete understanding of both focal lesions and lymph nodes.