Correlation Between Endorectal Ultrasound and Magnetic Resonance Imaging for Predicting the Circumferential Resection Margin in Patients With Mid‐Low Rectal Cancer Without Preoperative Chemoradiotherapy

Objectives To assess the correlation between endorectal ultrasound (ERUS) and magnetic resonance imaging (MRI) in predicting the circumferential resection margin (CRM) status of patients with mid‐low rectal cancer without preoperative chemoradiotherapy. Methods Twenty patients with rectal cancer who did not receive preoperative chemoradiotherapy and underwent ERUS and MRI examinations before total mesorectal excision from May 2018 to April 2019 were included in this study. The patient and tumor characteristics, lymph nodes, tumor stages, ERUS and MRI predictors of the CRM status, and postoperative pathologic results were recorded. The closest distance between the deepest portion of lesion invasion and the mesorectal fascia was independently measured on MRI and ERUS images by 2 observers. The observers were blinded to the pathologic results. Measurements from ERUS and MRI were compared. Results The mean distance between the distal edge of the lesion and the anal verge was 5.7 cm (range, 3.1–8.1 cm). The ERUS and pathologic evaluations of CRM involvement were consistent in 90% of the cases. The MRI and pathologic evaluations of CRM involvement were concordant in 95% of the cases. The Cohen κ coefficient of ERUS and MRI was 0.608 (P = .007). The correlation coefficient of ERUS and MRI for assessing the closest distance from the edge of cancer invasion to the mesorectal fascia was 0.99 (P = .0005). Conclusions Endorectal ultrasound and MRI assessments of the preoperative CRM status appear to be highly consistent. Endorectal ultrasound can be used as a complementary tool with MRI to predict the CRM status of patients with mid‐low rectal cancer without preoperative chemoradiotherapy.