Objective  To evaluate the feasibility and accuracy of endorectal ultrasound (ERUS) in predicting the circumferential resection margin (CRM) of rectal cancer.

  Methods  Between May 2010 and December 2013, 120 patients with rectal cancer preoperatively evaluated with ERUS in Peking Union Medical College Hospital were retrospectively analyzed. The patients underwent total mesorectal excision without neoadjuvant chemoradiotherapy. CRM was measured with preoperative ERUS, i.e. the shortest distance between the outer edge of tumor and the mesorectal fascia. With pathological results as gold standard, the diagnostic values of ERUS under different criteria for CRM were assessed. The diagnostic accuracies of ERUS in predicting CRM among different positions, distances from the anal verge, and stages were analyzed.

  Results  ERUS showed mesorectal fascia in 114 cases (95%). The display rates of mesorectal fascia by ERUS with different transducer frequencies were significantly different (P=0.034). With CRM ≤ 2 mm as the standard, the sensitivity, accuracy and negative predictive value of ERUS in predicting CRM were the highest (100%, 98.2%, 100%). The diagnostic accuracies of ERUS among different positions, distances from the anal verge, and stages were not significantly different (P>0.05).

  Conclusion  ERUS can accurately predict CRM, with a high negative predictive value, which can provide reliable information for assessment of prognosis and formulation of clinical treatment plan.