Background: Accuracy of MRI in assessing mesorectal fascia and predicting circumferential resection margin decreases in low anterior rectal tumors.
Objective: The purpose of this work was to evaluate the accuracy of endorectal ultrasound in predicting the pathologic circumferential resection margin in low rectal anterior tumors and to compare it with MRI findings.
Design: This was a prospective series comparing the preoperative circumferential resection margin assessed by endorectal ultrasound and MRI with pathologic examination.
Settings: The study was conducted by a specialized colorectal multidisciplinary team at a tertiary teaching hospital.
Patients: Between 2002 and 2008, 76 patients with mid to low rectal cancer were preoperatively evaluated by endorectal ultrasound and MRI and underwent total mesorectal excision without neoadjuvant radiochemotherapy. Twenty-seven patients with posterior or postero-lateral tumors were excluded, leaving 49 patients with anterior or antero-lateral tumors for the present subanalysis. We compared preoperative circumferential resection margin status using endorectal ultrasound and MRI with pathologic examination.
Interventions: We conducted a comparison between preoperative circumferential resection margin status and pathologic examination after total mesorectal excision surgery.
Main outcome measures: Accuracy in predicting pathologic circumferential resection margin status was measured.
Results: Overall accuracy of endorectal ultrasound and MRI in assessing circumferential resection margin status was 83.7% and 91.8%, with negative predictive values of 97.2% and 97.5%. When focusing on low rectal tumors, the overall accuracy of endorectal ultrasound increased to 87.5%, whereas the accuracy of MRI decreased to 87.5%, with a negative predictive value of 95.6% for both diagnostic tests.
Limitations: The sample size is small, and interobserver variability in radiologic assessment was not evaluated.
Conclusions: Endorectal ultrasound can help MRI in predicting circumferential resection margin involvement in mid to low anterior rectal cancer, especially at the low third of the rectum, with a high negative predictive value.