A prospective comparison of endorectal ultrasound and pelvic magnetic resonance in the preoperative staging of rectal cancer.

Background: The development of new surgical modalities (local excision, coloanal-anastomosis) and the diffusion of preoperative neoadjuvant therapy, has increased the importance of an accurate preoperative staging in patients with rectal cancer. The aim of this study was to compare the accuracy of endoscopic ultrasound (EUS) and magnetic resonance imaging (MRI) in the local preoperative staging of rectal carcinoma; moreover the two methods were assessed with a concordance K test.

Methods: Twenty-nine patients with rectal carcinoma were staged with EUS and body coil MRI and then underwent radical surgery. The preoperative staging was compared with the histologic findings of the operative specimen.

Results: EUS was more accurate (79.3%), with better sensibility (90%), positive predictive value (PPI9 (85.7%) and negative predictive value (NPV) (25%) than MRI in the evaluation of T parameter. MRI was more accurate (72.4%), with better specificity (81.2%), PPV (72.7%) and NPV (68.4%) than EUS in the evaluation of N parameter. The concordance test obtained a K value of 19.8% for the T parameter and 34.2% for the N parameter.

Conclusions: EUS and MRI are complementary methods in the preoperative staging of rectal cancer. EUS is more accurate in determining bowel wall penetration of the tumor, while MRI is more accurate in the evaluation of lymph node involvement. The low value of the K index confirms the complementarity of the two examinations. Further studies with new imaging techniques such as endocoil MRI, external phase-arrayed coil MRI and three dimensional ultrasound are needed to identify the most effective single examination in the preoperative staging of rectal cancer.