Abstract：Objective: To evaluate the accuracy of preoperative MRI in prediction of pathological staging and involvement of circumferential resection margin(CRM) in rectal cancer. Methods: Twenty-eight patients were biopsy-proven to be rectal cancer through preoperaitive colonoscopy. All patients were inserted with a triple cavity catheter with balloon inflated with air to the anus before MRI examining, Siemens Magnetom Avanto 1.5T were used. All patients underwent total mesorectal excision and were assessed prospectively using high-resolution MRI for tumour(T) and mesorectal nodal(N) staging as well as CRM status using the depth of tumour spread, tumour node metastasis and CRM involvement. Preoperative MRI assessment of these prognostic factors was compared with the histopathological findings by carefully correlated with pathologic specimen. Results: MRI correctly staged the tumor in 24 patients, had 4 mistakes, understaged in 1 case, and overstaged in 3 cases. The accuracy of T stage was 85.7%(24/28). There was an accurate correlation between pathologic and MRI tumor staging(Kappa=0.773, P<0.001). Node status was correctly staged in 22 patients, overstaged in 4 cases, and understaged in 2 cases. The accuracy of node staging was 78.6%(22/28), sensitivity was 89.5%(17/19), and specificity was 55.6%(5/9). The correlation between pathologic and MRI node staging was generic(Kappa=0.478, P=0.01). The CRM status was correctly reported in 26 patients, overstaged in 1 case, and understaged in 1 case. The accuracy of CRM status was 92.9%(26/28), sensitivity was 85.7%(6/7), and specificity was 95.2%(20/21). There was a good correlation between pathologic and MRI CRM involvement(Kappa=0.81, P<0.001). Conclusion: Preoperative MRI provides generic predictive data as to mesorectal node stage, but does produce reliable prediction of clear CRM and tumor staging.
2011, Vol. 22 
