Comparison of the value between computed tomography and magnetic resonance imaging in reassessment of the T-stage of rectal cancer after neoadjuvant therapy

Abstract

Introduction: Staging assessment plays an important role in choosing the optimal treatment method for patients with rectal cancer. Especially in the case of neoadjuvant chemoradiation, this affects the surgical method, for example local or total rectal resection.
Purpose: Comparing the value of computed tomography and magnetic resonance imaging in predicting local tumor stage (yT), regional lymph node metastasis and Circumferential resection margin (yCRM) after neoadjuvant chemoradiation.
Methods: Cross-sectional study on 62 rectal cancer patients who underwent CT and MRI before and after neoadjuvant chemoradiation with a long course, surgery and pathology results at Ho Chi Minh City University  of Medicine and Pharmacy Hospital. The disease stage was reassessment before surgery on CT and MRI, compared with pathology results with a complete description of ypT stage, lymph node metastasis, and ypCRM.
Results: The value of CT and MRI to evaluate non-T0 stages is not different. Both diagnostic tools have high sensitivity, positive predictive value, and accuracy in assessing non-T0 stages. CT and MRI both have high specificity, accuracy and negative predictive value in assessing stage T4 (82 - 94.5%). Regarding overall accuracy, CT is lower than MRI in assessing T stage (38.7 vs. 54.8%). In assessing lymph nodes metastasis, CT and MRI do not have a clear difference in value. Both have quite good negative predictive values, approximately 80%. CT and MRI both have high negative predictive value in assessing mesorectal fascia invasion, approximately 95% and MRI has 11-13% higher specificity and accuracy than CT. 
Conclusions: After neoadjuvant therapy, CT and MRI both show good reliability in detecting remaining tumor, so a "watch and wait" strategy can be considered for cases where the tumor is no longer visible. Both have good reliability to exclude stage yT4, regional lymph node metastasis and mesorectal fascia invasion.