Objectives: This study assesses the ability of body coil magnetic resonance imaging (MRI) to pre-operatively stage mural penetration, nodal status and circumferential resection margin (CRM) involvement of rectal cancer.
Patients and methods: Between 1995 and 1997, MRI using a body coil was performed in consecutive patients with primary rectal carcinomas. Group A: 67 patients underwent surgery without long course neo-adjuvant therapy. Predicted tumour stage was compared to the histology of the specimen. Group B: 21 patients with MRI evidence of advanced disease, underwent long course neo-adjuvant therapy followed by repeat MRI prior to surgery. The second scan assessed response to treatment and likelihood of CRM involvement at subsequent surgery.
Results: Group A: Accuracy of pre-operative staging was: 'T' stage - 54%, 'N' stage - 77%, involvement of CRM by tumour - 97%. Group B: After long course neo-adjuvant therapy the second MRI scan was 95% accurate in predicting CRM involvement by tumour.
Conclusion: In this study pre-operative rectal cancer staging with MRI and a body coil lacks accuracy in predicting mural penetration and nodal involvement. Body coil MRI can accurately predict the potential for CRM involvement. This technique may help determine which patients require long course neo-adjuvant therapy.