A Comparison of Liver MRI and Contrast-Enhanced CT as Standard Workup Before Treatment for Rectal Cancer in Usual Care - A Retrospective Study.

Background: The liver is the most common site for rectal cancer metastases. Recommended standard pre-treatment workups have involved Computed Tomography (CT) for abdominal metastases, however, few hospitals have replaced this with Magnetic Resonance Imaging (MRI).

Introduction: The aim of this study was to compare MRI with CT as an index examination of the liver in the pre-treatment workup in usual care. The primary endpoint was the need for supplementary liver investigations.

Methods: Consecutive patients from two hospitals during 2013-2015 were identified in the Regional Swedish Colorectal Cancer Register and included in this retrospective study. Hospital records and radiology reports were reviewed. Inconclusive reports were re-evaluated by two radiologists.

Results: A total of 320 patients were included, and 293 were available for analysis. Some 175 and 118 patients had undergone CT and MRI respectively, as their index pre-treatment liver examination. Thirty-four (19.4%) in the CT group and 6 (5.1%) patients in the MRI group underwent supplementary liver investigation due to inconclusive index examination (RR 3.82, 95% CI: 1.66; 8.81, p=0.0017). Median time (q1; q3) from index examination to start of treatment was 50 (36; 68) days in the CT group and 34 (27; 45) days in the MRI group.

Conclusion: This retrospective study of two modalities within usual care found that MRI of the liver as index radiological workup before treatment for rectal cancer was associated with fewer supplementary liver investigations and a shorter time to start of treatment. Based on these findings, a prospective trial should be undertaken before implementing MRI as a standard. Clinicaltrials.gov Registration Number: NCT03463616.