Variations in Pelvic Dimensions Do Not Predict the Risk of Circumferential Resection Margin (CRM) Involvement in Rectal Cancer

BACKGROUND: The objective of this study was to assess the value of preoperative pelvimetry, using magnetic resonance imaging (MRI), in predicting the risk of an involved circumferential resection margin (CRM) in a group of patients with operable rectal cancer. METHODS: A cohort of 186 patients from the MERCURY study was selected. These patients' histological CRM status was compared against 14 pelvimetry parameters measured from the preoperative MRI. These measurements were taken by one of the investigators (G.S.), who was blinded to the final CRM status. RESULTS: There was no correlation between the pelvimetry and the CRM status. However, there was a difference in the height of the rectal cancer and the positive CRM rate (p = 0.011). Of 61 patients with low rectal cancer, 10 had positive CRM at histology (16.4% with CI 8.2%-22.1%) compared with 5 of 110 patients with mid/upper rectal cancers (4.5% with CI 0.7%-8.4%). CONCLUSIONS: Magnetic resonance imaging can predict clear margins in most cases of rectal cancer. Circumferential resection margin positivity cannot be predicted from pelvimetry in patients with rectal cancer selected for curative surgery. The only predictive factor for a positive CRM in the patients studied was tumor height.