The added value of diffusion-weighted magnetic resonance imaging (DW-MRI) in the local staging of advanced colorectal pelvic cancer.

Abstract

378 Background: Surgeons rely on imaging to plan exenterative pelvic surgery for locally advanced primary and recurrent rectal cancer. Accurate local staging is vital in this process, as it provides information about the extent of the disease, facilitating the planning of the operation required to achieve complete resection. DW-MR imaging is a functional radiological modality that can provide indirect informationabout the water proton mobility within biologic tissue, without the need of a contrast agent. The aim of the present study was to assess the diagnostic accuracy and added value of diffusion DW-MRI in detecting colorectal tumor invasion into seven intrapelvic compartments for planning exenterative pelvic surgery. Methods: Thirty three consecutive patients were preoperatively staged using DW-MRI to undergo exenterative surgery for locally advanced primary (n=12) and recurrent (n=21) colorectal pelvic cancer. Two radiologists reported tumor invasion for each of the seven anatomic surgical resection compartments and were blinded to histopathology and intraoperative reference standards. Accuracy, sensitivity, specificity and predictive values were calculated for the seven intrapelvic compartments. Interobserver agreement was assessed using Cohen's Kappa (k) coefficient for each compartment. Results: The sensitivity of DW-MRI when used alone was low for all the compartments except the central (92%). Its specificity was very high for all the compartment (≥89.5%). Combining DW-MRI with conventional MRI increased the sensitivity for the lateral compartment by 8.3% to 100% and the specificity for the anterior compartment below the peritoneal reflection by 9.1% to 90.9%. The overall incremental value for the lateral compartment was 3%. The interobserver agreement was either good or very good (k≥0.669; p<0001) for all the compartments. Conclusions: DW-MRI can improve the diagnostic accuracy of conventional MRI when staging patients with advanced colorectal pelvic cancer. Diffusion images are cheap and easy to obtain. Therefore DW-MRI should always be used in combination with conventional MRI when considering patients for exenterative pelvic surgery. No significant financial relationships to disclose.