P16.11 * A NEW TECHNIQUE OF "FUNCTIONAL" DTI TRACTOGRAPHY OF THE CORTICO-SPINAL TRACT BASED ON NAVIGATED BRAIN STIMULATION FOR SURGERY OF BRAIN TUMORS LOCATED NEAR THE MOTOR PATHWAY
Authors: A. Conti, G. Raffa, A. Germano, F. Granata, A. Quartarone, V. Rizzo, C. Terranova, M. Longo, F. Tomasello
Journal: Neuro-Oncology (2014)

INTRODUCTION: Surgery of brain tumors located near the motor pathway still represents a challenge because of the risk of significant post-operative morbidity. In the last few years, there have been an increasing interest for imaging techniques that could reliably define the spatial relationship between a tumor and the adjacent eloquent areas before surgery. Among these techniques, navigated brain stimulation (NBS) and DTI tractography of the cortico-spinal tract (CST) are considered the most promising. However, tractography still presents spatial inaccuracies that can be reduced by using the NBS map of the motor cortex as seeding region for the tract reconstruction. The objective of this study is to: describe a new technique of a “functional” NBS-based DTI tractography of the CST able to define its somatotopic organization; verify its accuracy by using direct subcortical stimulation (DSS); compare its reliability with the standard tractography; assess its impact on surgical strategy and motor outcome in patients operated for brain tumors located near the motor pathway. MATERIALS AND METHODS: We prospectively enrolled patients operated at the Neurosurgical Clinic of the University of Messina, Italy, between 2012 and 2014. All patients were submitted to the “functional” NBS-based DTI tractography of the CST. We reconstructed the motor pathway pre- and intra-operatively for the surgical planning as a guide for the lesion resection. In addition, after surgery, we performed the standard CST tractography. We assessed the accuracy of the CST somatotopic reconstruction using the DSS. Then, we compared the reliability of our technique with the standard tractography, analyzing the number of tract fibers obtained using the two techniques and the degree of overlapping of the CST cortical end-regions with the NBS map of the motor cortex. Lastly, we assessed the impact of our technique on surgical strategy using a multiple choice questionnaire provided to the surgeon, and assessed its efficacy in avoiding post-operative motor deficits using the Medical Research Council (MRC) scale. RESULTS: In 25 cases cases we obtained a somatotopic reconstruction of the CST, distinguishing between functionally different fiber bundles (arm, face and leg fibers) which matched with the DSS. The “functional” technique was more accurate than the standard tractography, providing useful information to the surgeon in 76% of cases. Lastly no worsening of the MRC score was recorded in all cases. CONCLUSIONS: The “functional” NBS-based DTI tractography of the CST is a reliable planning tool for surgery of brain tumors located near the motor pathway. It provides helpful anatomical and functional information about the motor pathway that can be used before and during surgery. It is also more accurate and less operator-dependent as compared to the standard tractography and is effective in avoiding post-operative motor deficits.