In Tractography We Trust? An Intraoperative Assessment of the Accuracy/Reliability of MRI Brain Tractography During Tumor Resection

Introduction: MRI brain tractography is an emerging technology that allows for visualization of white matter tracts in vivo, that can aid with intracranial tumor resection, however, the reliability of this technology is unknown. This study evaluates the accuracy of MRI tractography during intraoperative tumor resection in the cortical and subcortical space.

Methods: Ten patients with intrinsic brain tumors involving the motor strip were evaluated. White matter tractography data, visually depicting the ipsilateral corticospinal tract, obtained in the preoperative MRI, was exported to the stereotactic neuronavigation system, allowing for intraoperative visualization of the corticospinal tract. Direct cortical stimulation motor mapping was used intraoperatively as the gold standard for identifying eloquent motor areas.
Prior to tumor resection, designated areas of the cortical surface at the margins of the tumor, that did and did not have visual indications of eloquence, based on cortical spinal tract tractography, were stimulated to determine motor response. Subcortical stimulation was conducted during tumor resection in a similar fashion. Sensitivity, specificity, positive and negative predictive values were generated from this data.

Results: Mean age for the patient series was 66.2 (SD=7.7) years old. Sixty percent of lesions were in the left hemisphere. Preoperative and postoperative Karnofsky performance score (KPS) was 78 (11.7) and 80 (10.9), respectively (p=0.71). Mean preoperative tumor volume was 10.5cm3 and mean extent of resection was 96.1% (7.7). Cortical MRI tractography predicted eloquence at 93% sensitivity, 100% specificity, 100% positive predictive value, and 92% negative predictive value. Subcortical MRI tractography had a 71% sensitivity, 100% specificity, 100% positive predictive value, and 62% negative predictive value.

Conclusion : Intraoperative use of MRI tractography to evaluate for eloquent white matter tracts provides a viable option to visually identify white matter tracts intraoperatively, but may still benefit from concurrent use of supplemental cortical/subcortical stimulation in areas where tracts are not visually identified with intraoperative tractography.