Preoperative Imaging to Predict Intraoperative Changes in Tumor-to-Corticospinal Tract Distance

Abstract

Preoperative diffusion tensor imaging (DTI) is used to demonstrate corticospinal tract (CST) position. Intraoperative brain shifts may limit preoperative DTI value, and studies characterizing such shifts are lacking. To examine tumor characteristics that could predict intraoperative shift in tumor-to-CST distance using high-field intraoperative magnetic resonance imaging. We retrospectively evaluated preoperative and intraoperative DTIs, tumor pathology, and imaging characteristics of patients who underwent resection of an intra-axial tumor adjacent to the CST to identify covariates that significantly affected shift in tumor-to-CST distance. For validation, we analyzed data from a separate, 20-patient cohort. In the first cohort, the mean intraoperative shift in the tumor-to-CST distance was 3.18 ± 3.58 mm. The mean shift for the 20 patients with contrast and the 5 patients with non-contrast-enhancing tumors was 3.93 ± 3.64 and 0.18 ± 0.18 mm, respectively (P < .001). No association was found between intraoperative shift in tumor-to-CST distance and tumor pathology, tumor volume, edema volume, preoperative tumor-to-CST distance, or extent of resection. According to receiver-operating characteristic analysis, nonenhancement predicted a tumor-to-CST distance shift of ≤ 0.5 mm, with a sensitivity of 100% and a specificity of 75%. We validated these findings using the second cohort. For nonenhancing intra-axial tumors, preoperative DTI is a reliable method for assessing intraoperative tumor-to-CST distance because of minimal intraoperative shift, a finding that is important in the interpretation of subcortical motor evoked potential to maximize extent of resection and to preserve motor function. In resection of intra-axial enhancing tumors, intraoperative imaging studies are crucial to compensate for brain shift.