gms | German Medical Science

Objective: The extent of resection in cerebral gliomas is considered to be of critical importance to increase patient's overall survival. For this purpose, advanced imaging techniques such as DTI based tractography are important to depict the relation between white matter fibers and tumor. The use of this tool combined with intraoperative high-field MRI (iopMRI) opens the possibility to update this information during surgery. Our aim is to verify fiber-tracking reliability using direct electrical subcortical stimulation (DES) during glioma surgery in the iopMRI environment.

Method: We report preliminary results of 5 consecutive patients treated at our institute for gliomas located near the CST using iopMRI (1.5 T). The patients were preoperatively studied using an MR protocol including DTI. After every intraoperative imaging control the CST was reconstructed using the navigation software (Brainlab) to obtain updated images with the exact relation of the CST to the residual lesion and/or resection cavity. DES was performed with a bipolar electrode at 50Hz right after the image update under the guidance of the updated navigation system. This allowed to precisely document the position the bipolar electrode tip in relation to the resection cavity and the DTI tractography based CST.

Results: The cases included 4 GBM and one low grade glioma. All patients suffered preoperatively from motor deficits. The tumors were in close proximity to the CST causing displacement and morphological changes compared to the healthy side. DES resulted in positive motor responses in four cases at the location of the DTI-based reconstruction of the CST. All of these 4 patients experienced a progressive improvement of the preoperative motor weakness, starting at the immediate postoperative course. DTI tractography also displayed a normalization of CST anatomy in terms of position and volume related to the neurological improvements after tumor removal. In one case, DES with an intensity of 3-12 mA showed no positive motor response, however, DTI tractography demonstrated an anatomically accurate location of CST adjacent to the resection border. This DTI based information was respected and no further resection towards the CST was performed. After surgery the preoperative motor weakness was improved significantly. The volume of resection was more than 95% in all cases.

Conclusions: These preliminary results indicate that the iop-DTI based location of the CST correlates with DES evoked positive motor responses.