gms | German Medical Science

The goal of this study was to use functional magnetic resonance (fMRI) and diffusion tensor imaging (DTI) to track fibers combined with intraoperative electrophysiological mapping to delineate subcortical pathways between cortical language sites associated with motor speech and naming. This information was expected to guide tumor resection and to prevent surgical morbidity.

Five patients with different intracranial lesions adjacent to the inferior frontal cortex received presurgical imaging with fiducial markers for intraoperative image guidance MR images were acquired on a high-field 3.0 T scanner. For the fMRI examination, EPI sequence was used to image the whole brain volume in axial rotation while the patients performed different language tasks (e.g. verb generation and picture naming).The reference anatomical sequence was a T1-weighted MPRANGE series.The DTI data was acquired with an EPI sequence with axial slices covering the brain from the pons to the vertex. Data sets were reconstructed, motion-corrected and re-aligned using SPM2. Fiber tracking was processed using DTiMap (Mori, Baltimore). Co-registration and 3D visualization of structural and functional information was performed with BrainVoyager QX. Electrophysiological mapping was performed during awake surgery using a bipolar probe. The patients underwent neuropsychological language testing before, throughout and after the procedure.

In all patients, the combination of reconstructed and fused fMRI and DTI data provided useful information concerning the topographical tumor interaction with corical language sites and connecting subcortical fiber bundles. Intraoperative mapping confirmed the preoperative images and detailed the relationships between eloquent sites and tumor boundaries. Subcortical stimulations could be regularly applied along the procedure terminating further resections whenever eliciting speech arrest and anomia. None of the patients showed additional permanent motor speech deficits after surgery.

The fusion of fMRI and DTI data is a helpful additional source of information concerning surgery in the vicinity of functional language areas and their connecting fibre bundles associated with motor speech and naming. Subcortical electrophysiological mapping is essential in detecting functional pathways in the white matter. Thereby, this technique may serve as a tool to validate preoperative imaging which still remains limited by intraoperative brain shift.