Abstracts

Magnetic source imaging (MSI) is a combination of magnetic sources of evoked responses and epileptic discharges coregistered with structural magnetic resonance images (MRI). A combination of MSI data and intraoperative neuronavigation system has been developed to inform the exact location on the real-time functional mapping in patients with lesions around the motor cortex. We report a systematic study regarding clinical applications of this technique in surgical treatment for intractable epilepsy.
We studied magnetoencephalography (MEG) to obtain somatosensory evoked fields (SEF) and interictal spikes in 16 patients with (14 patients) or without lesions (2 patients). MEG data were overlaid onto individual T1 weighted MRI. We converted MSI data on a neurosurgical flameless stereotaxy system in the operating room. Central sulcus (CS) was identified using intraoperative somatosensory evoked potential (SEP) and/or cortical stimulation in cases of epileptic zone around the CS. Epileptic zone was demarcated by intraoperative electrocorticograpy (ECoG) and/or chronic intracranial video-EEG (IVEEG) prior to the ECoG. We compared the epileptic zone on the exposed brain surface to 3D-reconstructed MEG epileptic zones on the intraoperative navigation system. We also analyzed the correlation of the SEF location on 3D-reconstructed MSI with the results of the SEP and/or cortical stimulation.
All 16 patients underwent cortical excision in 11 patients, lesionectomy alone in 4 patients, and hemispherectomy in 1 patient. Intraoperative ECoG and IVEEG were performed in 12 patients. The epileptic zone was located around the sensorimotor cortex in 6 patients. SEF navigated the sensory cortex in 5 of the 6 patients. The navigated sensory cortex along with CS was highly correlated with the sensorimotor cortex identified by intraoperative SEP and/or cortical stimulation. MEG spike sources were obtained in 12 patients. Eight patients who had spikes on both MEG and intraoperative ECoG showed colocalized the epileptogenic zone. In the 8 patients, the distribution of MEG spike sources were highly correlated with intracranial EEG spikes in the ipsilateral hemisphere with a mean of 97.7 % (91.3-100%), excluding mirror foci.
3D-reconstrated MSI data for intraoperative navigation system can precisely localize functional and epileptic regions on the exposed brain surface. This technique allows the neurosurgeons to plan the optimal preoperative trajectory and to perform intraoperative demarcation of the epileptogenic region, especially around the functional cortex.