Introduction: Incomplete myelination during early life limits direct cortical electrical stimulation (DCES) effectiveness and subsequent motor mapping. Higher stimulation thresholds and repeated attempts, especially in epileptic children, can provoke seizures, edema and cortical injury. Diffusion tensor image (DTI) based tractography measures changes in water diffusion and fractional anisotropy between white/gray matter. Transcranial magnetic stimulation (TMS) approximates motor cortex by measuring electromyographic responses. Both modalities can map motor pathways during surgical planning. Here, we tested whether DTI and TMS could accurately localize Rolandic cortex in young children with immature white matter.
Methods: Motor pathway localization by pre-operative DT tractography was conducted in 17 children who were undergoing surgery for resection of epileptic foci. Four patients also had motor cortex identified by preoperative TMS. Intraoperative electrocorticographic recordings were used to localize the central sulcus at the point of phase reversal between the primary
sensory and motor cortices. This location was identified on stereotactic neuronavigation imaging and compared to pathways predicted by preoperative DTI and TMS.
Results: The average subject age was 2.5 years. In all 17 cases, DT tractography accurately identified the motor cortex in relation to the central sulcus confirmed by intraoperative phase reversal-based localization of the central sulcus and motor mapping. The 3 patients undergoing TMS had accurate trilocalization of their motor cortex as well.
Conclusions: DTI and TMS are accurate for central sulcus localization as demonstrated by electrocorticographic localization in very young children still undergoing active myelination. They may eliminate the need for DCES and its associated risks.
Patient Care: It could prevent children from being exposed to the risks of DCES when undergoing motor cortex localization and improve surgical planning pre-operatively.
Learning Objectives: By the conclusion of this session, the participant should have a solid understanding of the methods of localization of the motor cortex during epilepsy surgery including TMS, DTI, and DCES and their effectiveness in young children undergoing active myelination.