Pediatric epilepsy surgery: Toward increased utilization and reduced invasiveness

Clinical Utility of Transcranial Magnetic Stimulation (TMS) in the Presurgical Evaluation of Motor, Speech, and Language Functions in Young Children With Refractory Epilepsy or Brain Tumor: Preliminary Evidence

Accurate presurgical mapping of motor, speech, and language cortices, while crucial for neurosurgical planning and minimizing post-operative functional deficits, is challenging in young children with neurological disease. In such children, both invasive (cortical stimulation mapping) and non-invasive functional mapping imaging methods (MEG, fMRI) have limited success, often leading to delayed surgery or adverse post-surgical outcomes. We therefore examined the clinical utility of transcranial magnetic stimulation (TMS) in young children who require functional mapping. In a retrospective chart review of TMS studies performed on children with refractory epilepsy or a brain tumor, at our institution, we identified 47 mapping sessions in 36 children 3 years of age or younger, in whom upper and lower extremity motor mapping was attempted; and 13 children 5–6 years old in whom language mapping, using a naming paradigm, was attempted. The primary hand motor cortex was identified in at least one hemisphere in 33 of 36 patients, and in both hemispheres in 27 children. In 17 children, primary leg motor cortex was also successfully identified. The language cortices in temporal regions were successfully mapped in 11 of 13 patients, and in six of them language cortices in frontal regions were also mapped, with most children (n = 5) showing right hemisphere dominance for expressive language. Ten children had a seizure that was consistent with their clinical semiology during or immediately following TMS, none of which required intervention or impeded completion of mapping. Using TMS, both normal motor, speech, and language developmental patterns and apparent disease induced reorganization were demonstrated in this young cohort. The successful localization of motor, speech, and language cortices in young children improved the understanding of the risk-benefit ratio prior to surgery and facilitated surgical planning aimed at preserving motor, speech, and language functions. Post-operatively, motor function was preserved or improved in nine out of 11 children who underwent surgery, as was language function in all seven children who had surgery for lesions near eloquent cortices. We provide feasibility data that TMS is a safe, reliable, and effective tool to map eloquent cortices in young children.

Concordance Between Transcranial Magnetic Stimulation and Functional Magnetic Resonance Imaging (MRI) Derived Localization of Language in a Clinical Cohort

Transcranial magnetic stimulation (TMS) is a newer noninvasive language mapping tool that is safe and well-tolerated by children. We examined the accuracy of TMS-derived language maps in a clinical cohort by comparing it against functional magnetic resonance imaging (MRI)-derived language map. The number of TMS-induced speech disruptions and the volume of activation during functional MRI tasks were localized to Brodmann areas for each modality in 40 patients with epilepsy or brain tumor. We examined the concordance between TMS- and functional MRI-derived language maps by deriving statistical performance metrics for TMS including sensitivity, specificity, accuracy, and diagnostic odds ratio. Brodmann areas 6, 44, and 9 in the frontal lobe and 22 and 40 in the temporal lobe were the most commonly identified language areas by both modalities. Overall accuracy of TMS compared to functional MRI in localizing language cortex was 71%, with a diagnostic odds ratio of 1.27 and higher sensitivity when identifying left hemisphere regions. TMS was more accurate in determining the dominant hemisphere for language with a diagnostic odds ratio of 6. This study is the first to examine the accuracy of the whole brain language map derived by TMS in the largest cohort examined to date. While this comparison against functional MRI confirmed that TMS reliably localizes cortical areas that are not essential for speech function, it demonstrated only slight concordance between TMS- and functional MRI-derived language areas. That the localization of specific language cortices by TMS demonstrated low accuracy reveals a potential need to use concordant tasks between the modalities and other avenues for further optimization of TMS parameters.