Abstracts

Rationale: Children with pharmacologically refractory epilepsy may require an invasive surgical evaluation. Although subdural electrodes are commonly used to identify the seizure onset zone, their success in localizing a deep focus is limited. We identified 4 pediatric cases with developmental lesions, where the addition of depth electrodes to subdural electrodes, provided essential information to aid resection during invasive EEG monitoring. Methods: Four patients who underwent an invasive surgical evaluation that included depth electrodes placed in the structural lesion, were retrospectively identified at Boston Children s Hospital between 2010 and 2012. Information regarding epilepsy history, imaging, neurophysiologic data, surgery and outcomes were reviewed with approval by the institutional review board at Boston Children s Hospital.Results: Four patients were identified with developmental lesions over the frontal (2) and temporal (2) regions. Subdural recordings in these cases showed diffuse seizure onsets in 3 of the 4 patients while no ictal rhythm was detected in the fourth patient. Some of the subdural electrodes were recording over eloquent cortex. On the other hand, depth electrodes placed in the lesion were able to identify early ictal onsets in the depth of the lesion thereby providing vital information for successful surgical planning. No complications were noted related to placement of the intracranial electrodes. No patient was noted to have permanent motor/language deficit. Three of 4 cases (cases 1-3), had EEG changes at onset that were very widespread and not well-localized on subdural electrodes; however, EEG changes such as focal spikes and attenuation were seen in the depth electrodes preceding the widespread EEG changes on subdural electrodes. In the remaining one case, EEG changes at seizure onset were limited to the depth electrode only. Conclusions: In all four cases, depths electrodes were very helpful in localizing the seizure onset zone and aided in performing a targeted resection, ultimately leading to favorable seizure outcomes with no or minimal transient neurological deficits. In cases of developmental lesions, the seizure focus may be deep and subdural electrodes alone may be insufficient to accurately localize the focus. The addition of depth electrodes in these cases allowed accurate and detailed localization of the ictal onset zone. This information played an important role in tailoring the resection, ultimately maximizing chances of seizure control and avoiding surrounding eloquent cortex to minimize risks of neurological deficits.