Abstracts

Rationale: Prior to surgery for intractable epilepsy, it is of vital importance that the brain be appropriately mapped to localize areas of functional significance. Non-invasive methods for mapping include electroencephalography (EEG), magnetoencephalography (MEG) and functional MRI (fMRI). However, the gold standard for mapping is an invasive procedure referred to as electrical stimulation mapping (ESM). More recently, the advent of Real-Time Functional Mapping (RTFM) based on electrocorticography (ECoG) has been shown to detect areas of the eloquent cortex as well. In this study, we focused on eight cases in which RTFM detected language function in areas not evaluated by ESM. Analysis of these data is imperative to determine whether RTFM could have provided more information regarding language function in addition to that of ESM. Methods: All eight of our patients underwent both ESM and RTFM evaluations with various language paradigms prior to surgical resection for epilepsy. Offline analyses were performed to identify electrodes that were not stimulated by ESM yet tested positive for language function using RTFM (non-stimulated RTFM (+) electrodes). ESM positive electrodes (ESM (+)) were calculated as a percentage of the total grid electrodes. Non-stimulated RTFM (+) electrodes were calculated as a percentage of total grid electrodes. This was performed for each patient. A cumulative calculation was generated. In addition, the amount of non-stimulated RTFM (+) electrodes, which were surgically resected, was calculated as a percentage of total non-stimulated RTFM (+) electrodes. Results: Our studies revealed that each of our 8 patients had electrodes that were not stimulated using ESM which were RTFM positive for language function. Six of eight patients had greater than 10% non-stimulated RTFM (+) electrodes in addition to electrodes positive for language via ESM. 4 of 8 patients had a portion of non-stimulated RTFM (+) electrodes surgically resected as well. Cumulatively, 16% of the total mapping grid electrodes were ESM (+) and 17% were non-stimulated RTFM (+). 15% of the ESM (+) electrodes were resected while 10% of non-stimulated RTFM (+) electrodes were resected. Conclusions: Our study revealed the following: (1) Areas of the electrode grid that were not stimulated via ESM yet found to be positive using RTFM. This suggests that the remaining electrodes may have additive potential to ESM in detecting areas of functional significance; (2) Our data suggest that surgical resection may be potentially compromising/sacrificing areas of eloquent language cortex that are not always captured by ESM. Future perspectives: The implications of resecting these RTFM (+) electrodes that were not evaluated by ESM will be further analyzed in relation to results of post-surgical neuropsychological evaluations. Following this correlative analysis, clinical significance of the RTFM's additive potential will be determined. Additive values of other imaging modalities, such as fMRI and MEG will be determined as well.