| Intraoperative Electrocorticography and Functional Brain Mapping in Epilepsy Surgery |
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Eun-Ik Son |
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Department of Neurosurgery, Keimyung University School of Medicine, Daegu, Korea |
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| Abstract |
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Planning a resection for epilepsy involves both identification of the tissue generating seizures and also those essential areas where a resection is likely to lead to an unacceptable neurologic deficits. The essential areas of great concern are usually those subserving motor and language function. The most commonly used method for identifying essential areas is an anatomic topographic approach. But, the anatomic landmarks do not provide complete security that essential areas have not been resected, as indicated by an occasional language deficit after measured anterior temporal lobe. The alternative method for identification is electrical stimulation mapping. Application of electric current to cortical surface has both excitatory and inhibitory effects on neuronal populations and passage fibers, both locally and at a distance. Empirically, language responses seem to represent a predominance of inhibitory effects, most likely from temporary inactivation of neurons by depolarizing blockade, on the other hand, sensorimotor responses represent as an excitatory effects. Regards to the threshold for afterdischarge, Engel has maintained that threshold is higher in relatively damaged unfunctional epileptic cortex, others have thought that low thresholds are an indication of epileptogenicity, but afterdischarge thresholds are much less reliable in determining the epileptogenic area than positive clinical responses. Stimulation mapping of language and motor require an awake and alert patient, provided intraoperatively by use of local anesthetics in the scalp as a field block, and an ultrashort acting intravenous anesthetic, propofol, for craniotomy. Although lateral and basal cortical surface stimulation seems to provide the information needed to plan a resection, there is some evidence that it does not identify all of the cortex essential for language even in the temporal lobe. Intraoperative electrocorticographic (ECoG) recording and functional mapping of adjacent areas of epileptogenic area are useful in epilepsy surgery and can guide the extent of appropriate tailored resection. |
| Key Words:
Epilepsy, Awake evaluation, Electrical stimulation, Functional brain mapping, Electrocorticographic (ECoG) recording. |
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