Current value of intraoperative electrocorticography (iopECoG).

Objective: Intraoperative electrocorticography (iopECoG) can contribute to delineate the resection borders of the anticipated epileptogenic zone in epilepsy surgery. However, it has several caveats that should be considered to avoid incorrect interpretation during intraoperative monitoring.

Methods: The literature on iopECoG application was reviewed, and pros and cons as well as obstacles to this technique were analyzed.

Results: The literature of the first half of the nineties was very enthusiastic in using iopECoG for tailoring the resection in temporal as well as extratemporal epilepsy surgery. Mostly, this resulted in a good correlation of postresection ECoG and excellent seizure outcome. In the second half of the nineties, many authors demonstrated lack of correlation between iopECoG and postoperative seizure outcome, especially in surgery for temporal lobe epilepsy with hippocampal sclerosis. In the noughties, investigators found that ECoG was significantly useful in neocortical lesional temporal lobe epilepsy as well as in extratemporal lesional epilepsies. Extratemporal epilepsy without lesions proved to be more a domain of chronic extraoperative ECoG, especially using depth electrode recordings. In recent years, iopECoG detecting high-frequency oscillations (ripples, 80-250 Hz, fast ripples, 250-500 Hz) for tailored resection was found to allow intraoperative prediction of postoperative seizure outcome.

Conclusion: After a period of scepticism, iopECoG seems back in the focus of interest for intraoperative guidance of resecting epileptogenic tissue to raise postoperative favorable seizure outcome. In temporal and extratemporal lesional epilepsies, especially in cases of focal cortical dysplasia, tuberous sclerosis, or cavernous malformations, an excellent correlation between iopECoG-guided resection and postoperative seizure relief was found.