Surgical outcome of MRI-negative refractory extratemporal lobe epilepsy

- Surgery is a valuable option for patients with intractable MNETLE, at the time of latest follow-up, 13 (46.4%) patients were seizure-free (ILAE1) and 18 (64.3%) had a good (ILAE 1, 2, 3) outcome.
- Having ≥120 electrode contacts in the evaluation is an independent variable predicting seizure freedom. A larger (> 120 electrodes) study may improve chances of seizure freedom, contingent upon a sound hypothesis for implantation, and where careful attention is paid to surface EEG in guiding implantation.
- Epileptogenic zone was studied in 28 patients. The most frequent location of the epileptogenic zone was the frontal lobe. The most frequent pathological findings were focal cortical dysplasia (FCD) in 21 patients. Most of them were FCD ILAE type II.

ObjectiveThe aim of this study is to determine outcome of resective epilepsy surgery in MRI-negative extratemporal lobe epilepsy (MNETLE) patients who underwent invasive evaluations and to determine factors governing outcome.MethodsWe studied 28 patients who underwent resective epilepsy surgery for MNETLE from August 2006 to November 2015, in whom complete follow-up information was available. Electro-clinical, pathological and surgical data were evaluated. 24 patients (82.8%) were explored with intracranial EEG (9 stereoelectroencephalography (SEEG), 7 subdural grids and 8 both). All patients were followed for at least 6 months.ResultsDuring a mean follow up period of 32 [6-113] months, 13 (46.4%) patients became seizure-free (ILAE 1) and 18 (64.3%) had a good (ILAE 1, 2, 3) outcome. 21 (75.0%) patients had focal cortical dysplasia (FCD). Univariate analysis showed that more restricted (regional) interictal and ictal epileptiform discharges in surface EEG were significantly associated with seizure freedom (P = 0.016 and P = 0.024). Multivariate analysis confirmed that having ≥120 electrode contacts in the evaluation is an independent variable predicting seizure freedom (HR = 4.283, 95% CI = 1.342-13.676, P = 0.014).ConclusionInvasive EEG is a powerful tool in the pre-surgical evaluation of patients with MNETLE. Invasive EEG implantation that include the irritative zone and EEG onset zone as indicated by surface EEG, as well as wider brain coverage predict seizure freedom, contingent upon a sound anatomo-electro-clinical hypothesis for implantation.