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Rei Enatsu, Jorge Gonzalez-Martinez, Juan Bulacio, John C. Mosher, Richard C. Burgess, Imad Najm, and Dileep R. Nair

OBJECT

The frontal and insular fiber network in humans remains largely unknown. This study investigated the connectivity of the frontal and anterior insular network in humans using cortico-cortical evoked potential (CCEP).

METHODS

This retrospective analysis included 18 patients with medically intractable focal epilepsy who underwent stereoelectroencephalography and CCEP. Alternating 1-Hz electrical stimuli were delivered to parts of the frontal lobe and anterior insula (prefrontal cortex [PFC], ventrolateral and dorsolateral premotor area [vPM and dPM, respectively], presupplementary motor area [pre-SMA], SMA, frontal operculum, and anterior insula). A total of 40–60 stimuli were averaged in each trial to obtain CCEP responses. The distribution of CCEP was evaluated by calculating the root mean square of CCEP responses.

RESULTS

Stimulation of the PFC elicited prominent CCEP responses in the medial PFC and PMs over the ipsilateral hemisphere. Stimulation of the vPM and dPM induced CCEP responses in the ipsilateral frontoparietal areas. Stimulation of the pre-SMA induced CCEP responses in the ipsilateral medial and lateral frontal areas and contralateral pre-SMA, whereas stimulation of the SMA induced CCEP responses in the bilateral frontoparietal areas. Stimulation of the frontal operculum induced CCEP responses in the ipsilateral insula and temporal operculum. CCEPs were observed in the ipsilateral medial, lateral frontal, and frontotemporal operculum in the anterior insular stimulation. Stimulation of the vPM and SMA led to the network in the dominant hemisphere being more developed.

CONCLUSIONS

Various regions within the frontal lobe and anterior insula were linked to specific ipsilateral and contralateral regions, which may reflect distinct functional roles.

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Juan C. Bulacio, James Bena, Piradee Suwanpakdee, Dileep Nair, Ajay Gupta, Andreas Alexopoulos, William Bingaman, and Imad Najm

OBJECTIVE

The aim of this study was to investigate seizure outcomes after resective epilepsy surgery following stereoelectroencephalography (SEEG), including group characteristics, comparing surgical and nonsurgical groups and assess predictors of time to seizure recurrence.

METHODS

Clinical and EEG data of 536 consecutive patients who underwent SEEG at Cleveland Clinic Epilepsy Center between 2009 and 2017 were reviewed. The primary outcome was defined as complete seizure freedom since the resective surgery, discounting any auras or seizures that occurred within the 1st postoperative week. In addition, the rate of seizure freedom based on Engel classification was determined in patients with follow-up of ≥ 1 year. Presumably significant outcome variables were first identified using univariate analysis, and Cox proportional hazards modeling was used to identify outcome predictors.

RESULTS

Of 527 patients satisfying study criteria, 341 underwent resective surgery. Complete and continuous seizure freedom after surgery was achieved in 55.5% of patients at 1 year postoperatively, 44% of patients at 3 years, and 39% of patients at 5 years. As a secondary outcome point, 58% of patients achieved Engel class I seizure outcome for at least 1 year at last follow-up. Among surgical outcome predictors, in multivariate model analysis, the seizure recurrence rate by type of resection (p = 0.039) remained statistically significant, with the lowest risk of recurrence occurring after frontal and temporal lobe resections compared with multilobar and posterior quadrant surgeries. Patients with a history of previous resection (p = 0.006) and bilateral implantations (p = 0.023) were more likely to have seizure recurrence. The absence of an MRI abnormality prior to resective surgery did not significantly affect seizure outcome in this cohort.

CONCLUSIONS

This large, single-center series shows that resective surgery leads to continuous seizure freedom in a group of patients with complex and severe pharmacoresistant epilepsy after SEEG evaluation. In addition, up to 58% of patients achieved seizure freedom at last follow-up. The authors’ results suggest that SEEG is equally effective in patients with frontal and temporal lobe epilepsy with or without MRI identified lesions.