Scalp and Intracranial EEG in Medically Intractable Extratemporal Epilepsy with Normal MRI

Abstract

.Purpose. To investigate EEG and SPECT in the surgical outcome of patients with normal MRI (nonlesional) and extratemporal lobe epilepsy. Methods. We retrospectively identified 41 consecutive patients with nonlesional extratemporal epilepsy who underwent epilepsy surgery between 1997 and 2007. The history, noninvasive diagnostic studies (scalp EEG, MRI, and SPECT) and intracranial EEG (iEEG) monitoring was reviewed. Scalp and iEEG ictal onset patterns were defined. The association of preoperative studies and postoperative seizure freedom was analyzed using Kaplan-Meier analysis, log-rank test, and Cox proportional hazard. Results. Thirty-six of 41 patients had adequate information with a minimum of 1-year followup. Favorable surgical outcome was identified in 49% of patients at 1 year, and 35% at 4-year. On scalp EEG, an ictal onset pattern consisting of focal beta-frequency discharge (>13-125 Hz) was associated with favorable surgical outcome (P = 0.02). Similarly, a focal fast-frequency oscillation (>13-125 Hz) on iEEG at ictal onset was associated with favorable outcome (P = 0.03). Discussion. A focal fast-frequency discharge at ictal onset identifies nonlesional MRI, extratemporal epilepsy patients likely to have a favorable outcome after resective epilepsy surgery.

Linking MRI postprocessing with magnetic source imaging in MRI‐negative epilepsy

“…The shortcomings of scalp EEG in the presurgical investigations of MRI– epilepsy patients have been well recognized in the literature. 52, 53 Despite its own shortcomings related to cost, and brevity of recording, MEG has better localization abilities as compared to scalp EEG, in part due to a combination of simpler source modeling parameters 54 and more sensor coverage. For these reasons, in this study we utilized MSI to provide noninvasive electrophysiological confirmation of epileptogenicity at the sublobar level when MAP indicates a possible region of concern.…”

The pathology of magnetic-resonance-imaging-negative epilepsy

“…4 At present, surgical management of MRInegative pharmacoresistant focal epilepsy patients relies heavily on invasive intracranial electroencephalography, which is based on complimentary review of other noninvasive modalities including positron emission tomography, ictal single-photon emission computed tomography, and magnetoencephalography when available. [5][6][7][8] Despite substantial efforts, the lack of a lesion on MRI has consistently been shown to be one of the predictors for surgical failure. 9,10 Therefore, MRI-negative patients are usually considered unfavorable surgical candidates 4 and are often denied epilepsy surgery.…”

Comparing the effects of cortical resection and vagus nerve stimulation in patients with nonlesional extratemporal epilepsy

“…Engel I + II outcome in RESgr was reached in 46.2% and 47.3% at the 2-and 5-year follow-up visits, respectively. The rate of excellent postoperative outcomes (Engel I) after resective surgery for NLexTLE varies substantially in the literature (from 25 to 50%) [13,[16][17][18][19][20][21]. This significant diversity is obviously influenced by several factors, including the era in which the study was conducted because of developments and innovations in preoperative diagnostic methods including MRI and functional neuroimaging and also including the experience and strategies of each epilepsy center in managing patients with NLexTLE.…”

“…The localization of the SOZ using either noninvasive or invasive preoperative evaluation is the most complicated in patients with "nonlesional" exTLE (NLexTLE), and, therefore, their seizure outcome is the worst among patients with refractory epilepsy. The percentage of seizure-free patients with NLexTLE in the literature varies from 25 to 50% [13,[16][17][18][19][20][21].…”