Abstracts

Medically refractory epilepsy is amenable to neurosurgical intervention if the epileptogenic focus can be accurately localized. In some situations, the scalp EEG and MRI are discordant and/or non-lateralizing, yet the clinician is still highly suspicious that a single focus exists, either based on a dominant interictal focus or stereotypical semiology. In these situations, a bilateral intracranial survey can be helpful to lateralize the ictal onset zone. The risks and success of such bilateral surveys have not been well described., We retrospectively reviewed 20 patients with refractory seizures treated over a 4-year period. Patients underwent bilateral placement of subdural strip electrodes and, in 50% of cases, stereotactic implantation of depth electrodes into the mesial temporal lobes. In all cases the MRI scans and scalp EEG were not sufficiently concordant to lateralize seizure onsets. The mean age was 35.1 years and 75% of patients were male., Patients were electrophysiologically monitored for an average of 7.4 days. Thirty-five percent (n=7) subsequently underwent unilateral implantation of electrodes to more accurately localize the seizure focus. Sixty percent (n=12) eventually underwent a therapeutic procedure. Of those, 58.3% underwent resection of epileptogenic foci without unilateral invasive mapping. Reasons for no further surgery (n=8) included failing the WADA (37.5%), multifocal onsets (25%), refusal of further treatment (12.5%) and negative intraoperative ECoG (12.5%). There was 1 complication, involving a retained electrode fragment that was removed in a separate minor procedure. Of the surgically treated patients, 58.3% have no seizures currently, 16.7% have improved and 25% remain unchanged., Bilateral placement of subdural strip and depth electrodes to survey the cortex in patients with non-lateralizing scalp video-EEG and MRI but clinical suspicion for localized epilepsy is both safe and effective. Of those patients who go on to a therapeutic procedure, 75% are either improved or seizure-free.,