title: Bilateral intracranial electrodes for lateralizing intractable epilepsy: efficacy, risk, and outcome.
abstract: OBJECTIVE
  Medically refractory epilepsy is amenable to neurosurgical intervention if the epileptogenic focus is accurately localized. If the scalp video-electroencephalography (EEG) and magnetic resonance imaging are nonlateralizing, yet a single focus is suspected, video-EEG monitoring with bilateral intracranial electrode placement is helpful to lateralize the ictal onset zone. We describe the indications, risks, and utility of such bilateral surveys at our institution.
  
  
  METHODS
  We retrospectively reviewed 26 patients with medically refractory seizures who were treated over a 5-year period and underwent bilateral placement of intracranial electrodes. Subdural strips were used in all cases, and additional stereotactic implantation of depth electrodes into mesial temporal lobes occurred in 50%. The mean patient age was 37.7 years, and 65.4% of patients were male.
  
  
  RESULTS
  The most common indication for bilateral invasive monitoring was bilateral ictal onsets on surface video-EEG (76.9%), followed by frequent interictal spikes contralateral to a single ictal focus (7.7%). Intracranial monitoring lasted an average of 8.2 days, with ictal events recorded in all cases. Ten patients (38.5%) subsequently underwent more extensive unilateral monitoring via implantation of subdural and depth electrodes through a craniotomy. A therapeutic procedure was performed in 17 patients (65.4%), whereas 1 patient underwent a palliative corpus callosotomy (3.8%). Nine patients underwent a resection without unilateral invasive mapping. Reasons for no therapeutic surgery (n = 8) included multifocal onsets, failing the Wada test, refusal of further treatment, and negative intraoperative electrocorticogram. There was 1 surgical complication, involving a retained electrode fragment that was removed in a separate minor procedure. Of the 26 patients, 15 (57.7%) are now seizure-free or have seizure disorders that have substantially improved (modified Engel classes I and II). Of the 17 patients who underwent a potentially curative surgery, 13 (76.5%) were Engel classes I and II.
  
  
  CONCLUSIONS
  Bilateral placement of subdural strip and depth electrodes for epilepsy monitoring in patients with nonlateralizing scalp EEG and/or discordant imaging studies but clinical suspicion for focal seizure origin is both safe and effective. Given the safety and efficacy of this procedure, epileptologists should have a low threshold to consider bilateral implants for suitable patients.
authors.affiliation: Department of Neurological Surgery, Weill Cornell Medical College, New York-Presbyterian Hospital, New York, New York 10065, USA.
authors.forename: Dimitris G
authors.initials: DG
authors.lastname: Placantonakis
authors.forename: Saadat
authors.initials: S
authors.lastname: Shariff
authors.forename: Fabien
authors.initials: F
authors.lastname: Lafaille
authors.forename: Douglas
authors.initials: D
authors.lastname: Labar
authors.forename: Cynthia
authors.initials: C
authors.lastname: Harden
authors.forename: Syed
authors.initials: S
authors.lastname: Hosain
authors.forename: Padmaja
authors.initials: P
authors.lastname: Kandula
authors.forename: Neil
authors.initials: N
authors.lastname: Schaul
authors.forename: Dimitrius
authors.initials: D
authors.lastname: Kolesnik
authors.forename: Theodore H
authors.initials: TH
authors.lastname: Schwartz
mesh_terms: D000328:Adult; D003399:Craniotomy / Q000379:methods; D046690:Deep Brain Stimulation / Q000379:methods*; D004567:Electrodes, Implanted; D004569:Electroencephalography / Q000379:methods; D004827:Epilepsy / Q000503:physiopathology / Q000628:therapy*; D005260:Female; D007839:Functional Laterality / Q000502:physiology*; D006801:Humans; D008137:Longitudinal Studies; D008279:Magnetic Resonance Imaging; D008297:Male; D008991:Monitoring, Physiologic; D011612:Psychosurgery; D012189:Retrospective Studies; D013702:Temporal Lobe / Q000502:physiology; D015898:Tomography Scanners, X-Ray Computed; D016896:Treatment Outcome; D014743:Videotape Recording