Abstracts

Rationale: Patients with pharmacotherapy-resistant focal epilepsy may be candidates for surgical intervention if the seizure onset zone can be well localized. In patients with seizures suspected to arise near prior surgical resections, it can be technically challenging and potentially dangerous to implant subdural strip and grid electrodes. Stereoelectroencephalography (SEEG) offers potential advantages, but there is limited data on safety and efficacy in this difficult cohort. Methods: We review our initial 2-year consecutive experience with SEEG in patients with prior surgery (resection or ablation) and focal epilepsy between July 2014 and June 2016. We assess SEEG coverage and localization, seizure outcomes following subsequent surgical treatments, and SEEG complications. Results: Thirteen patients with medically refractory epilepsy and prior surgical interventions underwent SEEG. Median age was 20 years (range 12-51). Twelve patients had prior craniotomies for resections and 1 had an extra-temporal (ET) laser ablation. Eleven patients had epilepsy prior to their initial procedure: 4 with suspected focal cortical dysplasia, 2 with nonlesional epilepsy, 2 tumors, 1 mesial temporal sclerosis, 1 Rasmussen’s encephalitis, and 1 cavernous malformation. Two patients with resections following a gunshot wound and a ruptured arteriovenous malformation developed epilepsy after their initial surgeries. Five surgical cavities were temporal, 5 ET, and 3 spanned temporal and ET territory.Based on pre-implantation hypotheses, all SEEG investigations covered areas adjacent and deep to the procedural cavities. All arrays included ET coverage and 10 also included a temporo-limbic investigation. Two patients also received contralateral electrodes.The seizure onset zone was localized to a single focus in 9 patients. The focus was adjacent to the procedural cavity in 8 patients and remote in 1. Eight patients underwent further tailored resections (4 temporal and 4 ET) and 1 deferred due to the involvement of eloquent cortex. At last follow-up (median 10 months, reported range 1.5-30.8), 5 patients were free of disabling seizures (Engel I), 2 had improvement (Engel II or III), and 1 was less than a month from surgery.Three patients had multifocal onsets. One had unilateral multifocal onset surrounding the prior resection cavity and underwent functional hemispherectomy. One had two distinct foci on opposing aspects of the cavity but declined further surgical intervention. One had bilateral multifocal onset and is considering a palliative stimulation procedure. In the final patient the evaluation did not reveal a clear localization and she is considering palliative stimulation or repeat SEEG.There were no major SEEG complications such as intracerebral hemorrhage, intracranial infection, or new neurologic deficit. One patient had a single electrode site treated for superficial infection at the time of explant. Conclusions: SEEG is a safe and efficacious technique for localizing seizure onsets relative to prior surgical areas. SEEG permits deep, three-dimensional, and multi-lobar investigations surrounding cavities, while avoiding large, re-operative craniotomies. Funding: The Columbia Comprehensive Epilepsy Center Epilepsy Surgery Database is supported by the Henry Lapham Memorial Award from Citizens United for Research in Epilepsy (CURE) to Dr. Bateman and Dr. Schevon.*Dr. Feldstein and Dr. McKhann share senior authorship for this work.