Abstracts

Rationale: The RNS System (NeuroPace, Inc.) provides closed loop direct brain-responsive neurostimulation for treatment of medication-resistant focal epilepsy. Chronic ambulatory electrocorticography (ECoG) can provide information about lateralization of mesial temporal lobe (MTL) seizures to help identify patients who could benefit from MTL ablative or resective procedures^1,2. Many centers utilize a longitudinal (trans-occipital) approach for MTL depth lead placement in an attempt to cover the length of the hippocampus, though some centers use an orthogonal (lateral) approach³. We present a case during which replacement of orthogonal with longitudinal MTL depth leads altered the side from which the patient’s intracranial epileptiform activity was typically recorded.

Methods: The patient was treated with the RNS System and bilateral orthogonally-placed MTL depth leads that were later switched to bilateral longitudinally-placed MTL depth leads. Data were retrospectively reviewed. ECoG data was reviewed online via the Patient Data Management System.

Results: A 48-year-old right-handed man presented to an outside facility with a 21-year history of medication-resistant epilepsy. Most seizures were focal impaired awareness seizures characterized by staring with speech arrest, manual automatisms, and sometimes, posturing of either arm. Seizures occurred once or twice per week with occasional focal to bilateral tonic clonic seizures. The MRI was non-lesional and video EEG showed bitemporal independent spikes and 12 typical electro-clinical seizures split in onset between the bilateral temporal regions. The patient was further evaluated with bitemporal stereo EEG that recorded typical bilateral independent MTL onset seizures. The patient was implanted with the RNS neurostimulator and bilateral orthogonally placed MTL depth leads (total contact span 13.6mm), targeting mesial temporal structures. During the initial two years of RNS System ECoG recording, 81% of the detections were recorded from the right MTL and 19% originated from the left MTL. A right temporal lobectomy was discussed with the patient but declined. The patient presented to our center and their data was reviewed at our multidisciplinary epilepsy conference. The bilateral orthogonal MTL depth leads were replaced with bilateral longitudinal MTL leads (total contact span 33.1mm) to monitor and treat the length of the hippocampi, versus the more limited area covered by the orthogonal placement. In contrast to prior results, 11 months of recording showed that 94% of detections were left MTL compared to 6% from the right MTL. The patient continues to have focal impaired awareness seizures once or twice per week but overall reports 1-25% improvement since prior to RNS System implantation.

Conclusions: In this case study, longitudinal MTL depth lead placement provided improved coverage of mesial temporal structures and may provide more accurate information for seizure localization.

1. King‐Stephens D, et al. Epilepsia. 2015;56(6):959–67.
2. Hirsch LJ, et al. Epilepsia. 2020;61
3. E.B. Geller, et al. Epilepsia, 58 (2017), pp. 994-1004
4. Horn A, Kuhn AA. Neuroimage. 2015;107:127-35

Funding: Please list any funding that was received in support of this abstract.: None.