New epilepsy surgical techniques and intraoperative monitoring in non-lesional MRI negative epilepsy

Abstract

Progress in neurosurgical techniques in epilepsy surgery for non-lesional (NL) MRI negative and drug-refractive epilepsy, especially extratemporally located epilepsy, has significantly enhanced the postoperative seizure freedom rates of children, adolescents and adults. For the presurgical evaluation of NL epilepsies in most of the cases invasive monitoring is a prerequisite to confirm the focal nature of the epilepsy and to define a putative epileptogenic zone for surgical resection or ablation. The technique of invasive monitoring has significantly changed during the last decade, using more often minimally invasive depth electrodes (stereo-EEG) instead of subdural electrodes with large craniotomies. Depth electrodes have the advantage of monitoring deep seizure foci as well as reconstruction of 3‑D epileptogenic volumes as a putative target for resection or ablation. This strategy may be enhanced in the future by using artificial intelligence (AI) and goes along with significantly less perioperative complications; however, considering monitoring and mapping of speech relevant cortical areas, subdural electrode implantation is still without an alternative. Additionally, new techniques in neurosurgery, such as neuronavigation (image guided surgery, IGS), intraoperative MRI, intraoperative neuromonitoring and electrocorticography and robotic as well as laser ablation are able to spare highly eloquent brain areas during access and resection/ablation; however, traditional techniques, such as intraoperative electrocorticography (ECoG) and intraoperative neuromonitoring (IONM), compliment data for image-guided surgery during operations using microscopical image guidance. These developments enable us to perform surgery in significantly more and more complicated NL epilepsy patients with the result of a better postoperative seizure freedom rate.