Authors :
Nathaniel Cameron, BA – University of Kansas Medical Center; Lane Fry, BA – Neurosurgery – University of Kansas Medical Center; Jean-Luc Kabangu, MD – Neurosurgery – University of Kansas Medical Center; Brian Schatmeyer, MD – Neurosurgery – University of Kansas Medical Center; Christopher Miller, MD – Neurosurgery – Thomas Jefferson School of Medicine; Carol Ulloa, MD – Neurology – University of Kansas Medical Center; Utku Uysal, MD, MS – Neurology – University of Kansas Medical Center; Jennifer Cheng, MD, MS – Neurosurgery – University of Kansas Medical Center; Michael Kinsman, MD – Neurosurgery – University of Kansas Medical Center; Adam Rouse, MD, PhD – Neurosurgery – University of Kansas Medical Center; Patrick Landazuri, MD – Neurology – University of Kansas Medical Center
Rationale: Insula epilepsy can be a challenging diagnosis due to overlapping semiology and scalp EEG findings with frontal, temporal, and parietal lobe epilepsies. Stereotactic electroencephalography (sEEG) provides an opportunity to better localize seizure onset. The possibility of improved localization is balanced by implantation risk in this vascularly rich region. We review both safety and pre-implantation factors involved in insula electrode placement across four years at the University of Kansas Medical Center (KUMC).
Methods: Presurgical data, operative reports, and invasive EEG summaries were retrospectively reviewed for KUMC patients undergoing intracranial EEG monitoring from 2016 to 2019. Patients receiving at least one insula targeting electrode were reviewed. The patient’s epileptologist verified the collected data and categorized insula intracranial involvement as one of five options: ictal onset, first spread, second spread, interictal abnormalities only, or none of the above. Lastly, the epileptologist indicated which presurgical clinical, imaging, or EEG finding(s) suggested need for insula electrode implantation. The likelihood of pre-sEEG insula onset was categorized as “low suspicion” if insula contacts were included as rule out only, “moderate suspicion” if one finding was present before surgery, and “high suspicion” if two or more findings were present.
Results: In the 153 consecutive patients implanted from 2016-2019, 75 patients (61%) received 190 insula electrodes as part of their implantation strategy. The average age at the time of surgery was 37.9 years. _x000D_
Eight patients (10.6%) had insula ictal onset. Temporal lobe (48 cases, 64%) was the most common seizure onset. For 18 temporal onset cases (37.5%), the insula was the first site of ictal spread. Twenty-five patients (33.3%) had no defined insula involvement. One clinically significant complication (left hemiparesis) occurred in a patient with moderate suspicion for insula onset. This was a superior trajectory targeting the right posterior insula resulting in a frontal intraparenchymal hemorrhage. The resulting clinically significant complication rate per electrode was 0.53%. There were 38 low suspicion cases, 35 moderate suspicion cases, and 6 high suspicion cases for pre-sEEG insula ictal onset. Two low
suspicion (5.3%), three moderate
suspicion (8.6%), and three high suspicion (50%) cases had insular ictal onset.
Conclusions: Stereotactic placement of insular depth electrodes is safe. Having more than one presurgical factor indicating insular onset is a strong, albeit incomplete, predictor of insular seizure onset. Conversely, having one or less presurgical factor indicating insular onset conveys a far lower likelihood of insular seizure onset. Using pre-implantation clinical findings can help risk stratify insular electrode placement decisions.
Funding: Kansas University Training Program in Neurological and Rehabilitation Sciences (NIH T32 award) was supported by NIH Award Number T32HD057850.