Introduction: Intra-cranial EEG monitoring of presumed insular lobe epilepsy is technically challenging. Previously reported strategies of trans-sylvian depth electrode placement and trans-opercular stereo EEG (SEEG) trajectories risk injury to the middle cerebral artery branches. We describe a technique for long-axis SEEG cannulation along the triangular boundaries of the insular cortex. In patients with demonstrated insular lobe onset, electrodes were left in-situ to guide the boundaries of resection

Methods: As part of larger implants for seizure onset localization, 14 patients were implanted with insular SEEG electrodes using the triangulation technique with robotic assistance. Three electrodes comprise the triangulation technique, approximating the cortex along the sylvian triangle, lying within grey matter deep to the superior, inferior, and anterior circular sulci. Long-axis cannulation allowed electrodes to be left in place to guide resection without interfering with the cranial flap.

Results: Technical success was achieved in all insular SEEG implantations, with an average of 7.1 active insular contacts per electrode (range 5-9). There were no procedural complications related to electrode placement, including no incidences of intracranial hemorrhage. In five patients, insular onset was discovered, resulting in tailored insulectomy performed by trans-opercular, sub-pial resection. In three patients, anterior-inferior quadrant insulectomy was performed, anterior insulectomy in one patient, and complete insulectomy in one patient. One patient experienced worsening of baseline hemiparesis. There were no other peri-operative complications. At short-term follow up (range 3-6 months0, four patients achieved Engel Class 1A seizure freedom, while the third has Engel Class 1B outcome with persistent epigastric aura.

Conclusions: The insular triangulation technique allows broad investigation of the insula, spanning functional subdivisions of the insular lobe, and permits tailored partial insulectomy.

Patient Care: This technique represents a significant improvement in the techniques for intra-cranial EEG recording for presumed insular epilepsy, as well as a key improvement in guiding the necessary extent of insular resection.

Learning Objectives: By the conclusion of this session, participants should be able to describe the novel SEEG technique for insular lobe recording, as well as the use of SEEG electrodes for guidance of insular resection.

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