Abstracts

Rationale: Investigating insular epilepsy with invasive techniques poses many unique challenges.  Surface electrode recordings are seldom able to capture insular electrical activity.  Insular monitoring with depth electrodes has historically been performed using orthogonal transopercular trajectories, which limit the number of contacts able to access the insular cortex.  It is suggested that oblique insular trajectories utilizing stereoelectroencephalography (SEEG) may provide a more robust picture of insular activity due to the increased number of cortical electrode contacts within the insular cortex.  Unfortunately, there is a dearth of data regarding the safety, diagnostic yield, and clinical utility of oblique insular trajectories in SEEG. Methods: The charts of all patients who underwent placement of insular SEEG electrodes at our institution were reviewed.  Electrode trajectories were planned preoperatively using MRI data co-registered with flat-detector computer tomography (FD-CT) scans performed with concurrent cerebral angiography for vessel imaging.  Electrodes were implanted along planned trajectories with the use of a CRW frame or robotic assistance, and insular electrodes were placed using our previously described insular triangulation technique.  All patients underwent postoperative imaging with CT and/or MRI to evaluate for possible complications and were subsequently monitored in a dedicated epilepsy monitoring unit.  Data from patients who exhibited insular spread of electrical activity are presented. Results: A total of 46 patients underwent SEEG implantation at our institution during the study period.  Insular electrodes were placed as part of an overall implant scheme in 26 (56.5%) patients.  A total of 71 electrodes were placed with 1114 total contacts.  There were no clinically significant complications related to the implant procedure.  All insular electrodes were placed along oblique trajectories.  In patients with insular electrodes placed, there were 6 (23.1%) patients with 1 electrode placed, 2 (7.7%) with 2 electrodes, 12 (46.2%) with 3 electrodes, 4 (19.2%) with 4 electrodes and 1 (3.8%) with 5 electrodes (Median=3, Mean=2.7).  Insular involvement was detected in 18 (69.2%) patients, with at least 29 (40.8%) electrodes picking up insular activity.  Insular onset was seen in 9 (34.6%) patients, insular spread in 6 (23.1%) patients and indeterminate insular involvement in 3 (11.5%) patients.  A total of 22 (84.6%) implanted patients underwent surgical resection, with 10 patients (38.5% overall, 55.6% with insular involvement) undergoing insulectomy as either their primary resection focus or as part of an extended extra-insular resection. Conclusions: Placing multiple insular SEEG electrodes can safely identify insular epileptogenic activity and effectively guide surgical decision making.  Oblique insular trajectories should be considered in patients with suspected insular involvement to maximize the potential yield of SEEG recordings. Funding: None