Using pre-surgical suspicion to guide insula implantation strategy

Area of Science:

• Neurosurgery
• Epileptology
• Neurophysiology

Background:

• Insular epilepsy diagnosis is challenging due to overlapping semiology and scalp EEG findings.
• Stereotactic electroencephalography (sEEG) offers improved seizure onset localization but carries implantation risks in the vascularly rich insula.

Purpose of the Study:

• To review the safety and pre-implantation factors for insular electrode placement in patients undergoing invasive epilepsy monitoring.
• To evaluate the predictive value of presurgical findings for insular seizure onset.

Main Methods:

• Retrospective review of 79 surgical cases (2016-2019) involving insular electrode placement for invasive epilepsy monitoring.
• Analysis of presurgical data, operative reports, and invasive EEG summaries to identify insular involvement.
• Categorization of pre-sEEG insular onset suspicion based on MRI, PET/SPECT/scalp EEG, semiology, or prior treatment history.

Main Results:

• Seven patients (8.9%) demonstrated insular ictal onset among 76 patients who received 189 insular electrodes.
• One significant complication (left hemiparesis) occurred in a moderate suspicion case.
• The likelihood of insular ictal onset increased with suspicion level: 5.3% (low), 8.6% (moderate), and 40% (high).

Conclusions:

• Insular electrode placement via sEEG is safe and feasible for epilepsy monitoring.
• Two or more presurgical indicators strongly predict insular seizure onset, aiding in targeted invasive monitoring.
• Pre-implantation clinical findings provide predictive value for guiding insular targeting in invasive EEG evaluations.