Noninvasive correlates of subdural grid electrographic outcome

Area of Science:

• Epilepsy research
• Neurosurgery
• Clinical electroencephalography

Background:

• Subdural grid evaluation (SDE) is an invasive method to localize seizure foci.
• Identifying surgical candidates for epilepsy surgery requires accurate localization.
• Nonlesional MRI presents challenges in pre-surgical evaluation.

Purpose of the Study:

• To determine reasons why patients do not undergo resective epilepsy surgery after SDE.
• To correlate noninvasive investigation results with invasive EEG findings in patients with nonlesional MRIs.

Main Methods:

• Retrospective analysis of 140 adult epilepsy patients undergoing SDE over 8 years.
• Development of semiquantitative scores and Bayesian predictors for noninvasive data.
• Analysis of concordance between noninvasive and invasive EEG in nonlesional MRI cases.

Main Results:

• 25 of 140 patients were denied surgery, primarily due to nonlocalizing subdural ictal EEG onset (10 patients).
• Most patients denied surgery (8/10) had nonlesional MRIs.
• Noninvasive parameters, especially concordant scalp interictal EEG, predicted focal invasive EEG findings using Bayesian analysis.

Conclusions:

• Nonlocalizing intracranial EEG is a significant reason for denying epilepsy surgery post-SDE.
• The majority of these patients have nonlesional MRIs.
• Semiquantitative scores and Bayesian likelihood ratios derived from noninvasive data can aid in selecting and counseling epilepsy surgery candidates.