Depth Electrode Studies in Temporal Lobe Epilepsy: Relation to Quantitative Magnetic Resonance Imaging and Operative Outcome

Summary: We performed a retrospective study of 30 patients with presumed intractable temporal lobe epilepsy (TLE) who underwent chronic intracranial EEG monitoring (CIEM). Multicontact depth electrodes were stereotactically implanted through the medial occipital lobe into amygdala and hippocampus. All patients had previously undergone extracranial ictal EEG monitoring that proved inadequate to localize the epileptogenic zone. No morbidity as associated with CIEM in the 30 patients. Twenty-five patients were shown to have exclusively or predominantly unilateral temporal lobe seizures, and 5 patients had bitemporal seizures without unilateral predominance; 24 patients subsequently underwent an anterotemporal lobe cortical resection. Twenty-one patients have been followed a minimum of 1 year postoperatively. Nine patients (43%) had a class I outcome (seizure-free, auras only, or provoked seizures), 3 patients (14%) had a class I1 outcome (≥95% seizure reduction), 4 patients (19%) had a class III outcome (≥50% seizure reduction); and 5 patients (24%) had a class IV outcome (<50% seizure reduction or no change). A prolonged interhemispheric propagation time (p <0.01) and magnetic resonance imaging (MR1)-identified hippocampal atrophy (p <0.01) correlated with a favorable surgical outcome. Results of this study may prove useful in counseling patients who undergo CIEM before temporal lobe surgery.