DEPTH ELECTRODE STUDIES IN TEMPORAL-LOBE EPILEPSY - RELATION TO QUANTITATIVE MAGNETIC-RESONANCE-IMAGING AND OPERATIVE OUTCOME

We performed a retrospective study of 30 patients with presumed intrac table temporal lobe epilepsy (TLE) who underwent chronic intracranial EEG monitoring (CIEM). Multicontact depth electrodes were stereotactic ally implanted through the medial occipital lobe into amygdala and hip pocampus. All patients had previously undergone extracranial ictal EEG monitoring that proved inadequate to localize the epileptogenic zone. No morbidity was associated with CIEM in the 30 patients. Twenty-five patients were shown to have exclusively or predominantly unilateral t emporal lobe seizures, and 5 patients had bitemporal seizures without unilateral predominance; 24 patients subsequently underwent an anterot emporal lobe cortical resection. Twenty-one patients have been followe d a minimum of 1 year postoperatively. Nine patients (43%) had a class I outcome (seizure-free, auras only, or provoked seizures), 3 patient s (14%) had a class II outcome (greater than or equal to 95% seizure r eduction), 4 patients (19%) had a class III outcome (greater than or e qual to 50% seizure reduction); and 5 patients (24%) had a class IV ou tcome (<50% seizure reduction or no change). A prolonged interhemisphe ric propagation time (p < 0.01) and magnetic resonance imaging (MRI)-i dentified hippocampal atrophy (p < 0.01) correlated with a favorable s urgical outcome. Results of this study may prove useful in counseling patients who undergo CIEM before temporal lobe surgery.