Subdural Strip Electrode Studies in Temporal Lobe Epilepsy: Relation between Interhemispheric Propagation Time and Surgical Outcome

ABSTRACT

BACKGROUND: We evaluated whether the time required for a seizure to spread contralaterally, interhemispheric propagation time (IHSPT) could be related to post-surgical outcome in temporal lobectomy. METHODS: We performed a retrospective study of 28 patients. All patients had previously undergone a phase I presurgical evaluation including MRI and video-EEG monitoring with scalp and sphenoidal electrodes, which strongly suggested the diagnosis of mesial temporal lobe epilepsy, but proved inadequate to lateralize the epileptogenic zone. All patients performed the video-EEG monitoring with bilateral subdural strip electrodes on their basal and mesial temporal area and unilateral temporal lobectomy with a minimum of 1-year follow up postoperatively. IHSPT was divided into two categories, 0~5.0 seconds, 5.1 seconds or longer. RESULTS: Sixteen patients (57.1%) were seizure free and 12 suffered persistent seizures. A prolonged IHSPT (> 5.0sec) significantly correlated with a favorable surgical outcome (P = 0.05). Hippocampal atrophy on MRI significantly correlated with prolonged IHSPT (P<0.05). CONCLUSIONS: Our result suggests that hippocampal atrophy on MRI and IHSPT can predict the surgical outcome and may be used as the selection criteria of temporal lobectomy for patients with intractable temporal lobe epilepsy.