Abstracts

Presurgical evaluation of patients with suspected temporal lobe epilepsy often requires Phase II (intracranial) video-EEG monitoring, particularly when noninvasive Phase I (extracranial) recordings are not localizing, and there is no lesion on magnetic resonance imaging (MRI). Foramen ovale electrodes (FOEs) are less invasive than conventional intracranial electrodes, and provide unique data of mesial temporal seizure onset and propagation pattern, propagation time, and duration of discharge. This study compared the ictal recordings from FOEs in epilepsy surgery patients at a single center with or without MRI evidence of mesial temporal sclerosis (MTS). Seizure-free surgery patients with MRI evidence of MTS served as the gold standard for mesial temporal patterns of seizure onset and spread against which the nonlesional group was compared.
We retrospectively reviewed 74 patients with medically refractory complex partial seizures and suspected temporal lobe epilepsy that were evaluated presurgically with 3 to 5 contact FOEs at UCSD. Two groups of patients were selected for further analysis: 1) patients (n=20) without evidence of MTS or any other lesion on MRI and 2) patients (n=11) with MRI evidence of MTS that remained seizure-free after tailored temporal resection. All surgical patients had a follow up of at least two years (range 2-11 yrs, mean 7.4 yrs). FOE-recorded seizures were analyzed for pattern of discharge at seizure onset, duration at primary epileptogenic foci, pattern of discharge propagation to scalp and contralateral FOEs, and seizure duration.
Of the 20 nonlesional patients, FOE recordings excluded 11 from consideration of tailored temporal lobectomy (bilateral seizure onsets in five, seizure onset not localized to FOEs in six). Of the remaining nine patients determined to be surgical candidates by FOE recordings, one declined surgery and eight underwent tailored temporal lobectomy.
No consistent differences in patterns of discharge at seizure onset, duration at primary epileptogenic foci, pattern of discharge propagation, and seizure duration were found between the non-MTS patients that were offered surgery and the seizure-free MTS group (Engel Class I by design). Surgical outcome of patients without MTS was Class I in 6 patients, Class II in one patient, and class III in one patient.
FOEs provide reliable localizing information for indication of surgical treatment of nonlesional temporal lobe epilepsy. With minimal invasiveness, FOEs readily identifies patients with bilateral independent seizure foci and patients without mesial temporal seizure onset or propagation. Nonlesional patients with FOE seizure patterns resembling those of patients with MTS show good surgical outcomes.