Abstracts

Rationale: Patients with suspected temporal lobe epilepsy are good candidates for surgical evaluation when medications fail to control seizures, provided seizures are unilateral and concordant with any MRI structural lesion. Phase II video-EEG with foramen ovale electrodes often helps to resolve the uncertainties about mesial temporal onsets. We are struck by the proportion of cases with discordant or bilateral onsets revealed by FOE even in the face of a unilateral temporal MRI lesion such as MTS. These cases may explain the gap in seizure free outcome when ideal candidates undergo temporal lobectomy.Methods: We evaluated 63 patients age 18-69 for video-EEG monitoring with 10-20 scalp and multicontact foramen ovale electrodes. All patients had previously undergone phase I evaluation for possible epilepsy surgery. Noninvasive phase I video-EEG frequently gave evidence of poorly lateralized or localized seizure onsets or a delayed ictal pattern compared to clinical onset. All were interested in temporal lobectomy if candidates. We analyzed patients according to seizure onset, duration of epilepsy, seizure frequency, MRI findings, phase I findings, and phase II findings; surgical patients were classified according to outcome.Results: MRI findings: 36 of 63 patients had MTS (13 Right/23 Left). 8 were nonlesional and 19 were lesional other than MTS. No patients had bilateral temporal MRI lesions. Seizure onsets: 18 patients had bilateral independent temporal onsets detected by FOE. 8 of these had unilateral MTS. 5 had no focal lesions. 5 had unilateral temporal lesions other than MTS. 1 patient had unilateral temporal lesions with discordant EEG onset from the opposite side. Of these, 18 were suspected on phase I to be discordant, either by EEG or clinical features. Surgical outcomes: 24 patients with FOE verified unilateral seizure onsets underwent temporal lobectomy. 92 % are seizure free (Engels class 1a-c) with a minimum or 6 months follow up. None of the variables listed above were reliably predictive of bilateral seizure onsets in this sample.Conclusions: Advances in MRI technology have led to easier detection of brain lesions that may correspond to epileptogenic foci. There is a temptation to accept noninvasive ictal recordings and MTS or other focal structural abnormalities as sufficient to identify surgery candidates. Our data with FOE recordings emphasizes that up to 27 % of patients with MTS or other focal temporal lesions have bilateral independent seizure onsets revealed by FOE. The proportion and clinical consequences of the seizures from the unexpected contralateral seizure focus must be considered on an individual basis when considering surgery for patients with bilateral seizure onsets.