Abstracts

RATIONALE: To report two cases of patients with medial temporal lobe epilepsy in whom subdural electrode recordings (SDE) were falsely lateralizing. METHODS: We present two encountered cases of medically refractory partial seizure patients who had invasive recordings as part of their pre-surgical work-up. We reviewed their scalp and invasive recordings as well as their other ancillary testing (MR and PET scans). RESULTS: In the first case ictal scalp recordings suggested left temporal seizures but was 1 minute after the clinical onset. This finding necessitated the use of SDE. Recordings using SDE only demonstrated right temporal seizure onset that was disconcordant with the MR and PET findings. Subsequent depth recording revealed left medial temporal onsets. Left temporal lobectomy has resulted in seizure freedom for more than 4 years. Simultaneous depth and SDE recordings in the second case showed left medial temporal onsets by the depth electrodes. This was followed by a right lateral temporal seizure activity only seen by the SDE in 3-20 seconds. MR and PET scans in this case were normal. Left temporal lobectomy resulted in a 50% reduction of the baseline seizures. CONCLUSIONS: Subdural electrodes can be falsely lateralizing in cases of medial temporal epilepsy. Depth recording in agreement with other studies is the most accurate method to lateralize and identify the seizure focus in this group of intractable epilepsy patients; however, SDE should be combined with depth electrodes in TLE when the diagnosis of MTS is not suggested clinically or by the use of other ancillary testing.