A New Approach in Clinical Usefulness of Foramen Ovale Electrode in Epilepsy Surgery

Kim, Ok Jun; Lee, Byung In

Abstract

BACKGROUND: Foramen ovale electrode(FOE) was introduced for the lateralizing purposes of mesio-temporal lobe(MTL) seizures which were often not clearly identified by extracranial EEGs. An analysis of interictal and ictal EEG features recorded from FOE was conducted to evaluate its clinical usefulness.
METHODS
A multipolar, three-contact FOE was implanted bilaterally in 16 intractable epileptic patients for the lateralizing purposes of a MTL onset of seizures due to the evidence of bilateralities recorded from extracranial EEGs. A detailed analysis of the electrical pattern and temporal relationships in 16 patients was conducted.
RESULTS
After a long-term telemetry recording with FOE, all patients revealed a clear onset of seizures originating from one or both sides of the MTL and underwent ATL. The lateralization of interictal epileptiform discharges (IEDs) in scalp EEG and FOE were concordant with the operation sites in 12 patients and 8 patients respectively. Among various configurations of IEDs recorded from FOE, periodic spikes or sharp waves with/without fast activities were dominant features in the operation site, but polyspikes, isolated spikes or sharp waves, and positive spikes were more common in the non-operation site. Five patients showed ictal onset discharges concordant with the operation site in the scalp EEG, but 10 patients in FOE. Rhythmic fast beta, alpha frequency activity, repetitive spikes or sharp waves prevailed over other FOE seizure onset patterns in the operation site, but delta and theta slowing, positive spikes prevailed in the non-operation site. A "start-stop-start" pattern was 100% concordant with the operation site. The time interval between bilateral FOE recorded ictal onset was 16.53 sec when the ictal discharge started from the operation site and 7.92 sec when started from the non-operation site. The time interval between FOE and scalp EEG ictal onset was 22.82 sec in the operation site and 8.61 sec in the non-operation site. Among various spreading patterns of ictal epileptiform discharge, FOE contralateral FOE ipsilateral temporal lobe, or contralateral temporal lobe was the most common feature(47.71%). No serious complications resulted from implantation of FOE in this series.
CONCLUSIONS
Our results indicated that FOE was very useful in confirming the laterality of MTL. The configurations of IEDs and ictal discharges recorded from FOE were also useful for further determination of lateralization. The "start-stop-start" pattern of ictal discharges was especially a quite reliable marker, which should be cautiously detected during the analysis of ictal events. FOE could also provide useful information about the spreading patterns of ictal discharges.