Comparison of Intracranial Ictal EEG Patterns between Medial and Lateral Temporal Lobe Epilepsy

Song, Jin Kyu; Mihara, Tadahiro

Abstract

BACKGROUND AND OBJECTIVES: Temporal lobe epilepsy is the most common uncontrolled epileptic condition and is increasingly treated with surgery. In the absence of definitive results from noninvasive procedures, patients undergo implantation of intracranial electrodes. Intracranial EEG recordings are more accurate than scalp EEG recordings because of minimal artifact and closer approximation to the area of seizure onset. Intracranial EEG patterns between the medial and the lateral temporal lobe epilepsy were thought to have a little differences.
METHODS
The authors compared the morphological pattern of seizure onset area, spread pattern, termination pattern and duration of the intracranial EEG manifestation of spontaneous seizures recorded from combined depth and subdural electrodes in 25 intractable temporal lobe epilepsy patients.
RESULTS
Sixteen cases were medial temporal onset, six cases were neocortical onset and three cases were multifocal onset. The morphological onset pattern of medial temporal seizures was more likely to have high frequency rhythmic discharge (>13 Hz) and tended to show repetitive spikes prior to the seizure, whereas neocortical seizures were characterized by slow (4-to 10-Hz) and fast frequencies (>35 Hz), without evidence of repetitive spikes. The mean ictal duration at seizure onset of complex partial seizure of medial onset seizure was 121 seconds and was not different from those of neocortical seizures which were 115 seconds. Neocortical seizures take more time to propagate than medial seizures. Propagation to the opposite side of neocortical onset seizure takes 45.53 seconds, whereas medial temporal onset seizure takes 27.92 seconds. In case of second generalization, neocortical seizures continued longer than medial seizures. Of the medial onset temporal lobe seizures, except the simple partial seizures, the 35.2% of seizures initially spread to ipsilateral neocortex, and the 28.2% of seizures initially spread to the contralateral medial temporal lobe and the 25% of seizures simultaneously propagated to the ipsilateral neocortex and contralateral medial temporal lobe. Among the seizures initiated from the neocortex, 79.3% of seizures initially spread to the ipsilateral medial temporal area, but never initially spread to opposite neocortex. The termination pattern of seizures was divided into three types according to their location. In case of medial temporal lobe seizures, the mean of 31% of seizures was diffusely terminated , 38% of seizures terminated at the onset region and 38% of seizures were elsewhere within onset region. On the other hand, 48.6% of neocortical temporal lobe seizure were terminated at seizure onset region.
CONCLUSIONS
The pattern of ictal intracranial EEG provides distinguishable differences between the medial temporal seizure and the neocortical temporal seizure.