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Suraj Suresh, Jennifer Sweet, Philip S. Fastenau, Hans Lüders, Patrick Landazuri and Jonathan Miller


Temporal lobe epilepsy (TLE) in the absence of MRI abnormalities and memory deficits is often presumed to have an extramesial or even extratemporal source. In this paper the authors report the results of a comprehensive stereoelectroencephalography (SEEG) analysis in patients with TLE with normal MRI images and memory scores.


Eighteen patients with medically refractory epilepsy who also had unremarkable MR images and normal verbal and visual memory scores on neuropsychological testing were included in the study. All patients had seizure semiology and video electroencephalography (EEG) findings suggestive of TLE. A standardized SEEG investigation was performed for each patient with electrodes implanted into the mesial and lateral temporal lobe, temporal tip, posterior temporal neocortex, orbitomesiobasal frontal lobe, posterior cingulate gyrus, and insula. This information was used to plan subsequent surgical management.


Interictal SEEG abnormalities were observed in the mesial temporal structures in 17 patients (94%) and in the temporal tip in 6 (33%). Seizure onset was exclusively from mesial structures in 13 (72%), exclusively from lateral temporal cortex and/or temporal tip structures in 2 (11%), and independently from mesial and neocortical foci in 3 (17%). No seizure activity was observed arising from any extratemporal location. All patients underwent surgical intervention targeting the temporal lobe and tailored to the SEEG findings, and all experienced significant improvement in seizure frequency with a postoperative follow-up observation period of at least 1 year.


This study demonstrates 3 important findings: 1) normal memory does not preclude mesial temporal seizure onset; 2) onset of seizures exclusively from mesial temporal structures without early neocortical involvement is common, even in the absence of memory deficits; and 3) extratemporal seizure onset is rare when video EEG and semiology are consistent with focal TLE.

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Dudley S. Dinner, Hans Lüders, Ronald P. Lesser, Harold H. Morris, Gene Barnett and G. Klem

✓ The relationship of intraoperative monitoring of spinal cord somatosensory evoked potentials and postoperative deficit in 220 cases (121 with scoliosis, 41 with neoplasms, and 58 others) is reported. Bilateral posterior tibial nerve stimulation was used in 181 cases and unilateral median nerve stimulation in 39. Spinal cord (interspinous ligament needles), subcortical (neck surface), and cortical (scalp surface) SEP's were monitored. Seven patients had worsening of neurological function after surgery, three of whom demonstrated significant changes in SEP's monitored. In an additional four cases, there was more than a 50% decrease in amplitude of subcortical/cortical SEP's during monitoring, but no change in neurological status postoperatively. Combined monitoring of spinal cord, subcortical, and cortical SEP's enhanced the certainty of detecting spinal cord dysfunction even though there was a significant number of false-negative and false-positive results. A marked change in the SEP's indicated a high chance of developing a neurological deficit (three or 43% of seven cases), and if there was no change the chance of any neurological postoperative deficit was extremely low (four or 1.87% of 213 cases). These data justify the use of intraoperative SEP monitoring.

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Shuichi C. Umeoka, Hans O. Lüders, John P. Turnbull, Mohamad Z. Koubeissi and Robert J. Maciunas


The goal in this study was to assess the role of longitudinal hippocampal circuits in the generation of interictal and ictal activity in temporal lobe epilepsy (TLE) and to evaluate the effects of multiple hippocampal transections (MHT).


In 6 patients with TLE, the authors evaluated the synchrony of hippocampal interictal and ictal epileptiform discharges by using a cross-correlation analysis, and the effect of MHT on hippocampal interictal spikes was studied. Five of the 6 patients were studied with depth electrodes, and epilepsy surgery was performed in 4 patients (anterior temporal lobectomy in 1 and MHT in 3).


Four hundred eighty-two (95.1%) of 507 hippocampal spikes showed an anterior-to-posterior propagation within the hippocampus, with a fixed peak-to-peak interval. During seizures, a significant increase of synchronization between different hippocampal regions and between the hippocampus and the ipsilateral anterior parahippocampal gyrus was observed in all seizures. An ictal increase in synchronization between the hippocampus and ipsilateral amygdala was seen in only 24.1% of the seizures. No changes in synchronization were noticed during seizures between the hippocampi and the amygdalae on either side. The structure leading the epileptic seizures varied over time during a given seizure and also from one seizure to another.

Spike analysis during MHT demonstrated that there were two spike populations that reacted differently to this procedure—namely, 1) spikes that showed maximum amplitude at the head of the hippocampus (type H); and 2) spikes that showed the highest amplitude at the hippocampal body (type B). A striking decrease in amplitude and frequency of type B spikes was noticed in all 3 patients after transections at the head or anterior portion of the hippocampal body. Type H spikes were seen in 2 cases and did not change in amplitude and frequency throughout MHT. Type B spikes showed constantly high cross-correlation values in different derivations and a relatively fixed peak-to-peak interval before MHT. This fixed interpeak delay disappeared after the first transection, although high cross-correlation values persisted unchanged. All patients who underwent MHT remained seizure free for more than 2 years.


These data suggest that synchronized discharges involving the complete anterior-posterior axis of the hippocampal/parahippocampal (H/P) formation underlie the spread of epileptiform discharges outside the H/P structures and, therefore, for the generation of epileptic seizures originating in the H/P structures. This conclusion is supported by the following observations. 1) Hippocampal spikes are consistently synchronized in the whole hippocampal structures, with a fixed delay between the different hippocampal areas. 2) One or two transections between the head and body of the hippocampal formation are sufficient to abolish hippocampal spikes that are synchronized along the anterior-posterior axis of the hippocampus. 3) Treatment with MHT leads to seizure freedom in patients with H/P epilepsy.