Clinical Study
Post-section recruitment of epileptiform discharges in electrocorticography during callosotomy in 48 patients with Lennox–Gastaut syndrome

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Abstract

We aimed to clarify the relationships between post-sectional recruitment of epileptiform discharges (PRED) seen in electrocorticograms (ECoG) during callosotomy in patients with Lennox–Gastaut syndrome (LGS) and postoperative seizure outcome. We retrospectively analyzed ECoG obtained during subtotal callosotomy (6 cm) in 48 patients with LGS (32 males, 16 females; age range, 1–20 years; mean age, 7.6 years) from July 1993 to November 1996 and compared recorded findings with postoperative seizure outcome. At analysis, all patients had been followed postoperatively for more than 10 years. Of 48 patients, 15 (31.3%) had PRED in their post-section ECoG. Of these patients, 11 (73%) achieved significant (at least 50%) overall seizure reduction postoperatively. The phenomenon of PRED in callosotomy did not predict a better postoperative seizure outcome (p > 0.05). We concluded that post-sectional ECoG recruitment of electrical discharges during callosotomy did not predict postoperative prognosis. However, this finding should be supported and elucidated by further studies. The heterogenous ECoG findings during callosotomy in our series might suggest a complicated role of the corpus callosum in the epileptogenesis of Lennox–Gastaut syndrome.

Introduction

Although acute electrocorticography (ECoG) is often used during epilepsy surgery, there is no consensus as to its value and criteria for its interpretation. Fiol et al. used intraoperative surface electroencephalogram (EEG) monitoring as a guide to the extent of callosotomy and concluded that it was not helpful.1 Binnie et al.2 used ECoG recordings to determine the effects of callosotomy on the bilateral synchrony of epileptiform discharges (ED) detected before the procedure. Although a better clinical outcome was observed among patients in whom the bilateral synchrony of ED was disrupted by callosal section, they questioned the validity of this result because of possible biased findings in their small series. Kwan et al.3 found that greater blockage of bisynchronous ED per ECoG did not predict better postoperative prognosis in their 48 patient series. In a preliminary study, Binnie et al.2 found that ECoG spike rates following multiple subpial transections varied from complete abolition to a 200% increase, without a demonstrable relationship to either seizure outcome or completeness of transection. MacDonald and Pillay4 reported their experience with intraoperative ECoG in the setting of temporal lobe epilepsy surgery and suggested that post-excision activation (the new appearance of ED with a different location, morphology, and behavior than before resection) in the ECoG of these patients appears to be a good prognostic sign, although their findings were not statistically significant. Shyu et al.5 reported that electrocorticographic seizures immediately following callosotomy may not predict a poor surgical outcome. To our knowledge no previous report has documented the phenomenon of post-section activation and/or similar findings in callosotomy. We conducted this study to retrospectively analyze ECoG obtained during anterior callosotomy in 48 patients with Lennox–Gastaut syndrome (LGS) from July 1993 to November 1996. The phenomenon of post-section recruitment of epileptiform discharges (PRED) – ECoG spike rates increasing to 200% or more, but not new ED with a different location, morphology, and behavior than before section – has been identified and the relationship between PRED in ECoG and postoperative seizure outcome has also been evaluated.

Section snippets

Selection of patients

The present series was drawn from all eligible patients who underwent an anterior corpus callosotomy at the Taipei Veterans General Hospital, Taipei, Taiwan, between July 1993 and November 1996. All patients had medically intractable seizures with epileptic falls as part of their presentation of LGS, a syndrome that is defined by an electroclinical triad of generalized slow spike-and-wave complexes in the EEG, multiple types of epileptic seizures, and slow mental development. Medical

Results

The 48 patients (33 males and 15 females) ranged in age from 1 year to 20 years (mean, 7.6 years). The onset of epilepsy ranged from <1 day of age to 10 years (mean, 2.0 years). Duration between onset of epilepsy and callosotomy ranged from 1 year to 14 years (mean, 5.6 years). Total postoperative follow-up time ranged from 4 years to 7.5 years (mean, 5.8 years).

When postoperative seizure outcome was graded, no patient qualified for Grade 1 or Grade 6: nine patients (19%) were Grade 2; 22 (46%) were Grade

Discussion

In the epileptic brain, the CC is assumed to have a role in bilateral synchronization of seizure activities. The CC has been thought to be the major pathway for the spread of ED from one hemisphere to the other during bilateral generalization.6 Several later reports regarding callosotomy have supported this view: callosotomy can significantly reduce bilaterally synchronous generalized ED.[7], [8], [9] This transfer role of CC is compatible with the findings of some of our patients in Groups 1

Acknowledgements

We are grateful to Miss Wen-Yung Sheng for her statistical analysis.

References (19)

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  • Predictive role of brain connectivity for resective surgery in Lennox–Gastaut syndrome

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    Group A exhibited unilateral sources by dDTF in most cases, whereas group B exhibits bilateral sources, although pre-callosotomy EEG visually revealed bilateral synchronized GSWs in both groups. The corpus callosum seems to play an important role in bilateral synchronization via interhemispheric recruitment of a preexisting PEA in hemispheric epileptogenicity, as shown in both groups (Ono et al., 2002; Lin and Kwan, 2012). Therefore, dDTF allowed us to predict the changes in the epileptic network after callosotomy in LGS.

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    Little has been reported on the real-time EEG change during sequential steps of corpus callosotomy. Lateralization or blockade of bisynchronous epileptiform discharges were observed intra-operatively after callosal section (Fiol et al., 1993; Lin and Kwan, 2012). EEG changes were analyzed by visual inspection, and correlation of post-operative seizure outcome attempted.

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