Acute effect of section of the corpus callosum upon "independent" epileptiform activity

Utility of neuronavigation and neuromonitoring in epilepsy surgery

The management of medically refractory epilepsy poses both a valuable therapeutic opportunity and a formidable technical challenge to epilepsy surgeons. Recent decades have produced significant advancements in the capabilities and availability of adjunctive tools in epilepsy surgery. In particular, image-based neuronavigation and electrophysiological neuromonitoring represent versatile and informative modalities that can assist a surgeon in performing safe and effective resections. In the present article the authors discuss these 2 subjects with reference to how they can be applied and what evidence supports their use. As technologies evolve with demonstrated and potential utility, it is important for all clinicians who deal with epilepsy to understand where neuronavigation and neuromonitoring stand in the present and what avenues for improvement exist for the future.

Prognostic value of electrocorticography findings during callosotomy in children with Lennox–Gastaut syndrome

OBJECTIVE

To analyze findings and acute changes in electrocorticograms (ECoGs) obtained during corpus callosotomy in order to identify any relationships with the postoperative outcome of seizure activity.

METHODS

We retrospectively analyzed ECoGs obtained during anterior callosotomy (4-6 cm) in 48 patients with Lennox-Gastaut syndrome (32 boys and 16 girls, age 1-20 years, mean age 7.6 years) who underwent surgery between July 1993 and November 1996 to correlate recording findings with postoperative seizure activity. At the time of analysis, all patients had been followed postoperatively for more than 4 years.

RESULTS

Of 48 patients, 31 (64.6%) had significant improvement in seizure control after surgery. In pre-excisional ECoGs, 38 (79.2%) of 48 patients had bisynchronous epileptiform discharges. Patients (23 of 33 patients, 69.7%) with significant blockage of bisynchronous discharges recorded during callosotomy achieved the best postoperative seizure outcomes, but the difference did not reach statistical significance (P>0.05).

CONCLUSIONS

Based on our experience, changes in ECoG during callosotomy do not predict postoperative seizure outcome. Insignificant blockage of bisynchronous epileptiform discharges in ECoGs during callosotomy does not predict a worse prognosis than that associated with significant intraoperative blockage.

Value of intraoperative EEG changes during corpus callosotomy in predicting surgical results

The intraoperative transformation of generalized epileptiform discharges (GED) to lateralized epileptiform activity during the course of corpus callosum sectioning for intractable epilepsy in 37 patients was correlated with percentage of decrease in atonic-tonic seizures with "drops" at mean follow-up of 26 months (range 12-86 months). Twenty-seven (73%) patients had intraoperative interictal discharges, and 21 (78%) showed varying degrees of lateralization of GED during corpus callosum sectioning (two thirds to total). All patients experienced > 80% reduction in atonic-tonic seizures with drops. The group (n = 7) with largest decrease in GED had the greatest decrease in seizures (95.5%). Six patients without change in GED had 88% decrease in seizures, as did 14 patients (85-86%) with mild or moderate decreases in GED, but there was no statistically significant correlation between decrease in GED and seizure frequency after operation. Thus, although lateralization of GED after corpus callosum sectioning was evident in 78% of patients with GED, the degree of lateralization of GED did not correlate with degree of reduction of tonic-atonic seizures. Therefore, intraoperative surface EEG monitoring does not appear to be helpful at this time as a guide to extent of callosotomy.

The relevance of secondary epileptogenesis to the treatment of epilepsy: kindling and the mirror focus

Human beings with partial epilepsy and demonstrable cerebral lesions show, in addition to ipsilateral epileptiform EEG discharges, apparently independent epileptiform discharges from the opposite hemisphere. Patients with apparent unilateral focal onset of their partial seizures but without demonstrable lesions also frequently display what appear to be bilaterally independent EEG foci. When surgical treatment or medical prognosis is considered and there is no demonstrable lesion, the decision of which of the two apparent foci is primarily responsible for the seizures is often difficult. Even with a known structural lesion the question arises whether, following its removal, the contralateral focus will persist and will be epileptogenic. Two related experimental phenomena bear directly on these questions- kindling and the mirror focus. This presentation looks critically at existing evidence and finds that it fails to support the idea that kindling and the mirror focus have roles in human epilepsy that currently should influence clinical decisions.

Forebrain commissurotomy for epilepsy. Review of 20 consecutive cases

During the past 10 years, 20 patients with intractable generalized, generalized and partial, and partial seizures have been treated here by surgical division of one or more of the forebrain commissures. Modifications in the operative technique and extent of operation have resulted in continued good results in seizure control with decreased morbidity. The present operation, a two-stage division of the corpus callosum and underlying hippocampal commissure, is demonstrated to be effective in controlling intractable seizures. Good or excellent results account for more than 80 per cent of the series. Historical background, indications for operation, criteria for patient selection, operative technique, results, complications, and the value of forebrain commissurotomy as a research tool are presented.