Abstracts

Rationale: Corpus callosotomy is aimed to disrupt inter-hemispheric propagation of epileptic activities generating tonic, atonic or gecondarily generalized seizures. Section of corpus callosum often results in dramatic changes in interictal spikes, for example desynchronization or lateralization of bilateral spikes. Recent case reports suggested that such post-callosotomy changes of epileptiform discharges may uncover epileptic foci in one hemisphere which secondary leads to respective epilepsy surgery. The purpose of this study is to reveal the relationship between the interhemispheric latency of bisynchronous spikes and post-callosotomy changes of those spikes. Methods: The study included 6 patients with intractable generalized epilepsy (3 cryptogenic and 3 symptomatic cases) who had infantile or early childhood onset of disease and received one-stage total corpus callosotomy for the alleviation of seizures. The age at surgery was ranged from 1 year 5 month to 15 years. Inter-hemispheric latency of interictal spikes were calculated in the pre-operative EEG, and compared with post-operative EEG. Results: Pre-operative EEG was characterized by generalized or bihemispheric multi-focal spikes in all cases. Post-operatively, spikes were lateralized to one hemisphere in 2 and became bilaterally independent in 2 cases. No notable changes were found in the remaining 2 cases. In the 2 cases with post-operative lateralization, pre-operative spikes were characterized by one-way propagation of spikes, i.e. spikes propagating from one hemisphere to the other hemisphere, and lateralization occurred to the hemisphere with leading spikes. Inter-hemispheric latency was generally within 20 ms in all cases. There was no clear association of the latency and the pattern of propagation to post-operative outcome. Conclusions: Generalized spikes with one-way propagation pattern results in lateralization of the spikes to the leading hemisphere after corpus callosotomy. This type of post-operative EEG changes may reveal epileptogenic foci in one hemisphere post-operatively.