Brain, Vol 120, Issue 12 2259-2282, Copyright © 1997 by Oxford University Press
G Alarcon, JJ Garcia Seoane, CD Binnie, MC Martin Miguel, J Juler, CE Polkey, RD Elwes and JM Ortiz Blasco
Although acute electrocorticography (ECoG) is routinely performed during
epilepsy surgery there is little evidence that the extent of the
discharging regions is a useful guide to tailoring the resection or that
the findings are predictive of outcome or pathology. Patterns of discharge
propagation have, however, rarely been considered in assessing the ECoG. We
hypothesize that regions where discharges show earliest peaks ('leading
regions') are located in the epileptogenic zone, whereas sites in which
late, secondary, propagated activity occurs have less epileptogenic
potential and do not need to be excised. To allow intraoperative
topographic ECoG analysis, a computer program has been developed to
identify leading regions and the sites showing greatest rates or amplitudes
of spikes. Their topography has been compared retrospectively with
pathology and seizure control in 42 consecutive patients following temporal
lobe surgery. Leading regions were most often found in the hippocampus, the
subtemporal cortex and the superior temporal gyrus. The most common
propagation patterns were from hippocampus to subtemporal cortex and vice
versa. There was no association between seizure outcome and the location of
regions with greatest incidence or amplitude of spikes or location of
leading regions. There was, however, a strong and significant association
between poor outcome and non-removal of leading regions other than those in
the posterior subtemporal cortex. All leading regions (other than posterior
subtemporal) were resected in 27 patients of whom 25 had a favourable
outcome. Leading regions (other than posterior subtemporal) remained in 14
patients of whom only four had a good outcome. One patient had no
epileptiform activity in the ECoG and good outcome. Persistent posterior
subtemporal leading regions remained in nine subjects; all had favourable
outcome (Grades I or II) but only three were seizure free. These results
suggest that: (i) interictal epileptiform discharges may originate from a
complex interaction between separate regions, resulting in propagation and
recruitment of neuronal activity along specific neural pathways; (ii)
removal of all discharging areas appears unnecessary to achieve seizure
control provided that leading regions (other than posterior subtemporal)
are removed; and (iii) identification of such leading regions could be used
to tailor resections in order to improve seizure control and reduce
neurological, neuropsychological and psychiatric post-surgical morbidity.
ARTICLES
Origin and propagation of interictal discharges in the acute electrocorticogram. Implications for pathophysiology and surgical treatment of temporal lobe epilepsy
Institute of Epileptology, King's College, London, UK.
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