Abstracts

RATIONALE: We correlated the spatial distribution of epileptic discharges recorded by magnetic source imaging / magnetoencephalography (MSI/MEG) with the pathology of epileptogenic lesions for the possible differentiation of lesions by location of MEG spikes.
METHODS: We reviewed the records of all patients for intractable localization-related epilepsy who underwent examination by MSI between April 1993 and October 2001 and subsequent surgery. Twenty-four of these subjects satisfied additional selection criteria for this study: (1) neuropathology results of epileptogenic lesions, (2) pre-operative MSI, and (3) pre-operative MRI with abnormalities. Two neuroradiologists and one epileptologist retrospectively reviewed pre-operative MRI and MSI for each of these patients simultaneously. The spatial distribution of epileptic spike sources was evaluated by consensus. Epileptic spike sources were classified into clusters of [gt]5 spikes, or those without a clustered configuration. Spikes were further categorized into three groups, according to their spatial relationship to epileptogenic lesions: (a) those within and extending from the lesion, (b) those along the marginal zone, defined as =[lt]2 cm from the lesion, and (c) those in an ipsilateral extramarginal area, defined as [gt]2cm from the lesion.
RESULTS: Demographic data for the 24 subjects was as follows: mean age at time of MSI study 10.8 +/- 4.2 years (mean +/- SD, range 4.6 - 17.4), and F : M ratio = 9:15. Pre-operatively, all patients suffered from partial epilepsy, with complex partial type in 11 (45.8%). Secondarily generalized epilepsy occurred in 12 (50.0%). Neuropathology of epileptogenic lesions consisted of: cortical dysplasia (CD) in 14 (58.3%), tumor (low grade astrocytoma or dysembryoplastic neuroepithelial tumor (DNET)) in 7 (29.2%), and infarct or porencephalic cyst in 4 (16.7%). One of the patients had a combination of DNET and CD. Spikes located within lesions, whether clustered or not clustered, were noted in 13 (92.9%) of the subjects with CD. Clustered epileptic spike sources originating within lesions were only present in patients with CD. Two patients (28.6%) in the tumor category displayed spikes within their lesions (Fisher[ssquote]s test, p[lt]0.01), and histology revealed DNET in both, with one having the mixed pathology (DNET and CD) noted above. None of the patients with infarcts displayed spikes within their lesions. Ipsilateral marginal spikes were present in 6 (85.7%) of the patients with tumors, 2 (50.0%) with infarcts, and 6 (42.9%) with CD. Ipsilateral extramarginal spikes were present in 6 (85.7%) of the patients with tumors, 1 (25.0%) with infarct, and 6 (42.9%) with cortical dysplasias.
CONCLUSIONS: The spatial distribution of epileptic spikes sources on MSI/MEG of children with localization-related epilepsy is helpful in distinguishing cortical dysplasia from other epileptogenic lesions. Spikes, especially clustered ones, originating from within epileptogenic lesions are significantly more associated with cortical dysplasia, whereas marginal spike sources are more indicative tumor. This information can also assist in the trajectory and the extent of resection during epilepsy surgery.