Abstracts

RATIONALE: Focal cortical dysplasias (CD) are frequent pathological substrates of medically intractable epilepsy. The in situ epileptogenicity of these lesions as well as its relationship with histopathological changes remains unknown. The purpose of this study is to correlate the cellular patterns of CDs with the expression of focal cortical epileptogenicity as assessed by direct extraoperative electrocorticographic (ECoG) recordings using subdural grids. METHODS: The histopathological, morphological, and immunocytochemical findings in cortical tissue resected from 18 patients with medically intractable epilepsy due to CD were correlated with in situ ECoG patterns recorded from subdural grids. Epileptogenic areas exhibiting ictal (with or without interictal spikes) activities were identified and separated during surgery from non epileptic cortical regions. RESULTS: Epileptogenic cortical areas were characterized by abnormalities of horizontal and columnar dyslamination, dysmorphic neurons, higher NMDA 2A/B subunit immunoreactivity in all cases studied. Six patients had evidence of balloon cells in the cortical mantle and the subcortical white matter. Balloon cells were found in the epileptogenic specimens in only 2/6 patients. The balloon cells showed immunocytochemical features characteristic of both glial and neuronal cells. CONCLUSIONS: This study provides evidence for the cellular changes in epileptic CDs and show the heterogeneity in the expression of epileptogenicity in various histopathological substrates of CDs. Epileptogenicity was mainly restricted to the dysplastic areas devoid of balloon cells in the majority of patients. The presence of severe cellular abnormalities (balloon cells) is not usually associated with in situ epileptogenicity. Further studies are needed to elucidate the nature and the potential role(s) of balloon cells in CD-induced epileptogenicity.