Focal cortical dysplasia: neuropathological subtypes, EEG, neuroimaging and surgical outcome

Abstract

Since the original description by Taylor, the term focal cortical dysplasia has been used to refer to a wide range of alterations of the cortical mantle. More recently, these conditions have been described from neuroimaging, neuropathological and genetic standpoints, generating several classifications. It is widely recognized that these classifications are unsatisfactory. We propose a simplified classification of focal cortical dysplasias based on easily recognized neuropathological characteristics. We retrospectively re-examined histological sections of cortex from 52 of 224 (23%) patients operated on for drug-resistant partial epilepsy in which cortical dysplasia was present but not associated with other brain pathologies except hippocampal sclerosis. Three subgroups were identified: (i) architectural dysplasia (31 patients) characterized by abnormal cortical lamination and ectopic neurones in white matter; (ii) cytoarchitectural dysplasia (six patients) characterized by giant neurofilament-enriched neurones in addition to altered cortical lamination; and (iii) Taylor-type cortical dysplasia (15 patients) with giant dysmorphic neurones and balloon cells (all but two patients) associated with cortical laminar disruption. The patients with architectural dysplasia had lower seizure frequency than those with cytoarchitectural and Taylor-type dysplasia, and the epileptogenic zone was mainly in the temporal lobe. In patients with Taylor-type dysplasia, the epileptogenic zone was mainly extratemporal, and interictal stereo-EEG was distinctive. MRI was unrevealing in 34% of patients, but distinctive signal alterations characterized most patients with Taylor-type dysplasia, while focal hypoplasia with MRI abnormalities was found in architectural dysplasia. Patients with Taylor-type dysplasia had the best outcome, with 75% seizure-free (Engel class Ia) after at least a year of follow-up compared with 50% of cytoarchitectural dysplasia and 43% of architectural dysplasia patients seizure-free. This three-category classification is based on easily recognized histopathological characteristics and avoids complicated terminology, while the distinctive ensemble of other characteristics defines clinically homogeneous groups.

GABAergic synchronization in the limbic system and its role in the generation of epileptiform activity

“…For instance, a synchronous GABA A receptormediated event appears to be able to initiate ictal discharges in post-surgical neocortical tissue removed from patients with Taylor type focal cortical dysplasia (Avoli et al, 1999;D'Antuono et al, 2004); it was shown in these experiments that, as reported in rodent limbic structures, this synchronous GABAergic potential is accompanied by a transient increase in [K + ] o as well as that the ictal activity is abolished by GABA A receptor antagonists or μ-opioid receptor agonism. Interestingly, it has been reported that the dysplastic tissue resected from these patients presents with decreased number of presumptive interneurons that, however, provide increased GABAergic innervation to principal cells (Spreafico et al, 1998;Tassi et al, 2002). In addition, Alonso-Nanclares et al (2005) have reported that giant ectopic neurons in the white matter are surrounded by hypertrophic basket formations.…”

Epilepsy Related to Developmental Tumors and Malformations of Cortical Development

“…Since the first description of the neuropathologic features of FCD provided by Taylor et al in 1971 [95], different FCD classification systems have been proposed [93,94,[96][97][98]. A task force of the Diagnostic Methods Commission of the International League Against Epilepsy (ILAE) has recently generated a new consensus classification of distinct FCD subtypes based on histopathological features [6].…”

Avaliação da arquitetura do sono em crianças com epilepsia refratária

“…12 Estas duas formas foram melhor caracterizadas do ponto de vista clínico, neuropsicológico e especialmente de imagem, permitindo, frequentemente, uma antecipação diagnóstica in vivo das anormalidades histológicas. 13 No outro extremo estão as epilepsias causadas por lesões não desenvolvimentais. A lista de lesões epileptogênicas não desenvolvimentais é extensa e as mais comuns são a ulegiria atrófica ou cicatriz porencefálica, resultantes de insulto hipóxico-isquêmico prévio, esclerose temporal mesial, tumores não-desenvolvimentais e lesões vasculares, incluindo Síndrome de Sturge Weber, além de lesões resultantes de infecções congênitas ou adquiridas.…”

“…59 As descargas parecem ser o resultado de interações complexas entre a heterotopia e o neocórtex e estudos utilizando EEG intracranial demonstraram que a substância cinzenta heterotópica é capaz de gerar atividade elétrica usualmente sincronizada mas também independente do córtex adjacente. 13,59,60 Embora os mecanismos exatos pelos quais as crises causem alterações na arquitetura do sono não sejam totalmente compreendidos é provável que desequilíbrios neuropatológicos, como os encontrados nas malformações corticais, como perda ou desorganização celular, sejam a base para os transtornos do sono associados à epilepsia. 61 …”