Neuropathological spectrum of focal cortical dysplasia in children with severe focal epilepsies

Abstract

Cortical dysplasias comprise a variable spectrum of clinical, neuroradiological and histopathological findings. We report about a cohort of 25 pediatric patients (mean age 8.1±4.8) with severe drug resistant early onset focal epilepsies (mean age 2.1±0.4), mental/psychomotor retardation, and multilobar epileptogenesis. Microscopical inspection of neurosurgically resected specimens revealed dysplastic neurons with/without balloon cells in only seven patients, i.e. focal cortical dysplasia (FCD) type II according to Palmini et al. 2004. All other patients presented with rather subtle neuroanatomical abnormalities. Regular findings were increased numbers of ectopic neurons in white matter and increased numbers of microcolumns in cortical lamina III. Another consistent observation identified small vessels with enlarged perivascular space but no evidence for blood brain barrier impairment as well as severe cortical gliosis. We propose to classify these findings according to FCD type I. However, to identify histological abnormalities during postnatal maturation of the brain challenges any neuropathological classification in this group of young patients. Our observations in this subgroup of pediatric patients support a concept compatible with regional loss of high order brain organization. As a consequence, post-operative seizure control is more difficult to achieve in this cohort compared to patients with better defined FCD type II.