Hippocampal sclerosis in children with lesional epilepsy is influenced by age at seizure onset

Purpose: Hippocampal sclerosis (HS) is the most common lesion underlying drug-resistant temporal lobe epilepsy. Whether HS is a developmental or acquired pathology remains unclear. Whereas HS has been causally linked to prolonged febrile convulsions in childhood, evidence also exists that it may coexist with extrahippocampal abnormalities, the concept of dual pathology. The aims of this study were to address whether hippocampal abnormality consistent with HS (a) occurs in children with lesional extrahippocampal epilepsy, (b) is more commonly seen in association with developmental rather than acquired extrahippocampal pathologies, and (c) whether any effect of age at seizure onset is found on the occurrence of HS in lesional extrahippocampal epilepsy. Methods: Clinical and histopathologic data of patients having resective surgery for extrahippocampal epilepsy that included the hippocampus were investigated. Results: Twenty-nine children were retrospectively included in this study, and 21 (72%) of 29 were found to have a hippocampal abnormality consistent with HS. No relation was noted between developmental or acquired extrahippocampal pathologies and the presence of hippocampal abnormality. Children with normal hippocampi on visual histologic assessment had a significantly younger age at seizure onset (p < 0.001). Duration of epilepsy was not correlated with the presence of hippocampal abnormality. Conclusions: Hippocampal abnormalities are seen in similar proportions with both acquired and developmental extra-hippocampal pathologies, suggesting that these abnormalities are the result of seizures from the focus that is remote from the hippocampus. In addition, children who have their initial seizure at an early age are less likely to develop seizure-induced hippocampal injury.