Pathologic features of dysplasia and accompanying alterations observed in surgical specimens from patients with...

Malformations caused by abnormalities of cortical development, or cortical dysplasias, were examined in surgical specimens from 108 patients with medically intractable epilepsy to determine the scope of histopathologic changes. The relevance of the clinical findings was also evaluated. Various types and degrees of dysplastic features were observed in various combinations, including architectural abnormalities, an increased number of neurons in the molecular layer and/or cortical layer II, neuronal clustering, an increased number of satellite oligodendrocytes, abnormal gyration, single and/or aggregates of heterotopic neurons in the white matter, and the appearance of cytologically abnormal cells, such as giant or dysmorphic neurons and balloon cells. In the temporal lobe specimens, microdysgenesis (corresponding to mild malformations caused by abnormalities of cortical development and type IA/B focal cortical dysplasias) was more frequently observed than Taylor-type focal cortical dysplasia (type IIA/B), whereas in the frontal lobe specimens, the frequency of occurrence of both types was even. The ages at seizure onset and surgery of patients with the latter type were significantly lower than those of patients with the former. On the other hand, prominent astrocytosis in the cortex and white matter was evident in all cases, and many corpora amylacea and neurofibrillary tangle-like inclusions were observed in a subset of cases. An ultrastructural investigation revealed dilatation of the postsynaptic dendritic spines and shafts in the cortex and features indicating the occurrence in the white matter of demyelination followed by remyelination. Thus, with regard to the epileptogenic lesions, although dysplastic changes constitute the pathogenetic basis, the overlapping subsequent degenerative processes involving synapses, dendrites, and axons might contribute to the development of epileptogenic processes. Astrocytes might also actively participate in the development of the pathogenesis of epilepsy.