Glioneuronal malformative lesions and dysembryoplastic neuroepithelial tumors in patients with chronic pharmacoresistant epilepsies.

Malformative glioneuronal lesions were examined in surgical specimens from 43 patients with chronic focal epilepsies in order to determine the scope of histopathological changes and to better understand their pathogenesis. The most common lesions were hamartias composed of randomly oriented neurons and astrocytes (24 cases). Most of these lesions also contained clustered oligodendrocyte-like cells which were often strongly immunoreactive for the developmentally regulated embryonal form of the neural cell adhesion molecule (E-NCAM). These hamartias were typically minute, multifocal, and arranged in a pattern suggestive of a migration disorder. There were eight cases with aggregates of large disfigured neurons, oversized atypical astrocytes and ballooned multinucleated giant cells reminiscent of tuberous sclerosis-associated changes. Finally, there were 11 dysembryoplastic neuroepithelial tumors (DNT), an entity which has been proposed to be malformative rather than neoplastic. The oligodendroglia-like cells in DNT were negative for E-NCAM. However, strong E-NCAM expression was present in many dysplastic neurons of tuberous sclerosis-like lesions, hamartias and DNT and in reactive astrocytes. Significant immunoreactivity for the proliferation associated Ki-67 antigen was not observed. No similar lesions were observed in 500 consecutive autopsies from patients without epilepsy. Malformative glioneuronal lesions appear to be highly epileptogenic and most likely result from a disordered cell migration and differentiation.