CENTRAL NEURONAL TUMORS IN CHILDHOOD - RELATIONSHIP TO DYSPLASIA

A survey of 1,500 brain tumors at The Hospital for Sick Children in Toronto reveals that about 20-25% of tumors demonstrate some form of neuronal differentiation. At one end of the spectrum are the well-defined ganglionic tumors, sometimes difficult to differentiate from cortical dysplasia. At the other extreme are primitive neuroectodermal tumors with neuronal differentiation often confined to immunohistochemical observations. Of the total number of tumors, approximately 5 % have a definitive ganglionic component, the majority being ganglioglioma, and others include dysembryoplastic neuroepithelial tumor, infantile ganglioglioma, paraganglioma, central neurocytoma, and gangliocytoma. Some tumors such as subependymal giant cell tumor associated with tuberous sclerosis occasionally have evidence of neuronal differentiation with immunoreactivity with antisera to neuron-specific enolase and negativity with antisera to GFAP. In children with epilepsy, improved brain imaging has identified lesions which on examination following temporal lobectomy show varying degrees of cortical dysplasia. At this site, there is also a high incidence of gangliogliomas. Is there a relationship between cortical dysplasia and neuronal tumors? Following a primary induction event during development, embryonal dysplasia and/or neoplasia may occur. The lesion may be malformative as in unilateral megalencephaly, hamartomatous as in tuberous sclerosis, neoplastic as in congenital tumors, or a combination of malformative and neoplastic. This spectrum of tumors is phenotypically recognized because of identification of the characteristics of neuronal lineage; however, the definitive relationships among these tumor groups will evolve with improved markers of differentiation and application of molecular probes highlighting the underlying lesional genotype.