Recent Development in Neuronal Migration Disorders: Clinical, Neuroradiologic and Genetics Aspects

Disorders of neuronal migration are a heterogeneous group of disorders of nervous system development. One of the most frequent disorders is lissencephaly characterized by a paucity of normal gyri and sulci resulting in a “smooth brain”. There are two pathologic subtypes: classical and cobblestone. Classical lissencephaly results from an arrest of neuronal migration, whereas cobblestone lissencephaly results from overmigration. Another important neuronal migration disorder is heterotopia characterized by a cluster of normal neurons in abnormal locations and it is divided into three main groups: periventricular nodular heterotopia, subcortical heterotopia and marginal glioneural heterotopia. Polymicrogyria develops at the last stages of neuronal migration to the earliest phases of cortical organization; bilateral frontoparietal form is characterized by bilateral, symmetric polymicrogyria in the frontoparietal regions. Bilateral perisylvian polymicrogyria results in a clinical syndrome manifested by mild mental retardation, epilepsy and pseudobulbar palsy. Schizencephaly is another important disorder of neuronal migration whose clinical characteristics are extremely variable. Focal cortical dysplasia represents one of most severe causes of epilepsy in children. This review reports the main clinical, genetical, neuroradiological aspects of these disorders.