Neuronal Migration Disorders.

Enhanced understanding of brain development has led to increased awareness of the links between disorders of neuronal migration and seizure disorders. A significant number of patients with intractable epilepsy have cortical malformations that originated during neuronal migration. Magnetic resonance imaging plays a primary role in the diagnosis and classification of neuronal migration disorders. These disorders include polymicrogyria, schizencephaly, lissencephaly, heterotopia, and focal cortical dysplasia. Imaging protocols continue to evolve to provide critical assessment of anatomic and physiologic traits of these disorders to better treat and prevent seizures.

[Developmental malformations of the cerebral cortex]. / Heterotopie, Polymikrogyrie, Lissenzephalie und Co - Malformationen der kortikalen Hirnentwicklung.

Migration disorders (MD) are increasingly recognized as an important cause of epilepsy and developmental delay. Up to 25 % of children with refractory epilepsy have a cortical malformation. MD encompass a wide spectrum with underlying genetic etiologies and clinical manifestations. Research regarding the delineation of the genetic and molecular basis of these disorders has provided greater insight into the pathogenesis of not only the malformation but also the process involved in normal cortical development. Diagnosis of MD is important since patients who fail three antiepileptic medications are less likely to have their seizures controlled with additional trials of medications and therefore epilepsy surgery should be considered. Recent improvements in neuroimaging have resulted in a significant increase in the recognition of MD. Findings can be subdivided in disorders due to abnormal neurogenesis, neuronal migration, neuronal migration arrest and neuronal organization resulting in different malformations like microcephaly, lissencephaly, schizencephaly and heterotopia. The examination protocol should include T 1-w and T 2-w sequences in adequate slice orientation. T 1-w turbo-inversion recovery sequences (TIR) can be helpful to diagnose heterotopia. Contrast agent is needed only to exclude other differential diagnoses.