Unusual MRI appearance of diffuse subcortical heterotopia or "double cortex" in two children.

Two children with mild epilepsy and learning and behaviour problems had magnetic resonance imaging (MRI) scans showing an almost identical generalised disorders of neuronal migration. Their computer tomography (CT) scans showed abnormal hypodense white matter. The MRI showed a four layered appearance of the cerebral parenchyma extending from the frontal to the occipital region. There was a normal appearance to the white matter in the periventricular region which had an abnormally smooth junction with a thick diffuse layer of heterotopic grey matter. This was surrounded by a thin layer of white matter which had normal digitations with the overlying cortex. The appearance of the overlying cortex was normal. These and other recently described cases broaden the concept of generalised disorders of neuronal migration and illustrate that it is possible to have a generalised cerebral malformation with few clinical consequences.