Cerebellar cortical neurons misplaced in the white matter due to disturbed migration during development of human...

The normal laminar organisation of the cerebellar cortex is the result of the precisely controlled migration, differentiation and maturation of the neurons. Occasionally the migrating neurons lose their proper way of migration and form nests of grey matter in the improper place. The aim of this study was to investigate the morphological features of the lost neurons in the cerebellar white matter during development, with particular emphasis on their localisation, arrangement and differentiation. We analyzed 31 fetal and infantile brains, aged from 28 gestational weeks to 18 postnatal months. We observed different morphological patterns of cerebellar heterotopias. Clusters of grey matter reflecting the cerebellar cortical pattern with well-defined molecular layer and altered granular and Purkinje cells were most frequently observed. The compact heterotopias were composed of bands or whirls of spindle and round granule cells situated closely together, while Purkinje neurons were completely disorganised. The ectopic cortex in the white matter with a normal layered structure containing all the components of the cerebellar cortex was localised by the large vessels. Aggregations of Purkinje cells scattered in the white matter without accompanying granule cells were observed. The evaluation of the biological features of the misplaced cerebellar cortical components showed high activity of neurons.