Normal brain development.
| Stage 1: Dorsal induction: Formation and closure of the neural tube |
| - Occurs at 3-5 weeks of gestation |
| - Three phases: neurulation, canalization, retrogressive differentiation |
| - Malformations of dorsal induction: anencephaly, exencephaly, cephaloceles, Arnold-Chiari malformations and spinal dysraphism |
| Stage 2: Ventral induction: Formation of the brain segments and face |
| - Occurs at 5-10 weeks of gestation |
| -Three vesicles (prosencephalon, mesencephalon, and rhombencephalon) form the cerebral hemispheres/thalamus, midbrain, and cerebellum/brain stem respectively. |
| - Development of face |
| - Malformations of ventral induction: holoprosencephaly, Dandy-Walker malformation, cerebellar hypoplasia/dysplasia, Joubert syndrome, rhombencephalosynapsis, optic dysplasia, pituitary abnormalities and facial anomalies. |
| Stage 3: Migration and histogenesis |
| - Occurs at 2-5 months of gestation |
| - Neuronal migration from germinal matrix to the cortex |
| - Cortical organization |
| - Failure of migration: abnormal gyration patterns (heterotopias, simplified gyria, polymicrogyria), schizencephaly, corpus callosum agenesis/hypoplasia. |
| - Failure of histogenesis: aqueductal stenosis, arachnoid cysts, megalencephaly, micoencephaly, neurocutaneous syndromes, congenital vascular malformation, and congenital neoplasms of the brain. |
| Stage 4: Myelination |
| - Begins at 6 months of gestation; matures by 3 years. |
| - Myelination proceeds from caudal to rostral, from posterior to anterior regions; and from central to peripheral locations. |
| - Failure: leukodystrophies, metabolic disorders. |