As the child’s brain develops, new developmental abilities arise. Skills in multiple domains are acquired concurrently. These domains include motor, sensory, language, cognitive, attention, social, and self-care skills. Development of any one or multiple domains may go awry in childhood, resulting in patterns of developmental impairments with clinical diagnostic features.

The fetal brain develops from the neural tube and prosencephalon. Neuronal precursors proliferate between 12 and 16 weeks of gestation. Neurons migrate to form the six-layered insideout cortex between 12 and 20 weeks gestational age. Subsequently (in fetal as well as years into postnatal brain development), organization of the multilayered cortex takes place, with dendritic arborization, synaptogenesis, pruning of synapses, and apoptosis. Glial cells proliferate, and the myelin-forming cells, oligodendrocytes, differentiate. Finally, myelination prenatally proceeds first in the brainstem and cerebellum. Myelination continues into young adulthood, with central sensory system pathways becoming myelinated before motor systems. Myelination of central cortical sites occurs, followed by the occipital and then frontotemporal poles. From early development into late adolescence, functional connectivity of neural networks is continuously modified.

Evaluation of children relies heavily on comparison of their developmental abilities relative to those of their peers. For this reason, adjustments for conceptual age and knowledge of typical developmental milestones are essential. Children’s early development proceeds in an orderly fashion in several areas, first with primitive reflexes and then more complex developmental processes (Tables 18.1 and 18.2). Much like in neurological examination of adults, children’s developmental milestones can be organized based on various domains. These include motor skills (both fine motor and gross motor), language abilities (both receptive and expressive), socialization skills, cognitive abilities, and executive function. Significant delays in acquisition of these milestones can occur in any of the domains or a combination of domains. For example, a child may have language delay only, delays in fine or gross motor skills, or a combination of language and motor delay. These delays assume an otherwise normal neurological examination, without evidence of focal or lateralizing neurological signs indicating a possible underlying structural etiology. Regression warrants neurological consultation for metabolic disorder or neurodegenerative disorder, such as leukodystrophy or gray matter disorder.