Infant Toddler Development Training
Module 6, Lesson 4
Neurological conditions are those that affect the central and/or peripheral nervous system and other conditions that affect movement and muscles. Neurological conditions include disorders of development, brain malformations, neural tube defects (NTDs), seizures, movement disorders, spinal cord problems, and peripheral nerve problems.
A developmental disorder is a cognitive, communication, adaptive, motor, or social-emotional impairment resulting from a neurological, orthopedic, or other organic problem. Developmental delays, that are sometimes the result of a disorder, are often amenable to “catch-up” over time if an infant or toddler is provided with developmentally appropriate interventions. All children can benefit from early intervention supports and services regardless of the degree of disability or delay.
Brain malformations are a group of neurological conditions that can affect development in all domains. Brain malformations are described based on the context of normal embryological development. As structures develop in the embryo, various factors such as genetic predisposition will produce defects in the process. These defects will then result in abnormal structures.
The brain and spinal cord begin as a flat disk that folds in upon itself and then shuts like a zipper starting at the end that would be the head or neural fold at the cephalad end. This is the beginning of the brain. This forward or cephalad structure starts to fold in on itself and the structures enlarge and the cells multiply preferentially to form the cerebrum, cerebellum and brain stem regions of the brain.
There is a cavity formed inside the neural tube that becomes the ventricles and spinal cord. The fluid inside this structure nourishes the internal lining as the circulatory system develops. There is a remarkable magnitude of cellular proliferation and migration during early embryological development so that every organ system in the body develops. The cellular numbers peak at about five months gestation and then begin to gain in size and maturity. The nerve cells (tracts) begin to form protective sheaths called myelin that insulate the nerve tracts and act much like insulation on electrical wires so that short circuits do not occur. The dendrites, small nerve endings that make the connections between the cells, also proliferate until they reach their maximum number postnatally. Dendrites begin to prune themselves at about one year of age as cell functions are differentiated.
At the posterior end of the neural tube, the spinal cord structures develop and mesenchymal elements envelop them to form muscles. Neurons or nerve cells along the neural tube are also forming myelin sheaths.
Abnormalities (malformations) in brain structure have their origin in these early processes of embryological formation with the most significant problems resulting from interruptions or deviations from the typical processes somewhere in the second to fourth month of gestation.
Lissencephaly or "smooth brain" is one of the malformations. It is part of many different syndromes and at least one of these is caused by a gene defect. This results in a lack of convolutions or folds on the brain. Agyria is complete absence of folds.
Pachygyria is an abnormality of few, unusually broad gyri and is associated with an abnormally thick cortical plate. It is closely related to lissencephaly.
These defects are caused from migrational defects where the cells do not get to their designated places. If these defects occur in only a small portion of the brain there may be no noticeable problems, but if the defect covers a large portion of the brain there are often major developmental issues.
Significant brain malformations can be seen on imaging studies. Many other disorders of brain development may not be seen by standard imaging studies. However, they may be present and detected as they become manifest by their symptoms which often include moderate to severe retardation.
Besides these defects which can be detected with imaging studies (such as lissencephaly and pachygyria), other defects such as anencephaly (absence of most of the brain), Dandy-Walker malformations (agenesis of the 4th ventricle structures), absence of the corpus callosum, certain types of Arnold-Chiari malformations, porencephalic cysts occurring in the lateral ventricles, and hydrocephalus (water on the brain) can also be seen with imaging techniques. Cerebellar malformations, such as cysts, and abnormalities of the cerebellum, such as Arnold-Chiari, may also involve the brain stem. They may cause hydrocephalus, due to the obstruction of the spinal fluid circulating system, often at the level of the third and fourth ventricles of the brain.
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