The embryonic development of the nervous system is an extremely complex process that can be disrupted due to genetic defects, intrauterine infections (cytomegalovirus, herpes simplex virus, rubella, HIV), intoxication (alcohol, some narcotic drugs, medications), radiation exposure, etc.
The anomalies that occur in this case largely depend on the phase of development of the nervous system, i.e., the stage of formation of the neural tube (3.5–4 weeks), the stage of formation of cerebral vesicles (4–5 weeks), the stage of formation of the cerebral cortex (6–8 weeks), etc. As a result, various defects in the development of the brain and spinal cord, skull and spine can develop. These defects can occur in isolation or in various combinations.