Generally speaking, myelin development begins in infants at around 3-6 months after birth, and can often peak between the ages of 2-4 years, and can reach more than 80% of that of an adult in school-age children, that is, at the age of 6-7 years. The myelin sheath is an important landmark of myelinated nerves. Myelin actually consists of a membranous structure outside the axon of a nerve cell, made up of myelin cells, and its main function is to act as an insulator, preventing nerve impulses from interfering with the surrounding nerves. Also, myelinated nerves conduct significantly faster than unmyelinated nerves because they conduct in jumps. In addition, myelin sheaths allow damaged nerves to guide the regeneration of axons, so that normal development of myelin sheaths often signals the gradual refinement of the nervous system. If the myelin sheath is not sufficiently supplied with nutrients during development, or is affected by viral infections, exogenous factors, or toxins, the development of the myelin sheath can be impaired, resulting in delayed development of the nerves or corresponding brain functions, which can be characterized by typical changes in the imaging. Myelin dysplasia and delayed development can occur if affected by external factors such as drugs, poisoning, infections, and congenital diseases. There are certain changes in imaging and clinical symptoms that need to be treated in time.