Children with small head circumference are not necessarily suffering from brain dysplasia, there are physiological factors and pathological factors, physiological factors are mainly related to heredity, and pathological factors are mainly related to malnutrition, cerebral palsy, abnormal bone development and other factors. 1. Physiological factors: If one of the parents of a child has a small head circumference, it may be passed on to the next generation, causing the child to have a small head circumference, which is a normal physiological phenomenon. 2. Pathological factors: (1) Malnutrition: Infants may also suffer from malnutrition, which may lead to delayed development and affect the growth of head circumference, thus causing small head circumference. (2) Cerebral palsy: If the head circumference of a child is smaller than normal and accompanied by mental retardation, it is considered to be caused by diseases, such as acquired cerebral palsy. (3) Abnormal bone development: If the child has normal intelligence but the head circumference is small due to pathologic reasons, it may be due to abnormal bone development, which leads to early closure of the bone suture, at which time the brain develops normally, but the bone development can not be matched with the brain development. If a child has a small head circumference, after eliminating physiological factors, parents are advised to bring the child to the doctor in time to find out the cause and give targeted treatment.