|Head size in infants is measured using the frontaloccipital (from the front to back of the head) circumference (FOC). These measurements can then be plotted over time on a standard growth chart as part of your child's routine well child checkups. It is important to keep in mind that it is how your child's head is growing over time that is more important than any one point on his growth chart.
Microcephaly refers to a head circumference that is smaller than normal (and is more than 2-3 standard deviations below normal) and it correlates with having a brain that is also small. Most children with microcephaly, especially if they are otherwise growing and developing normally, will have normal intelligence and should continue to develop and meet regular age appropriate milestones. In these children, even though their head is small, it should grow normally and track parallel to the normal growth curves for head circumference, even though they are below the curve.
Head circumference growth rates are fastest in the newborn period and a child's head should normally growth at the following rates:
- 2 cm/month in the first three months
- 1 cm/month from four to six months
- 0.5 cm/month from six to twelve months
- 2 cm/year from twelve to twenty-four months
Causes of microcephaly are usually grouped into those that are considered to be primary, in which the brain didn't form properly, or secondary to a process that interfered with the growth of a normally developed brain.
Among the causes of primary microcephaly include microcephaly vera, which is a genetic cause of a small head size, which is noticed at birth. Children with this condition will have other family members with the same condition, and they may also be short, have seizures and have normal or mildly retarded intelligence. Other causes of primary microcephaly include chromosomal disorders, anencephaly (with an absent scalp and open skull), encephaloceles, agenesis of the Corpus Collosum, holoprosencephaly, and lissencephaly.
Children with secondary microcephaly had a normally developing brain, but had some condition or disorder that interfered with continued growth. These children usually have a normal head size at birth, with a later decrease in the rate of growth, which results in a small head size in later childhood.
Common causes of secondary microcephaly include intrauterine infections, especially cytomegalovirus infection (CMV), drug use during pregnancy, injuries around the time of birth (perinatal brain injuries), which are often accompanied by cerebral palsy, and chronic disease or malnutrition in infancy. Other infections, such as meningitis or encephalitis and metabolic disorders can also cause microcephaly. In children with failure to thrive, there has usually been a decrease in the child's weight and height before the head stops growing.
Craniosynostosis, a disorder in which the sutures of the skull become fused, can also cause microcephaly. In addition to their head being small, children with craniosynostosis usually also have an abnormally shaped head.
A cranial MRI is the usual test ordered to determine the cause of microcephaly. For children with a small head size, but who are otherwise growing and developing normally, testing may not be necessary. TORCH titers in the mother and child, which test for common intrauterine infections, including toxoplasmosis, rubella, cytomegalovirus, and herpes simplex virus may also be helpful. A karyotype may be done if a chromosomal disorder is suspected. Other testing may be directed at looking a metabolic disorder as the cause of your child's microcephaly.
Children with microcephaly and developmental delays should probably be evaluated by a Pediatric Neurologist and should be referred to an early childhood intervention program.
Microcephaly Internet Resources:
- eGroups Microcephaly discussion list: "This is a discussion list for parents of children (of any age) with Microcephaly and related developmental disabilities. Share stories about your kids ups and downs, get advice and support, or just have someone to 'listen'."