Microcephalus (also called microcephaly)


Condition Description

Microcephaly (my-kro-SEF-ah-lee) is a condition in which the circumference of the head is smaller than normal because the brain does not grow at the expected rate. In this condition, the brain's small size will result in a head circumference that is less than 2 standard deviations below the average size for a child of that age.

Microcephalus (my-kro-SEF-ah-lus) is of two types. Primary microcephalus occurs with no identifiable cause as an inherited trait in families where many members are born with small head sizes. Secondary microcephalus occurs when the brain's growth is decreased because of conditions that can be identified: chromosomal anomaly such as Down syndrome, congenital infections with organisms such as the virus rubella, metabolic disorders, bacterial meningitis, or lack of oxygen early in life (called hypoxic-ischemic encephalopathy). A mother who uses drugs or alcohol during pregnancy can also have a child with microcephalus. Exposure to radiation or chemicals can also produce a small head size (and thus, small brain). This is especially the result of conditions that occur in the first two years of a child's life when the brain growth is most rapid.


The number of children with primary microcephalus is 1 in 40,000 live births, making this a rare condition. The prevalence of secondary microcephalus much higher, but it is hard to estimate since it results from multiple conditions.

Common Associated Conditions

In primary microcephalus the child may have no apparent associated symptoms. Secondary hydrocephalus may have many associated conditions, depending on the cause. For example, rubella syndrome is associated with intellectual disabilities, vision and hearing problems, and cognitive impairment. Failure to thrive in infants and toddlers, which itself is a description not a diagnosis, will generally affect the head growth. The majority of head growth occurs in the first 3 years of life, so any health condition that impairs overall nutrition in those critical years can affect head size.

It important to contrast microcephalus with a condition called craniosynostosis. Craniosynostosis is a condition in which the bones of the skull fuse too early, preventing the skull from growing properly; this bone fusion causes overlap of the skull bones, irregular head shape, and potentially, pressure on the brain. This occurs in the first year of life and is a reason that babies need frequent well-child examinations with palpation of the skull bones and head-size measurements. Craniosynostosis is quite easily corrected by surgery that opens the spaces between the skull bones so that the brain can grow and develop normally.

Short-term Treatment and Outcomes

There is no specific treatment for microcephaly except careful neurologic and developmental monitoring. The child's plan of care will focus on maximizing the child's strengths and minimizing the effects of related conditions, if any. Genetic counseling may be offered in situations where microcephalus is part of a syndrome with an inherited pattern.

Long-term Treatment and Outcomes

No specific treatment for microcephalus exists. The effects of the condition will become more apparent as the child grows. Maximizing the child's nutrition for maximum head growth, and providing optimum intellectual stimulation will be important. The outcome will be very unique to each child.

Common Complications

Complications depend on underlying causation of microcephaly. Since head size is an indication of brain growth, there will be a concern about overall intellectual development. Intellectual disabilities, delayed motor function and speech development, dwarfism or short stature, seizures, and hyperactivity are some of the related conditions. However, many children with small head size have normal intelligence.

Implications for Children's Development

Children with microcephalus may have normal or decreased cognitive function. Early intervention and special education may be needed to maximize the child's potential and provide support and appropriate services. No assumptions should be made based on appearance alone since children vary greatly in their function with this condition. Parents can benefit from learning more about microcephalus and connecting to other parents who have had similar experiences. Below are some useful online resources for parents and families.