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Authors: Margaret Means, MDSonika Agarwal, MBBS, MD, Children’s Hospital of Philadelphia 

Reviewed: July 2021 


In microcephaly, a child’s head is significantly small for that child’s age and sex. This is usually due to abnormal brain development. The brain may have developed differently during pregnancy or after birth.  

This condition can have many different genetic or environmental causes. Children will usually have developmental delays. They may have other neurological issues, too. Seizures are one example.  

A diagnosis is made by: 

  • Measuring the head  
  • Looking at images of the brain 

Treatment usually includes several therapies. The therapies can help with delays. They can help with other symptoms, too. 


Disorder Overview


In the United States, about 1 in every 800–5,000 babies are born with microcephaly. There is a wide range due to different causes at different ages. It is also because of a range of severities (mild or borderline, moderate and severe). 

Children with microcephaly have a head circumference (distance around the head) at or below the third percentile for head growth. In other words, they will have a smaller head than 97% or more of children of their age and sex.  

A healthcare provider will measure the head circumference during the physical examination. This is compared to the standard charts provided by organizations like the CDC (Center for Disease Control). These measurements are also compared to the  measurements for parents or siblings. 

Symptoms can range from mild to severe. In general, the smaller the head size, the more severe the symptoms. There are a number of different causes, as described below: 

  • Lack of normal brain growth 
  • Poor brain development before or after birth 
  • Exposures to infections, toxins, drugs and alcohol 
  • Interruption to flow of oxygen and or blood supply to the brain during development 

There may also be unknown reasons. 

microcephaly 1



Diagnosis is made by measuring the head.

This may be done with: 


Used before and/or after birth. 

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Tape measure

Used after birth and at doctor visit as the child grows. 

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Differences in how a child’s brain has developed can be seen with brain imaging.  

Magnetic resonance imaging (MRI) is often used for this imaging.


The two symptoms present in about half of all patients are: 

  • Developmental delay  
  • Cognitive disability 

These symptoms can range from mild to severe. It depends on the cause and severity of the microcephaly. 

Other possible symptoms include issues with: 

  • Seizures 
  • Movement  
  • Balance  
  • High muscle tone 
  • Low muscle tone 
  • Feeding  
  • Growing or gaining weight 
  • Hearing  
  • Vision 

Sometimes, microcephaly is part of an underlying genetic syndrome in which other organ systems have problems. 

Sometimes, a small head is the only sign of microcephaly.  

Holoprosencephaly 1


There are many possible causes.

Genetic Causes

Genetic causes can occur for different reasons. They may be:

  • Inherited from parents
  • Due to a new change in a gene in the child

Examples of genetic causes include:

Chromosome disorders

These disorders are usually due to a missing part of, or duplication of a part of, or an extra chromosome. One example is trisomy 21, or Down syndrome. 

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Isolated primary microcephaly

This is an inherited formPrimary microcephaly is inherited from the child’s parents. Obtaining the parents and siblings head circumference may be very helpful in making this diagnosis. 

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Metabolic disorders

Metabolic disorders may be inherited or due to new mutations. They cause an abnormality of proteins that control functions in the brain and body, resulting in either a build-up of toxic substances in the brain and other tissues or an absence of an important function in the brain. 

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Structural brain malformations

Sometimes, the brain structure is abnormal during the developmental process in the womb. It can be caused by many factors such as genetic, infectious, metabolic issues and exposures. These include abnormal structural developmental diagnoses such as: holoprosencephaly, polymicrogyria, schizencephaly, lissencephaly, neural tube defects and others 

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Syndromic microcephaly

Numerous genetic syndromes have microcephaly as an associated sign. 

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Acquired Causes 

Acquired causes are causes not related to genetics.  

During Pregnancy 

Microcephaly can be caused by issues affecting a mother during pregnancy.

They include: 

  • High blood pressure 
  • Untreated diabetes
  • Problems with the placenta
  • Malnutrition 
  • Infections, such as: Toxoplasmosis, Syphilis, Varicella Zoster, Parvovirus B-19, Rubella, Cytomegalovirus (CMV), Herpes virus, Zika virus 
  • Heavy alcohol or drug use, other toxins 
microcephaly 3

Other Acquired Causes 

Some other causes that can arise include: 

Hypoxic ischemic brain injury

Due to lack of oxygen or blood flow.  Learn more about hypoxic ischemic brain injuries.

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Hemorrhagic brain injury

 Due to bleeding in the brain.  

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Other brain injury

Stroke is an example, or trauma to the developing brain. 

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Severe lack of nutrition after birth.  

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Early fusion of the skull

This can inhibit brain growth. It is called craniosynostosis. 

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Sometimes, the exact cause cannot be determined.  


Clinical Exam 

Diagnosis may involve measuring a child’s head. Doctors measure the circumference, or distance around, a child’s head. A child’s head circumference is typically measured at each doctor’s visit. 

Brain Imaging 

Pictures taken of the brain can provide information to doctors. The pictures can show differences in how a child’s brain developed. Two types of imaging are most common: 


Used prior to birth. 

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Magnetic resonance imaging (MRI)

Used after birth.  

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Blood Testing 

Tests for infections may be used to look for an underlying cause, such as CMV (cytomegalovirus), toxoplasma, Zika virus. 

Genetic Testing 

Tests for changes in the child’s genes may reveal a likely cause. Parents may then also be tested. Testing parents can show whether a genetic change is inherited or new in the patient. It can help determine the risk of this condition appearing in future pregnancies. A genetic counselor can help interpret test results. 

Genetic tests may include: 

A chromosomal microarray

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A microcephaly panel

This is a panel of genes commonly associated with the condition. 

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Whole exome sequencing

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Treatment usually focuses on symptoms. If the condition is severe, a child may need long-term treatment. 


Various therapies may be needed. Therapies can include: 

  • Physical therapy 
  • Occupational therapy  
  • Speech therapy 
  • Feeding therapy  

Seizure Treatment 

Some patients have seizures. In these cases, antiseizure medicine may be needed.  

Seizures in patients with microcephaly can be difficult to control. However, there are multiple medicines available. Sometimes, no medicine can control the seizures. In these cases, there are alternatives to consider: 

  • Dietary options 
  • Surgical options 


Prognosis varies greatly. It depends on: 

  • Severity 
  • Underlying cause 

In general, the more severe the condition (the smaller the child’s head), the more severe the symptoms. 

Severe Cases 

In severe cases: 


Lifespan may be shortened due to seizures, feeding or swallowing issues, or other problems.  

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Significant intellectual disability is likelyChildren may need help with everyday tasks as they grow up.  

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Children will need help in school. Parents can request that the child be evaluated and have an “IEP” or individualized educational plan to assist with any learning disabilities. 

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Milder Cases 

In milder cases: 


Children may have only mild delays. They may be able to perform everyday tasks independently. 

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Lifespan may be normal. 

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Children may only need a small amount of help in school. 

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ClinicalTrials.gov for Microcephaly are clinical trials that are recruiting or will be recruiting. Updates are made daily, so you are encouraged to check back frequently.  

ClinicalTrials.gov is a database of privately and publicly funded clinical studies conducted around the world. This is a resource provided by the U.S. National Library of Medicine (NLM), which is an institute within the National Institutes of Health (NIH). Listing a study does not mean it has been evaluated by the U.S. Federal Government. Please read the NLM disclaimer for details.  

Before participating in a study, you are encouraged to talk to your health care provider and learn about the risks and potential benefits. 

The information in the CNF Child Neurology Disorder Directory is not intended to provide diagnosis, treatment, or medical advice and should not be considered a substitute for advice from a healthcare professional. Content provided is for informational purposes only.  CNF is not responsible for actions taken based on the information included on this webpage. Please consult with a physician or other healthcare professional regarding any medical or health related diagnosis or treatment options. 


Swaiman KF. Swaiman’s Pediatric Neurology: Principles and Practice. Edinburgh: Elsevier; 2018. Ch 28: Disorders of Brain Size. p. 208-212.  

Pina-Garza JE. Fenichel’s Clinical Pediatric Neurology. London: Elsevier Saunders; 2013. Ch 18: Disorders of Cranial Volume and Shape. p. 358-359.  

Microcephaly. Mayo Clinic. Published June 25, 2020. https://www.mayoclinic.org/diseases-conditions/microcephaly/symptoms-causes/syc-20375051  

Facts about Microcephaly. Centers for Disease Control and Prevention. Published October 23, 2020. https://www.cdc.gov/ncbddd/birthdefects/microcephaly.html    

Ashwal S, Michelson D, Plawner L, Dobyns WB. Practice parameter: Evaluation of the child with microcephaly (an evidence-based review): Report of the quality standards subcommittee of the American Academy of Neurology and the Practice Committee of the Child Neurology Society. Neurology. 2009 Sep 15;73(11):887–97. PMID: 19752457; https://doi.org/10.1212/WNL.0b013e3181b783f7  

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