DESCRIPTION
Children with megalencephaly have a brain that is larger than average. This is determined with a comparison to other children of the same age and sex.
Various conditions can cause an increase in the number or size of brain cells. This may result in a larger brain. Because of the large brain, children with megalencephaly also have a large head.
Head circumference is the total distance around the head. It is usually measured with a tape measure at physical exams. In megalencephaly, a child’s head size is above the 97th percentile. In other words, it measures larger than 97% or more of other children’s heads. This comparison is made with standard size charts. The standards are provided by organizations like the CDC. Comparisons may also be made to parents’ or siblings’ head sizes.
Megalencephaly affects more males than females.
Macrocephaly Vs. Megalencephaly
It is important to differentiate between macrocephaly and megalencephaly.
Macrocephaly refers to an increased head circumference. It may have various causes. They can include:
- Abnormalities of the skull’s bone structures
- An increase of fluid collection in the brain or surrounding the brain
- An enlargement of the brain (megalencephaly)
Having macrocephaly does not necessarily mean a child has a brain abnormality. It only indicates a large head. The brain may be normal. Some families have a tendency for larger head size in children and adults, who may be otherwise normal neurologically or have no other symptoms.
Megalencephaly refers to an increased brain size. It reflects the growth of abnormal brain structures. This can happen at various steps of brain development. Megalencephaly is more severe than macrocephaly. It is more likely to include:
- Developmental delays
- Learning delays
- Seizures
- Other neurologic symptoms
Not all people with a larger head have an enlarged brain. However, most people with an enlarged brain do have a larger head, too.
SIGNS AND SYMPTOMS
Signs
The primary sign of this condition is a large head. The head may be large at birth. Or it may become larger as a child grows.
Measuring the head:
- Ultrasound. This may be used before birth or after birth.
- Tape measure. This may be used after birth or at childhood doctor’s visits.
Symptoms
This condition may look different in different cases:
- Large head only. Sometimes, a large head is the only symptom.
- Developmental delays. Most children with this condition have delays. Intellectual disabilities may appear as they grow older.
- Other organs affected. This condition may be part of an underlying genetic syndrome. The underlying syndrome can affect organ systems besides the brain.
In addition to the above, children with this condition may have:
- Seizures
- Movement issues
- Balance issues
- High muscle tone
- Low muscle tone
- Feeding issues
- Breathing issues
- Dark- or light-colored spots on the skin
- Vision problems
CAUSES
Most causes of this condition are genetic. Genetic causes can occur for different reasons. They may be:
- Inherited from parents
- Due to a new change in a child’s gene
Specific genetic causes for this condition include:
Neurocutaneous disorders
Metabolic disorders
Metabolic disorders may be inherited or due to new mutations. They cause problems with how chemical reactions happen in the body. They can affect how the body produces energy. These disorders may lead to a buildup of toxins in brain cells. This can make brain cells larger than normal. Then, brain cells may not function properly. Abnormal brain development is sometimes the result.
OUTLOOK
Prognosis varies greatly. It depends on:
- The severity of the condition
- The underlying cause of the condition
Severe Cases
In severe cases:
- Lifespan may be shortened. Lifespan may be shortened due to seizures, feeding or swallowing issues, or other problems. Some causes of megalencephaly, particularly metabolic causes, can lead to a shorter lifespan due to progressive brain dysfunction.
- Disability may be significant. Significant intellectual disability is common in this condition. Children may need help with everyday tasks as they grow up.
- Education may be more challenging. Children may need help in school. They may need special education support or therapy.
Milder Cases
In milder cases:
- Lifespan may be normal. Lifespan may be normal.
- Disability may be milder. Children may have only mild delays. They may be able to perform everyday tasks independently.
- Education may be less challenging. Children may only need a small amount of help in school.
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