The medical term used to describe an enlarged brain size is megalencephaly (also known as macroencephaly). While this condition may occur on its own, sometimes, people develop due to certain genetic conditions. Usually, children who experience megalencephaly have the following symptoms. These include seizures and developmental delays. Unfortunately, there is no way to cure this condition. That’s why the treatment goal is to relieve the symptoms, prevent life-threatening complications, and improve your quality of life.
In other words, in people with megalencephaly, the brain is too heavy for the child’s age and body size. One of the first signs of megalencephaly is unusual large size in children. For instance, a child may be unable to wear hats or headbands comfortably. Furthermore, an unusually large brain may negatively affect the child’s development and cause delays. One example is a child that difficulty beginning to walk, crawl, or say their first word.
Types of Megalencephaly
Healthcare professionals have divided megalencephaly into 3 categories. These include:
- Primary megalencephaly (benign familial megalencephaly or also known as idiopathic megalencephaly) – The children with this type of megalencephaly have an enlarged brain but without other symptoms or neurological problems. In such cases, one or both parents also have an increased head size. Usually, the head grows until 18 months of age and then stabilizes.
- Metabolic megalencephaly – This type is often caused by inborn errors of metabolism. It means a group of genetic disorders that negatively affect the body’s ability to process food.
- Anatomic megalencephaly – The cause of this type of megalencephaly is a genetic mutation that impacts the development of your child’s nervous system (neurodevelopmental disorder).
Sometimes, doctors may classify this condition based on which side of the child’s brain (hemisphere) is larger. These include:
- Hemimegalencephaly (unilateral megalencephaly) – In such cases, only one side of the brain is enlarged.
- Bilateral megalencephaly – This type occurs when both hemispheres of the brain are enlarged.
Symptoms
While the primary symptoms of megalencephaly are seizures, developmental delays, and neurological problems (abnormal function of the brain and spinal cord), it may also cause other symptoms. Sometimes, people do not experience any symptoms. Check below for other symptoms of megalencephaly:
- Strong or weak muscle tone
- Problems with balance, coordination, and movement
- Large or asymmetrical head
- Vision changes (such as blurred or double vision)
- Intellectual disability
If you notice that your child experiences any of the previous symptoms, immediately contact your healthcare professional. Otherwise, it may lead to serious complications (such as permanent damage to the brain).
Causes and Risk Factors
This condition results from an error in how the child’s brain produces brain cells. In other words, megalencephaly happens due to a genetic mutation. The process by which the brain generates new neurons, or nerve cells, is called neuron proliferation. In normal circumstances, the body regulates this process to produce enough cells at the right time. However, in people with megalencephaly, the body produces too many cells, and they do not migrate properly. While this condition may occur on its own, sometimes it happens as a complication of another disease.
Healthcare professionals have also identified some factors that may elevate your risk of developing megalencephaly. These include:
- Sex – While anyone may develop this condition, it often affects males more commonly than females.
- Family history – If you have a sibling or parent with megalencephaly, the risk of developing it significantly increases.
- Genetic mutations and overgrowth syndromes – Most of the time, megalencephaly occurs randomly. However, the following genetic disorders may also contribute to this disease. For example, Beckwith-Wiedemann syndrome, neurofibromatosis, tuberous sclerosis, Sotos syndrome, and others.
- Metabolic disorders – There are some disorders that can cause toxic metabolic buildup in the brain. For example, Alexander disease, Canavan disease, lysosomal storage disease, and others.
- Environmental factors
- Congenital and developmental factors – In some cases, megalencephaly is associated with certain conditions that negatively affect the cerebrospinal fluid (such as malformation of cortical development).
What Other Disorders Happen with Megalencephaly?
People with megalencephaly may also experience other conditions, but it depends on the type and genetic origin. Examples include:
Conditions often associated with anatomic megalencephaly include the following conditions. For example:
- Pretzel syndrome
- Simpson-Golabi-Behmel syndrome
- Sotos syndrome
- Weaver syndrome
- Greig cephalo-polysyndactyly syndrome
- Achondroplasia
- Opitz-Kaveggia syndrome
- Bennayan-Riley-Ruvalcaba syndrome
Sometimes, your child has this disease along with other inborn errors of metabolism. The following conditions often affect the body’s ability to process foods. Examples include abnormalities with organic acids, metabolic encephalopathies, and lysosomal storage disease (including Tay-Sachs disease, Sandhoff disease, and others).
What Happens if Megalencephaly is Left Untreated?
Almost everyone who develops megalencephaly will experience complications. Check some examples below:
- Epilepsy – About 50% of people with associated syndromes will develop recurrent seizures in early childhood.
- Developmental delays – This complication ranges from mild to severe intellectual disability and cognitive impairment.
- Motor problems – These include poor coordination, high or low muscle tone (spasticity or hypotonia), partial paralysis, and others.
- Oromotor dysfunction – For example, dysphagia (problems with swallowing), profuse drooling, and speech delays.
- Hydrocephalus (fluid buildup in the brain)
- Cerebellar tonsillar herniation
- Segmental overgrowth
- Skin/vascular malformations
- Eye problems (such as cataracts, glaucoma, optic nerve atrophy)
The previous list does not contain all possible complications of megalencephaly, but you can consult with your doctor about measures to reduce the risk or even prevent them.
How to Prevent Megalencephaly?
Unfortunately, there is no way to prevent or reduce the risk of developing this condition. However, you can perform a genetic test before pregnancy to make sure you do not have the abnormal gene that causes megalencephaly. In general, it is very important to understand the risks of having children with this disorder.
Diagnosis
Like many other conditions, the diagnosis of megalencephaly starts with a physical examination in which doctors will check your child for irregularities associated with this condition. They may also ask some questions about symptoms and family history to gather more information about your child’s disease. However, to confirm or rule out megalencephaly, doctors often perform the following tests. Examples include:
- Blood tests
- Urine tests (also called urinalysis)
- Genetic tests
- Imaging tests – Sometimes, doctors may perform an imaging test to get detailed images of the brain and surrounding tissues. Usually, they perform an MRI (magnetic resonance imaging) scan or a CT (computed tomography) scan.
Treatment
There is no way to cure megalencephaly. That’s why the treatment goal is to relieve the symptoms, prevent serious complications, and improve your child’s quality of life. Usually, the treatments for people with megalencephaly include the following options. For example:
- Antiseizure medicines or epilepsy surgery for seizures
- Vision, physical, occupational, and speech therapies
- Special education courses at school
Megalencephaly may negatively affect multiple body systems. It makes your child need a healthcare team to treat the condition. These include pediatricians, neurologists, neurosurgeons, developmental specialists, and others.
Frequently Asked Questions
When is megalencephaly diagnosed?
While sometimes this condition can be detected during pregnancy on an ultrasound, some people may experience the first symptoms of megalencephaly during infancy or early childhood.
What is the life expectancy for megalencephaly?
Mild forms of megalencephaly do not need treatment and do not affect your child’s life expectancy. If it occurs along with other genetic disorders or serious complications, the same life expectancy may be shorter. Usually, doctors can give you information about your child’s lifespan based on the symptoms and other factors.
What is the difference between macrocephaly and megalencephaly?
While both conditions can cause similar symptoms, there are some differences between them. For instance, people with macrocephaly may have a large head, but without any structural changes. In people with megalencephaly, the brain becomes enlarged. If you have additional questions, ask your healthcare provider.
