Megalencephaly (Macrencephaly)

What is megalencephaly?

Megalencephaly (also known as macrencephaly) is a condition present at birth where your child’s brain is abnormally large. The brain itself is too heavy — it weighs more than expected for your child’s age and body size.

An early sign of megalencephaly may be an unusually large head. Your child may not be able to wear hats or headbands comfortably, as clothing and accessory sizes for their age may be too small.

A large brain may affect your child’s development and cause delays. It could take your child longer than expected to say their first words, crawl and walk, for example.

Megalencephaly often happens with other conditions. A genetic variation usually causes it.

What are the types of megalencephaly?

There are three main types of megalencephaly:

• Primary megalencephaly (benign familial megalencephaly or idiopathic megalencephaly): Children have a large brain but don’t have other symptoms or neurological problems. Usually, in these cases, one or both parents also have an increased head size. Your child’s head size may increase until they’re about 18 months old before it stabilizes.
• Metabolic megalencephaly: Inborn errors of metabolism (a group of genetic conditions that affect how your body processes food) cause megalencephaly.
• Anatomic megalencephaly: A gene change (mutation) that affects the development of your child’s nervous system (neurodevelopmental disorder) causes this type. Megalencephaly usually happens as a symptom of an underlying condition.

Your child’s healthcare provider may classify the type of megalencephaly based on what side of their brain (hemisphere) is larger than expected:

• Hemimegalencephaly (unilateral megalencephaly): Hemimegalencephaly means only one side of the brain is larger than the other.
• Bilateral megalencephaly: Bilateral megalencephaly affects both sides of the brain. Bilateral means “two sides.”

What are the signs and symptoms of megalencephaly?

Symptoms of megalencephaly may include:

• Developmental delays.
• Seizures (epilepsy).
• Neurological problems (abnormal functioning of the brain and spinal cord).

Sometimes, megalencephaly happens on its own without any symptoms. Other times, it comes along with other neurological problems and birth defects. In these cases, the other syndrome or condition may cause megalencephaly.

Other signs and symptoms of megalencephaly may include:

• A large or asymmetrical head.
• Intellectual disability.
• Difficulty with movement and balance.
• Strong or weak muscle tone.
• Vision changes.

What causes megalencephaly?

Megalencephaly happens due to an error in how your child’s brain makes brain cells. A genetic variation usually causes this to happen.

Neuron proliferation is your body’s process of making new neurons or nerve cells. Typically, your body regulates that process to produce the right number of cells at the right time. But with megalencephaly, your child’s body produces too many cells or they don’t migrate properly. This may happen as they develop or as part of another condition.

What other conditions happen with megalencephaly?

Megalencephaly can occur with many other conditions and syndromes, depending on the type and genetic origin.

Conditions associated with anatomic megalencephaly

Anatomic megalencephaly is typically a symptom of the following conditions:

• Achondroplasia.
• Bannayan-Riley-Ruvalcaba syndrome.
• Greig cephalo-polysyndactyly syndrome.
• Opitz–Kaveggia syndrome.
• Pretzel syndrome.
• Simpson-Golabi-Behmel syndrome.
• Sotos syndrome.
• Weaver syndrome.

Conditions associated with metabolic megalencephaly

Your child may have megalencephaly combined with inborn errors of metabolism — problems with how their body breaks down food and uses energy. These conditions may include:

• Abnormalities with organic acids (organic acidurias).
• Metabolic encephalopathies, such as Canavan disease and Alexander disease.
• Lysosomal storage diseases, including Tay-Sachs disease and Sandhoff disease.

What are the risk factors for megalencephaly?

Megalencephaly can affect any child. It’s more common among people assigned male at birth. In some cases, you can inherit it from your biological family, or it can happen randomly (sporadically).

How is megalencephaly diagnosed?

Your child’s healthcare provider may suspect megalencephaly after a physical exam and testing. During the exam, their provider will measure your child’s head with a measuring tape. They’ll check where your child’s measurement is by comparing it to the average for their age, sex and height.

Their provider may order imaging tests, like an MRI. This allows them to see your child’s brain and look for any abnormalities.

If they suspect an underlying condition with megalencephaly, your child may undergo additional testing to confirm a diagnosis. Additional tests may include:

• Blood tests.
• Urine tests.
• Genetic test.

When is megalencephaly diagnosed?

Sometimes, parents and healthcare providers notice that a baby has a large head at birth or within their first few months. Megalencephaly may develop as your child grows, usually during infancy and early childhood.

Providers may detect hemimegalencephaly (where only one side of your child’s brain is large) during a pregnancy ultrasound.

How do you treat megalencephaly?

There isn’t a cure for megalencephaly, but treatment options are available to help your child manage symptoms. Their healthcare provider may recommend the following based on what symptoms they experience:

• Taking antiseizure medications or undergoing epilepsy surgery for seizures.
• Participating in vision therapy, physical therapy, occupational therapy or speech therapy.
• Enrolling in early intervention or special education courses at school.

Who is on my child’s care team?

Your child will have a robust care team to help them manage megalencephaly symptoms. Your child’s care team may include:

• Pediatricians.
• Neurologists.
• Neurosurgeons.
• Developmental specialists.
• Speech, occupational and physical therapists.

Can megalencephaly be prevented?

There’s no known way to prevent megalencephaly. If you suspect or know this condition runs in your biological family history, you can speak with a genetic counselor. They can help you assess your risk of having a child with megalencephaly.

What’s the outlook for megalencephaly?

Your child’s outlook varies based on many factors, like the severity of their symptoms and the underlying cause. Your child may only have a larger head and no additional symptoms. Or symptoms may affect your child’s development. For example, they may need additional help completing their daily routine or learning support at school.

Your child’s healthcare provider will give you the most accurate information on their outlook, as it’s as unique as they are.

What’s the life expectancy for megalencephaly?

Mild cases of megalencephaly may not affect your child’s life expectancy. However, depending on the underlying cause, like if megalencephaly happens alongside another condition, your child’s life expectancy may be shorter. Severe symptoms, like seizures, may affect your child’s outlook. Your healthcare provider can give you information based on your child’s situation and what you can expect as they grow.

When should I see a healthcare provider?

Let your child’s healthcare provider know if you notice any new or worsening symptoms of megalencephaly. It helps to keep track of your child’s development and to let their provider know if they’re not on track to meet those, like sitting up on their own or speaking their first words.

Contact emergency services if your child has a seizure for the first time.

What questions should I ask my healthcare provider?

If your child receives a megalencephaly diagnosis, ask their provider:

• What type of megalencephaly does my child have?
• Does my child have other conditions?
• What kind of treatment will work best?
• What’s the outlook for my child?
• How can I help my child at home?

What is the difference between macrocephaly and megalencephaly??

Macrocephaly, also called megacephaly or megalocephaly, is a large head size. In macrocephaly, a child may have a large head but not necessarily any structural problems.

Megalencephaly (a large brain) can cause macrocephaly. However, macrocephaly can also develop because of fluid buildup in your brain (hydrocephalus) or increased pressure within your skull.

What is megalencephaly-capillary malformation (MCAP)?

Megalencephaly-capillary malformation (MCAP) is a rare condition where there’s tissue overgrowth of the following:

• Skin.
• Blood vessels.
• Connective tissue.
• Brain.

Usually, healthcare providers diagnose MCAP when a baby is born. Children born with MCAP have:

• An enlarged brain (megalencephaly).
• A large head size (macrocephaly).
• Capillary malformations (abnormal tiny blood vessels).

What is megalencephaly-polymicrogyria-polydactyly-hydrocephalus (MPPH)?

Megalencephaly-polymicrogyria-polydactyly-hydrocephalus (MPPH) is a condition that affects how your child’s brain develops. They may have a large brain size (megalencephaly) that continues to grow rapidly during their first two years. It can affect your child’s development, movement and intelligence.