Is One Side of Your Baby's Brain Too Big? Here is What You Need to Know About Hemimegalencephaly

Are you feeling worried about your baby's head shape or the seizures they keep having? Sometimes, these signs point to a very rare medical condition. That condition is called hemimegalencephaly. Even though the name sounds complicated, we can break it down into simple terms.

Finding out your child has a rare brain condition can feel overwhelming. You are not alone in this journey, and understanding the condition helps you make informed choices. Let us walk through what hemimegalencephaly means, what to look for, and how doctors treat it.

What Is Hemimegalencephaly?

Simply put, hemimegalencephaly means that one side of your child's brain is much larger than the other side. Think of our brain as having a left side and a right side. In this condition, one side grows way too much. Sometimes this extra growth affects just a small part of that side, or it can affect the whole half.

When one side of the brain grows this way, other changes happen inside. For example, your baby might have:

• Brain cells that did not form in the right pattern, or an outer brain layer that is misformed.
• A missing or poorly formed band of tissue that connects the two halves of the brain.
• Enlarged fluid-filled spaces inside the affected side of the brain.

Because the brain parts did not form correctly, seizures happen often. Doctors call this epilepsy. Usually, regular seizure medicines do not control these seizures well. If medicine fails, many children need brain surgery to help stop the seizures.

Are There Different Types of Hemimegalencephaly?

Yes, doctors group this condition into a few main types:

• Isolated hemimegalencephaly: This type affects only the outer layer of the brain. It does not affect the skin or other organs.
• Syndromic hemimegalencephaly: This type affects the brain as well as the skin and other organs. Skin marks might show up months or even years after birth. Also, one side of the body may grow larger than the other side.
• Total hemimegalencephaly: In this type, the lower part of the brain and sometimes the brainstem also grow larger. This can happen on its own or as part of a syndrome.

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What Are the Signs and Symptoms?

The first sign you might notice is that your little baby starts having seizures. These usually come as focal seizures that affect only one side of the body. You might see one side of your baby's body shaking or twitching.

Other signs and symptoms include:

• An unusually large head size.
• An uneven or asymmetrical head shape.
• Trouble with movement, such as walking or running.
• Weakness or lack of strength on one side of the body.
• Delays in reaching growth milestones, like talking, playing, or learning.
• Vision problems, such as losing half of your normal viewing range.

What Causes Hemimegalencephaly?

To be honest, doctors and scientists still do not know the exact cause of this condition. Some experts believe it happens because of a genetic change in the baby's DNA. However, this is not something passed down from parents. You did not inherit it and pass it to your child.

Most of the time, a random, sudden change happens in one of the genes that helps build the brain during the third week of pregnancy. Please remember that nothing you did during pregnancy caused this. This is not your fault, and it is not the father's fault either.

What Are the Risk Factors?

Hemimegalencephaly can sometimes happen along with other genetic conditions. This means children with certain syndromes have a higher chance of developing hemimegalencephaly:

• Epidermal nevus syndrome.
• Klippel-Trenaunay syndrome.
• McCune-Albright syndrome.
• Neurofibromatosis Type 1.
• CLOVES syndrome.
• Proteus syndrome.
• Hypomelanosis of Ito.

How Do Doctors Diagnose Hemimegalencephaly?

To make a sure diagnosis, your child's doctor will examine your child and ask about their health history. Then, they will likely order specific tests:

• A brain MRI scan to view the structure of the brain.
• An EEG test to check the electrical activity of the brain.

With modern technology, doctors can sometimes spot this condition before the baby is born. They use a special fetal MRI scan to look at the baby's brain while still in the womb.

How Do Doctors Treat It?

The main goal of treatment for hemimegalencephaly is to control seizures. These seizures can start very early in life, and they are often very hard to control with medicine alone.

Seizures can cause different issues. More importantly, seizures that start in early babyhood can seriously hurt a growing brain. Uncontrolled seizures harm normal learning and brain growth. Because of this, stopping the seizures as soon as possible is very important.

Treatment starts with anti-seizure medicines. Some children manage their seizures with these drugs for a long time. However, many children develop drug-resistant epilepsy. When medicine fails, doctors perform a surgery called a hemispherectomy. This surgery removes or disconnects the affected side of the brain.

Surgeons may perform a functional hemispherectomy. In this procedure, the surgeon cuts the nerve fibers connecting the two sides of the brain, but they may leave the large brain tissue inside the head. In an anatomic hemispherectomy, the surgeon separates and completely removes the abnormal brain half. A specialized neurosurgeon who focuses on epilepsy surgery should perform this procedure.

Is Hemispherectomy a Difficult Surgery?

To be honest, a hemispherectomy is a very complex brain surgery. Hemimegalencephaly makes this surgery even harder for several reasons.

First, the blood vessels inside the brain often form in unusual ways. Because of this, finding and cutting them during surgery is difficult, which can lead to heavy bleeding.

Also, because the whole brain is formed differently, surgeons miss normal landmarks used to guide them. Also, infants and young children can lose a lot of blood during this surgery. Doctors must watch them very carefully and give blood transfusions as needed.

Therefore, having an experienced medical team perform this surgery is vital. Choosing a hospital that often performs hemispherectomy surgeries for infants with hemimegalencephaly keeps your child safe.

What Is the Outlook (Prognosis)?

Your child's outlook depends greatly on how well doctors can control the seizures. It also depends on whether the brain growth issue affects one side or both sides.

Hemimegalencephaly affects every child differently. This means results vary quite a bit from one child to another.

• Many children have some level of intellectual disability.
• Some children whose seizures are well controlled reach a near-normal intelligence level.
• Other children face major challenges with walking, talking, and learning.

Almost every child with hemimegalencephaly has some weakness on one side of the body. This is a type of cerebral palsy. This weakness might be mild in some children and severe in others. Some children lose half of their visual field. While many children learn to walk and talk, others do not. Some children need special feeding tubes. This others eat normally.

Recent studies show that after surgery:

• 68% of children stop having seizures completely.
• 43% of children achieve a normal or mildly delayed intellectual level.
• 26% of children learn to speak at an age-appropriate level.
• 21% of children gain good reading skills.

Can You Prevent Hemimegalencephaly?

Because scientists do not know the exact cause of this condition, doctors have no way to prevent it.

How Do You Care for a Child With This Condition?

If your child has hemimegalencephaly, they need support from a large medical team. Work with your child's doctors to create a care plan that fits your child's specific needs. Your care team may include:

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

Questions to Ask Your Child's Doctor

If your child is diagnosed with hemimegalencephaly, ask your doctor these questions:

• What type of hemimegalencephaly does my child have?
• Does my child have any other medical conditions?
• What is the best treatment plan for my child?
• What is my child's long-term outlook?
• What can we do at home to reduce their symptoms?

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