Is one side of your baby's brain too big? Let's learn about hemimegalencephaly!

Have you ever been concerned about the shape of your little one's head, or about the frequent fits he or she has? Sometimes, there may be a very rare medical condition behind these things. Hemimegalencephaly is one such condition. Although the name may sound a bit complicated, let's talk about it simply.

What is Hemimegalencephaly?

Simply put, hemimegalencephaly is when one side of your child's brain (cerebral hemisphere) is abnormally larger than the other. Think of our brain as a large tumor with two halves, a left and a right side. In this condition, only one side grows larger than it should. Sometimes this enlargement can be limited to a small part of that side of the brain , or the entire side can become enlarged.

When one side of the brain gets bigger in this way, other changes can occur within the brain. For example:

• Neurons are a type of cell in our brain. They may not be properly organized (cytoarchitecture) or the top layer of the brain may not be properly formed (cortical dysplasia).
• Missing or damaged corpus callosum: This is like a bridge connecting the two sides of the brain . If it is missing or damaged, problems can occur.
• Enlargement of the fluid-filled cavities (ventricles) of the brain on the affected side.

Because parts of the brain are not properly developed in this way, seizures can occur frequently. We also call this epilepsy . Often, these seizures are difficult to control with ordinary antiseizure medications . If the seizures cannot be controlled with medication, many children have to undergo brain surgery (epilepsy surgery).

Are there main types of hemimegalencephaly?

Yes, there are several main types of this condition:

• Isolated hemimegalencephaly: This affects only the outermost layer of the child's brain (cerebral cortex). There is no involvement of the skin or other organs.
• Syndromic hemimegalencephaly: This affects not only the brain, but also the baby's skin and some other organs. However, skin symptoms may appear months or even years after birth. Also, one side of the baby's body may be larger than the other (hemihypertrophy).
• Total hemimegalencephaly: In this, the child's cerebellum and sometimes even the brainstem become enlarged. This can occur either isolated or syndromic.

What are the symptoms of this condition?

The first symptom you may notice is your baby having ``infantile spasms or seizures ''. These are usually focal seizures. This means that only one side of the baby's body may twitch.

Other symptoms that may be seen include:

• Enlarged head (Macrocephaly).
• Uneven head shape.
• Difficulty with movements such as walking and running.
• Numbness and weakness on one side of the body.
• Developmental delays: This means being late in talking, playing, and learning in a way that is appropriate for their age.
• Visual impairments: For example, half of the visible range is lost when looking with both eyes (hemianopia).

What causes hemimegalencephaly?

In fact, scientists still don't know exactly what causes this condition. Some believe it's genetic, meaning it's caused by a change in the child's DNA . But it's not hereditary. That means you have the condition and it's not something you pass on to your child.

Most likely, around the third week of pregnancy, a random, or spontaneous, change in one of the genes important for brain development occurs. Remember, this condition is not caused by anything you did during pregnancy. This is not your fault or the father's fault.

What are the risk factors that affect this condition?

Hemimegalencephaly can occur in conjunction with other genetic conditions. This means that children with the following conditions are at increased risk of developing hemimegalencephaly:

• `Epidermal nevus syndrome`
• `Klippel-Trenaunay syndrome`
• `McCune-Albright syndrome`
• ``Neurofibromatosis Type 1 (NF1)''
• `CLOVES syndrome`
• `Proteus syndrome`
• `Hypomelanosis of Ito`

How is hemimegalencephaly diagnosed?

To find out for sure if this is the case, your child's doctor will first examine your child and ask you about your child's health history. Then, they may do the following tests:

• A brain MRI scan.
• EEG (Electroencephalogram) test. This measures the electrical activity of the brain.

With today's advanced technology, it is sometimes possible to diagnose this condition while the baby is still in the womb ``during pregnancy.`` This is done by performing a special MRI scan of the baby's brain ``fetal MRI``.

How is it treated?

The main goal of treating hemimegalencephaly is to control the seizures. These seizures can sometimes begin at a very young age and are often difficult to control with medication (drug-resistant).

This condition can cause a variety of fits. It is important to note that a fit that occurs in childhood, especially if it begins in infancy, can have a significant impact on a child's development. Uncontrolled fits can seriously damage a child's growth and development, as well as damage the developing brain. Therefore, it is important to stop the fit as soon as possible.

Treatment for seizures begins with anti-seizure medication. Some children can control their seizures for the rest of their lives with these medications. But many develop drug-resistant epilepsy. Then a surgery called a hemispherectomy is performed. This involves removing the affected part of the child's brain (cerebral cortex) or separating it from the other side of the brain.

When this surgery is performed, it is sometimes called a "functional hemispherectomy." In this surgery, the surgeon cuts and separates the tissue and nerves that connect one side of the child's brain to the other, but the abnormally enlarged side of the brain can be left inside the skull. In an "anatomical or complete hemispherectomy," one side of the brain is separated from the other side, removing the abnormal side entirely. This surgery should be performed by a neurosurgeon who has special training in epilepsy surgery.

Is the operation to remove half of the brain (hemispherectomy) difficult?

In fact, hemispherectomy is a very difficult brain surgery. There are several reasons why performing this surgery is even more difficult due to the condition hemimegalencephaly.

The first thing is that blood vessels are often located in an unusual way. Therefore, they are difficult to find and cut during surgery. This can sometimes cause excessive bleeding.

In addition, because the entire brain of a child is abnormally shaped, the landmarks that a surgeon uses to identify individual parts of the brain are often not visible. Also, infants and young children can lose a significant amount of blood during this surgery. This must be monitored very carefully and blood must be replaced as needed.

Therefore, it is very important that the medical team treating your child is a skilled and experienced team in this surgery. It is safer for your child to have this surgery performed in a hospital that routinely performs hemispherectomy for babies with hemimegalencephaly and has extensive experience in this procedure.

What is the prognosis for a child with this condition?

How your child's condition will develop depends largely on how well the fit can be controlled and whether the abnormal brain development is on one side or both sides.

Hemimegalencephaly is a spectrum condition that affects each child differently. This means that the results can vary greatly from child to child.

• Many children may have some level of intellectual disability .
• Some children who have well-controlled fits may have near-normal intelligence.
• But for some other children, things like walking, talking, and intellectual development can be seriously affected.

Almost all children with hemimegalencephaly develop weakness on one side of the body (hemiparesis) . This is a type of cerebral palsy. Some children may have mild weakness, while others may have severe weakness. Some children may have a condition called homonymous hemianopsia, where half of their visual field is lost. Many children can walk and talk, but not all children can. Some children need special feeding aids, while others can eat normally.

A recent study found that after surgery:

• The fit has completely stopped in 68% of children.
• 43% of the children had average or mildly impaired intelligence.
• 26% of children have been able to speak in an age-appropriate manner.
• 21% of children have been able to read at a sufficient level.

Can hemimegalencephaly be prevented?

Since scientists still don't know exactly what causes this condition, there is no way to prevent it.

How do you take care of a child with this condition?

If your child has hemimegalencephaly, they will need the support of a large medical team. Together with your child's medical team, you can develop a plan that meets your child's needs. Your child's medical team may include:

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

What questions should you ask your child's doctor?

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

• What type of hemimegalencephaly does my child have?
• Does my child have any other medical conditions?
• What is the best treatment?
• What is my child's outlook?
• What can we do to reduce his symptoms?

Mom and Dad, a little bit of courage! (Take-Home Message)

We know that seeing your child have a seizure, or learning that they have a condition like Hemimegalencephaly, can be a huge shock and a heartbreaking experience. But remember, you are not alone. The medical team treating your child is with you every step of the way.

If you are struggling to cope with this situation, ask your doctor about support groups that help families of children with hemimegalencephaly. Talking to parents of children with this condition can help you to reduce your fears and come to terms with your child's condition. They can be a great source of strength for you as your child learns to live with the condition.

` Hemimegalencephaly, abnormal brain development, infantile epilepsy, brain surgery, developmental delays, genetic conditions, neurological diseases