What do the hemispheres of the brain do?
The largest part of the brain, the cerebrum, is organized into two hemispheres. In most people, the two hemispheres perform distinct functions.
- The left hemisphere is dominant for language in most people and plays an important role in verbal memory, reading, writing and arithmetic. It is concerned with sensation and movement on the right side of the body.
- The right hemisphere plays a large part in interpreting what we see and touch, and in non-verbal memory, music, and emotions. It is concerned with sensation and movement on the left side of the body.
The left hemisphere dominates language in almost all right-handed people and in many left-handed people. In some people, though, the two hemispheres share the language function more equally, and in a few people the right hemisphere may be dominant for language function. Right hemisphere and bilateral (two-sided) language centres are more common in young children and children with epilepsy.
What is a hemispherectomy?
The term "hemispherectomy" used to refer to the removal of one hemisphere, or one side, of the brain. Complete removal of one hemisphere (called anatomical hemispherectomy) has more complications, so most neurosurgeons perform a functional hemispherectomy, in which only some sections of the brain are removed and other sections are disconnected. The end result of a functional hemispherectomy is that half the brain is completely disconnected from the other half and totally inactive. Your child's neurologist and neurosurgeon will discuss the best surgical procedure for your child. However, when a functional hemispherectomy does not stop seizures, an anatomic hemispherectomy may be considered to help control seizures.
The aim of a hemispherectomy is to remove or disconnect that hemisphere that is least used and the source of your child’s seizures. During this procedure, the corpus callosum (the bridge which connects the two hemispheres of the brain) is also cut (callosotomy) to prevent the spread of seizures from the dysfunctional hemisphere to the functional hemisphere.
Newborns and very young infants who are hemispherectomy candidates may be too small to undergo this surgery, as they are at high risk of blood loss. Recently, a new less invasive procedure, called endovascular embolization has been used in these babies to achieve seizure freedom.
Endovascular embolization involves using catheters introduced inside blood vessels to selectively block blood flow to the abnormal areas of the brain, effectively “disconnecting” the problematic hemisphere while preserving healthy tissue. The technique essentially targets dysfunctional areas of the brain, and by cutting the connection, protects the functioning half of the brain.
When is a hemispherectomy considered?
Hemispherectomy is considered when:
- seizures have persisted, despite trying medication (monotherapy and polytherapy) for at least two years
- pre-surgical evaluation shows epileptic activity arising from one hemisphere
- the child has weakness on one side of the body
Hemispherectomy is often used for intractable seizures (seizures that cannot be controlled with medication) associated with hemimegaloencephaly (overgrowth of one side of the brain). Hemispherectomy is also used in children with a dysfunctional hemisphere as a result of Rasmussen's encephalitis or Sturge-Weber syndrome. Some other indications include malformations of cortical development and epilepsy as a result of perinatal stroke.
Generally, the earlier in life that this operation is done the more likely the child is to compensate for the loss of one hemisphere. The younger the child, the more flexible (plastic) the brain is and the better the remaining side can compensate for the operated side. However, the child must be at least several months old before they can have the surgery.
Before surgery
A thorough pre-surgical evaluation is essential to confirm that there is no other treatment option. This may include:
- EEG and MRI to help identify the dysfunctional hemisphere
- functional mapping using fMRI, a Wada test or MEG to determine which hemisphere is dominant for critical functions such as speech and memory (if the child is old enough)
- neuropsychological tests to establish your child's baseline functioning
The surgeon and the team will explain the surgery to you and discuss all related issues. They will instruct you on any specific steps to take before the operation.
They will also discuss post-operative symptoms, any intensive care and rehabilitation that will be required and possible ongoing deficits and care.
Surgery
The operation will take about six hours and will require a general anesthetic.
Your child will be put to sleep under general anesthesia. A portion of their head will be shaved. Part of the scalp and bone will be removed and the dura membrane will be peeled back to expose the region of the brain to be removed.
During the operation, the surgeon may remove some parts of the brain and disconnect other parts. The corpus callosum is also cut to prevent the spread of any seizures to the functional side of the brain.
After the operation, the bone will be replaced and the scalp will be sutured closed. Your child will spend a few hours in the recovery room until they wake up and one or two days in the intensive care unit, followed by about a week at the hospital.
Possible side effects after surgery
Intensive care will be necessary at first.
Your child may experience scalp numbness, nausea, fatigue, depression, headaches and difficulty with speech and memory. Some of these symptoms may be temporary and others may continue.
Neuropsychological testing will be done to determine any changes in your child's ability. Ongoing monitoring will also be necessary to determine any long-term effects.
Hemispherectomy causes loss of movement and/or sensation on the side of the body opposite the hemisphere that was removed. Your child will need rehabilitation to help them with weakness, movement problems, difficulty in walking and speech problems. In the hospital, physical, occupational and speech therapists will work with your child to assess their needs and help them adjust. Other types of rehabilitation may also be necessary.
Once your child is at home, they may need to continue using the services of a physical or occupational therapist in the community. The treatment team will discuss this with you and may be able to help you find a therapist.
What can I expect from the surgery?
Every child is different. Depending on the nature of your child's seizures and the location of the epileptogenic region, surgery may result in complete seizure control or "partial" seizure control with less need for medication. Between 66% of children to more than 80% of children who undergo hemispherectomy are completely seizure-free. Most of the rest of the children who have hemispherectomy have fewer seizures after the operation. If your child has persistent seizures after an initial procedure, their health-care provider will do a careful evaluation to see if they could benefit from repeat surgery.
There may also be some chance that the surgery will not improve seizures. Talk to your child's health-care provider about what you and your child can realistically expect as a result of the surgery.
Complications and risks
Every surgical procedure has related risks including infection, bleeding, cerebral edema (swelling) and allergy to or complications from anesthetic. Other risks of hemispherectomy include developmental problems and loss of peripheral vision. Children who undergo anatomical hemispherectomy are at higher risk of these complications and are also at risk of hydrocephalus.
Your child's health-care provider will discuss the risks of this procedure with you in detail.
Ongoing care
After discharge from the hospital, children often need rehabilitation services. Your child may be transferred to a rehabilitation facility for intensive physical, occupational and speech therapy. After that, rehabilitation therapy may be continued at home and school.