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 language, 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.
The term "hemispherectomy" used to refer to the removal of one hemisphere, or one side, of the brain. Complete removal of one hemisphere has some associated complications, so some neurosurgeons prefer to 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.
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 is also cut (callosotomy) to prevent the spread of seizures from the dysfunctional hemisphere to the functional hemisphere.
Indications
Hemispherectomy is considered when:
- seizures have persisted, despite trying medication (monotherapy and polytherapy) for at least two years
- pre-surgical evaluation shows multifocal epileptic activity (seizures arising from several areas of the brain) restricted to one hemisphere.
Hemispherectomy is often used for intractable seizures associated with hemimegalencephaly (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.
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 prior to 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 anaesthetic.
Your child will be put to sleep under general anaesthesia. 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 come out of anaesthesia 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. There may also be some chance that the surgery will not improve things. Talk to your child's doctor 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 anaesthetic. Other risks of hemispherectomy include developmental problems and loss of peripheral vision.
Your child's doctor will discuss the risks of this procedure with you in detail.
