What to Expect From a Hemispherectomy

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Epilepsy surgery is an option that is becoming more frequently used as techniques become better refined and as outcomes improve.

Hemispherectomy is among the oldest surgical techniques for epilepsy. It is a procedure that involves removing part of the brain and disconnecting areas of the brain to reduce seizures. Over the past years, the procedure has evolved, with improved safety and results.


Most of the time, a hemispherectomy is used for children with certain types of epilepsy, but some adults can also benefit from the procedure.

Hemispherectomy may be considered a possibility for you if you have intractable epilepsy, which means that seizures are frequent, severe, and cannot be controlled with tolerable medication doses.

It is also an option for certain types of epilepsy known to respond well to hemispherectomy. The most common ones include:

  • Rasmussen's encephalitis: This is a rare syndrome that often results in persistent, difficult to control seizures. Rasmussen's encephalitis may necessitate treatment with surgical procedures such as hemispherectomy or corpus callosotomy.
  • Cortical malformation: For unexplained reasons, children may be born with subtle malformations of the brain that can cause seizures.
  • Perinatal stroke: Perinatal stroke occurs before a baby is born or shortly afterward. This may cause problems with brain function, such as seizures.


    There are a number of types of hemispherectomy, and your medical team will determine the best plan based on your epilepsy pattern and your pre-surgical testing. The different hemispherectomy procedures all have several features in common, including removal of brain tissue and surgically dividing areas of the brain.

    The purpose of removing a region of the brain is to eliminate an area or areas that have been shown to cause seizures on your EEG. The purpose of severing communication between areas of the brain is to prevent erratic electrical activity in the brain from spreading and causing seizures.

    The most common types of hemispherectomy are:

    • Anatomic: This procedure is the most extensive type of hemipherectomy and involves removing portions of the left or right hemisphere to reduce seizure activity. While this seems rather extreme, people who undergo anatomic hemispherectomy are able to survive, and even function quite well. There may be some loss of abilities, however, particularly in skills related to left-right distinction and spatial perception (the ability to appreciate three dimensions and to recognize one’s own body parts).
    • Traditional functional: This type of hemispherectomy involves removal of a small section of brain tissue from the hemisphere responsible for causing seizures, as well as separation of the corpus callosum.
    • Peri insular: This procedure is more limited in terms of removing brain tissue than some of the more traditional procedures. It does involve removal of limited amounts of brain tissue and surgically severing connections between areas of the brain, as well as cutting all or part of the corpus callosum.

      As you may expect, the more extensive procedures have a higher association with complications.


      Prior to having surgery, you will need pre-surgical testing. These tests determine whether epilepsy surgery is expected to help you, which type of surgery is best for you, and also help guide your doctors in planning the procedure itself. The locations of the regions to be removed are selected to avoid causing loss of brain function. Some tests that you may need prior to hemispherectomy include: 

      • EEG: An EEG is an electroencephalogram, which is a non-invasive test that measures the electrical activity of the brain by superficially placing flat electrodes on the scalp. This test can help determine which region of the brain is responsible for seizures. In the context of planning a hemispherectomy, an EEG can identify which area should be removed or severed for maximum seizure control.
      • Video EEG: This is an EGG test that is accompanied by video monitoring. Video EEG allows your medical team to observe how the EEG seizure activity manifests and when your most problematic seizures begin in relation to your EEG changes. Pinpointing this association can help in planning your procedure, particularly if you have several types of seizures and several areas of abnormal activity noted on EEG.
      • Brain MRI: A brain MRI is a detailed picture of the brain. It can identify congenital (from birth) abnormalities as well as acquired abnormalities that may be causing your seizures.
      • PET scan: This is an imaging test that evaluates the metabolism (energy consuming activity) in different parts of the brain. It may be useful in determining the anatomic location of your seizures.
      • WADA test: This test evaluates the location of language function in your brain. A WADA test is not used to identify seizure activity or location but is used to help strategically plan your procedure to minimize loss of function after surgery.


      Your procedure is tailored for you based on your pre-surgical testing, and may not be exactly the same as someone else’s hemispherectomy procedure.

      Hemispherectomy surgery involves creating an opening in part of the skull to obtain access to the brain, and carefully removing the region of the brain that was identified for removal prior to surgery. During surgery, the areas that your doctors planned to disconnect, such as the corpus callosum, are carefully severed. And any bone that was removed during surgery is put back into place in the operating room.

      Ventricular Shunt

      Most people who have hemispherectomy need a ventricular shunt, usually temporarily. This is a tube that collects fluid to prevent excess fluid build up from harming the brain.

      Brain surgery itself may cause a temporary buildup of fluid. Removal of brain tissue also causes a build-up of fluid, which flows into the newly unfilled space. However, over time, the fluid balance is expected to normalize. If there is a potential problem with continuing buildup of fluid, a shunt may be maintained for the long term.


      As you recover from surgery, you will need close monitoring. You will have stitches on your scalp and your bone will slowly heal on its own.

      As you recover, your medical team evaluates your level of alertness and your neurological function to monitor for improvement and also to identify any complications, such as bleeding or swelling. Your shunt will be closely monitored for fluid level, blood, and signs of infection. This can help your medical team catch and prevent problems before they become advanced. 

      You may feel a bit dizzy or off balance and you may need assistance with eating or with some of your activities of daily living, such as going to the bathroom and bathing, for a few days or even a few weeks. You should expect to get stronger, improve your balance and become more independent over the days and weeks after surgery.

      As you recover, be sure to tell your medical team about any unusual feelings that seem to be like a seizure or an aura.


      On follow up, most people who have had a hemispherectomy experience substantial improvement of seizures. Some people experience complete improvement of their epilepsy and are able to stop taking anti-seizure medication after the procedure. Most people who have had a hemispherectomy need to continue taking anti-seizure medication for seizure control, but are able to take more tolerable doses of medication than prior to surgery.

      Sometimes, a repeat hemispherectomy may be needed, and the outcomes reported from repeat hemispherectomy are very good. It is rare for seizures to worsen after a hemispherectomy.

      A Word From Verywell

      A hemispherectomy is a significant surgical procedure. If you have been considering a hemispherectomy for seizure control, you should know that the procedure is performed by experienced surgeons who have been trained in epilepsy surgery and certified in brain surgery. The pros and cons of medication, nerve stimulators, and interventional surgical procedures are weighed carefully to ensure that the safest and most effective options are selected for your specific seizure control.

      If hemispherectomy is selected as the best option for you, your pre-surgical testing can minimize or completely eliminate loss of brain function from the surgery. If you need to take medications or have repeat surgery, the outcomes in terms of seizure control and side effects are favorable, with most people experiencing fewer and less severe seizures after hemispherectomy than they did prior to the surgery.


      Chen S, Guan Y, Liu C, et al. Treatment for patients with recurrent intractable epilepsy after primary hemispherectomy. Epilepsy Res. 2017;139:137-142. doi: 10.1016/j.eplepsyres.2017.11.021 .