Definition & Overview

Cerebrum, which is the largest part of the human brain, is composed of the left and the right hemispheres. Each is responsible for distinct physiological, emotional, and mental functions.

Hemispherectomy is a surgical procedure for removing half of the brain or, in some cases, rendering the affected part inactive by disconnecting it from the rest of the brain. This partial brain removal technique is developed to prevent the spread of epileptic seizures from the originating affected part.

There are two types of hemispherectomy, namely anatomic and functional. While the former refers to the removal of one hemisphere, the latter renders the affected part nonfunctional. Between the two, the former is preferred since the connecting fibres within the brain and the corpus callosum are only severed but left intact, which means minimal trauma and complications.

Who Should Undergo & Expected Results

Partial brain removal is one of the options considered for the treatment of epilepsy if the condition does not respond to medication. This procedure, which eliminates or reduces seizure episodes, is typically recommended for infants or young children who show much higher adaptability to the loss of brain matter.

Also, patients who suffer seizures for more than two years and whose condition show no noticeable improvement after monotherapy and polytherapy are good candidates for hemispherectomy. However, physicians need to make sure that the epileptic activity is confined to only one hemisphere for this procedure to be recommended and performed.

Children who develop abnormal overgrowth on one side of the brain, termed hemimegaloencephaly, are also potential candidates for partial brain removal. Rasmussen's encephalitis or Sturge-Weber syndrome could also cause abnormal functioning of one hemisphere and might be treated with hemispherectomy.

General positive outcomes are expected, especially in young children who undergo the procedure before their first birthdays. This is because the remaining hemisphere would have greater capacity to compensate for the loss of its counterpart. The younger the patient, the better are the chances of regaining cognitive functions. These could result in the child having a far better quality of life and no longer depending on anticonvulsant medications. Hospitalisation is required for several weeks and patients are required to undergo rehabilitation to assist the body in the recovery of mental and physiological functions. For older patients, there might be marked changes in their personalities and decision-making capabilities, depending on which area of the brain was removed or disconnected.

Those with developmental and vascular problems before surgery might experience exacerbation of their conditions after partial brain removal.

How Does the Procedure Work?

The patient is sedated and a part of the head is shaved in preparation for the incision. A craniotomy is then performed in which a small opening is drilled through the skull to expose and open the dura mater, the brain's protective cover.

The affected area is then determined and located through brain mapping. This process uses specialised tools like subdural electrodes and electrical probes. In some cases, patients are purposely kept awake to interact with the surgeon and determine which areas are associated with sensation, vision, or communication. The surgeon then carefully removes or disconnects the area where seizures originate. Afterwards, the dura mater is stitched up and closed, and the bone flap is reattached using titanium plates and screws. The incisions on the head are also sutured back.

Possible Complications and Risks

During surgery, there is always the risk of adverse reaction to anaesthesia, bleeding, and blood clotting. If craniotomy was performed, there is also a possible occurrence of stroke or seizures. The patient could also experience electrolyte imbalance, hypothermia, or aseptic meningitis as well as brain swelling, leaking of the cerebrospinal fluid, or damage to the nearby nerves that translates to the loss of physical and mental functions. Rare cases report permanent brain damage.

Post-operatively, patients may experience memory and language problems as the brain is still in the recovery phase. Some also report reduced or double vision. In some cases, the patient would continue to experience seizures, though less severe compared to those before the partial brain removal. An intense rehabilitation program would be required to recover near normal functions. Some complications, like hydrocephalus or recurrent seizures, can manifest even after several years following surgery and would need immediate attention.


  • National Institute of Neurological Disorders and Stroke: "Seizures and Epilepsy: Hope Through Research."
Share This Information: