Epilepsy and Functional Hemispherectomy

What Is a Functional Hemispherectomy?

The largest part of the brain, the cerebrum, can be divided down the middle lengthwise into two halves, called hemispheres. A deep groove splits the left and right hemispheres, which communicate through a thick band of nerve fibers called the corpus callosum. Each hemisphere is further divided into four paired sections, called lobes -- the frontal, parietal, occipital, and temporal lobes.

The two different sides or hemispheres are responsible for different types of activities. The left side of the brain controls the right side of the body and vice versa. For most people, the ability to speak and understand the spoken word is a function of the left side of the brain. A functional hemispherectomy is a procedure in which portions of one hemisphere -- which are causing the seizures -- are removed, and the corpus callosum, which connects the two sides of the brain, is cut. This disconnects communication between the two hemispheres, preventing the spread of electrical seizures from one side of the brain to the other. As a result, the person usually has a marked reduction in physical seizures.

Who Is a Candidate for a Functional Hemispherectomy?

This procedure generally is used only for people with epilepsy who do not experience improvement in their condition after taking many different medications and who have severe, uncontrollable seizures. This type of epilepsy is more likely to be seen in young children who have an underlying disease, such as Rasmussen's encephalitis or Sturge-Weber syndrome, that has damaged the hemisphere.

What Happens Before a Functional Hemispherectomy?

Candidates for functional hemispherectomy undergo an extensive pre-surgery evaluation -- including seizure monitoring, electroencephalography (EEG), and magnetic resonance imaging (MRI). These tests help the doctor identify the damaged parts of the brain and confirm that it is the source of the seizures. An intracarotid amobarbital test, also called a WADA test, is done to determine which hemisphere is dominant for critical functions such as speech and memory. During this test, each hemisphere is alternately injected with a medication to put it to sleep. While one side is asleep, the awake side is tested for memory, speech, and ability to understand speech.


What Happens During a Functional Hemispherectomy?

A functional hemispherectomy requires exposing the brain using a procedure called a craniotomy. "Crani" refers to the skull and "otomy" means "to cut into." After the patient is put to sleep (general anesthesia), the surgeon makes an incision (cut) in the scalp, removes a piece of bone and pulls back a section of the dura, the tough membrane that covers the brain. This creates a "window" in which the surgeon inserts special instruments for removing brain tissue. Surgical microscopes are utilized to give the surgeon a magnified view of the brain structures. During the procedure, the surgeon removes portions of the affected hemisphere, often taking all of the temporal lobe but leaving the frontal and parietal lobes. The surgeon also gently separates the hemispheres to access and cut the corpus callosum. After the tissue is removed, the dura and bone are fixed back into place, and the scalp is closed using stitches or staples.

What Happens After a Functional Hemispherectomy?

The patient generally stays in an intensive care unit for 24 to 48 hours and then stays in a regular hospital room for three to four days. Most people who have a functional hemispherectomy will be able to return to their normal activities, including work or school in six to eight weeks after surgery. Most patients will need to continue taking anti-seizure medication, although some may eventually be able to stop taking medication or have their dosages reduced.

How Effective Is Functional Hemispherectomy?

About 85% of people who have a functional hemispherectomy will experience significant improvement in their seizures, and about 60% will become seizure-free. In many cases, especially in children, the remaining side of the brain takes over the tasks that were controlled by the section that was removed. This often improves a child's functioning and quality of life, as well as reduces or eliminates the seizures.

What Are the Side Effects of a Functional Hemispherectomy?

The following symptoms may occur after a functional hemispherectomy, although they generally go away over time and with therapy:

  • Scalp numbness.
  • Nausea.
  • Muscle weakness on the affected side of the body.
  • Puffy eyes.
  • Feeling tired or depressed.
  • Difficulty speaking, remembering, or finding words.
  • Headaches.


What Risks Are Associated With a Functional Hemispherectomy?

The risks associated with a functional hemispherectomy include:

  • Risks associated with surgery, including infection, bleeding, and an allergic reaction to anesthesia.
  • Loss of movement or sensation on the opposite side of the body.
  • Swelling in the brain.
  • Delayed development.
  • Loss of peripheral (side) vision.
  • Failure to control seizures.

WebMD Medical Reference Reviewed by Neil Lava, MD on May 07, 2016



National Institute of Neurological Disorders and Stroke: "Seizures and Epilepsy: Hope Through Research."

Epilepsy Foundation: "Procedures."

Epilepsy Foundation: "Types of Surgery."


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