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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.
A functional hemispherectomy is a procedure in which portions of one
hemisphere-which is not functioning normally (called the non-functioning
hemisphere)-are removed, and the corpus callosum is split. This disconnects the
communications between the various lobes of the epileptic hemisphere and between
the two hemispheres, preventing the spread of seizures to the functional side of
the brain.
Who is a candidate for a functional hemispherectomy?
This procedure generally is used only for people who do not experience
improvement in their condition after taking medication(s) and who have severe,
uncontrollable seizures beginning in a non-functioning hemisphere. This type of
epilepsy often occurs in young children who have an underlying disease, such as
Rasmussen's encephalitis or Sturge-Weber syndrome, which has damaged the
hemisphere. (Rasmussen's encephalitis and Sturge-Weber syndrome are progressive
disorders that affect only one side of the brain.)
What happens before surgery?
Candidates for functional hemispherectomy undergo an extensive pre-surgery
evaluation-including seizure monitoring with video recordings,
electroencephalography (EEG) and magnetic resonance imaging (MRI). These tests
help the doctor identify the damaged hemisphere and confirm it as the source of
the seizures.
An intracarotid amobarbital test also called a WADA test, or functional MRI,
may be 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 understanding speech.
What happens during surgery?
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 surgery?
The patient generally stays in an intensive care unit for 24 to 48 hours and
-then stays in a regular hospital room for 3 to 4 days. Most people who have a
functional hemispherectomy will be able to return to their normal activities,
including work or school in 6 to 8 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 percent of people who have a functional hemispherectomy will
experience significant improvement, and about 60 percent 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 surgery?
The following symptoms may occur after surgery, although they generally go
away on their own:
- Scalp numbness
- Nausea
- Muscle weakness on the affected side of the body
- Puffy eyes
- Feeling tired or depressed
- Difficulty speaking, remembering things 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 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
- Damage to the functional hemisphere
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