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The operation known as hemispherectomy—where half the
brain is removed—sounds too radical to ever consider, much less perform.
In the last century, however, surgeons have performed it hundreds of
times for disorders uncontrollable in any other way. Unbelievably, the
surgery has no apparent effect on personality or memory.
The first known hemispherectomy was performed on a dog in 1888 by German
physiologist Friedrich Goltz. In humans, neurosurgeon Walter Dandy
pioneered the operation at Johns Hopkins University in 1923 on a brain
tumor patient. (That man lived for more than three years before
ultimately succumbing to cancer.) The procedure is among the most
drastic kinds of brain surgery—"You can't take more than half. If you
take the whole thing, you've got a problem," Johns Hopkins neurologist
John Freeman quips.
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One side effect Canadian neurosurgeon Kenneth McKenzie reported in 1938
after a hemispherectomy on a 16-year-old girl who suffered a stroke was
that her seizures stopped. Nowadays, the surgery is performed on
patients who suffer dozens of seizures every day that resist all
medication, and which are due to conditions that mostly afflict one
hemisphere. "These disorders are often progressive and damage the rest
of the brain if not treated," University of California, Los Angeles,
neurosurgeon Gary Mathern says. Freeman concurs: "Hemispherectomy is
something that one only does when the alternatives are worse."
Anatomical hemispherectomies involve the removal of the entire
hemisphere, whereas functional hemispherectomies only take out parts of
a hemisphere, as well as severing the corpus callosum, the fiber bundle
that connects the two halves of the brain. The evacuated cavity is left
empty, filling with cerebrospinal fluid in a day or so.
The strength of anatomical hemispherectomies, a specialty of Hopkins,
lies in the fact that "leaving even a little bit of brain behind can
lead seizures to return," Freeman says. On the other hand, functional
hemispherectomies, which U.C.L.A. surgeons usually perform, lead to less
blood loss. "Our patients are usually under two years of age, so they
have less blood to lose," Mathern says. Most Hopkins hemispherectomy
patients are five to 10 years old.
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Neurosurgeons have performed the operation on children as young as three
months old. Astonishingly, memory and personality develop normally. A
recent study found that 86 percent of the 111 children who underwent
hemispherectomy at Hopkins between 1975 and 2001 are either seizure-free
or have nondisabling seizures that do not require medication. The
patients who still suffer seizures usually have congenital defects or
developmental abnormalities, where brain damage is often not confined to
just one hemisphere, Freeman explains.
Another study found that children that underwent hemispherectomies often
improved academically once their seizures stopped. "One was champion
bowler of her class, one was chess champion of his state, and others are
in college doing very nicely," Freeman says.
Of course, the operation has its downside: "You can walk, run—some dance
or skip—but you lose use of the hand opposite of the hemisphere that was
removed. You have little function in that arm and vision on that side is
lost," Freeman says.
Remarkably, few other impacts are seen. If the left side of the brain is
taken out, "most people have problems with their speech, but it used to
be thought that if you took that side out after age two, you'd never
talk again, and we've proven that untrue," Freeman says. "The younger a
person is when they undergo hemispherectomy, the less disability you
have in talking. Where on the right side of the brain speech is
transferred to and what it displaces is something nobody has really
worked out."
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Mathern and his colleagues have recently conducted the first functional
magnetic resonance imaging study into hemispherectomy patients,
investigating how their brain changes with physical rehabilitation.
Probing how the remaining cerebral hemispheres of these patients acquire
language, sensory, motor and other functions "could shed a great deal of
light on the brain's plasticity, or ability to change," Freeman notes.
Still, having half a brain—and therefore only the use of one hand and
half a field of vision in each eye—is a condition most would prefer to
avoid. |