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Hemispherectomy is a very rare surgical procedure where one cerebral hemisphere (half of the brain) is removed or disabled. This procedure is used to treat a variety of seizure disorders where the source of the epilepsy is localized to a broad area of a single hemisphere of the brain, among other disorders. It is solely reserved for extreme cases in which the seizures have not responded to medications or other less invasive surgeries. Common reported complications of a hemispherectomy include: hydrocephalus, subdural fluid collections, CSF leakage, deep and superficial infections. Hemispherectomy is considered the most invasive surgical operation in use today, although not the most dangerous.
Hemispherectomy was first tried on a dog in 1888 by Friedrich Goltz. The first such operation on humans was done by Walter Dandy in 1923 for glioblastoma multiforme. In the 1960s and early 1970s, hemispherectomy involved removing half of the brain, but this resulted in unacceptable complications and side effects in many cases, predominantly filling of excessive body fluids in the skull with subsequent pressure to the remaining brain (known as hydrocephalus). The procedure was revitalized in children in the 1980s by Dr. Ben Carson at Johns Hopkins Hospital. In many centers, this procedure has largely been replaced by the functional hemispherectomy, in which the temporal lobe is removed, a procedure known as corpus callosotomy is performed, and the frontal and occipital lobes are disconnected from the rest of the brain. However the traditional "anatomic" hemispherectomy has remained a viable procedure, due to its superiority in preventing future seizures compared with functional hemispherectomy.
This procedure is almost exclusively performed in children because their brains generally display more neuroplasticity, allowing neurons from the remaining hemisphere to take over the tasks from the lost hemisphere. This likely occurs by strengthening neural connections which already exist on the unaffected side but which would have otherwise remained small in a normally functioning, uninjured brain. In one study of children under 5 who had this surgery to treat catastrophic epilepsy, 73.7% were freed of all seizures.  Studies have found no significant long-term effects on memory, personality, or humor, and minimal changes in cognitive function overall. For example, one case followed a patient who had completed college, attended graduate school and scored above average on intelligence tests after undergoing this procedure at age 5.5. This patient eventually developed "superior language and intellectual abilities" despite the removal of the left hemisphere, which contains the classical language zones. When resecting the left hemisphere, evidence indicates that some advanced language functions (e.g., higher order grammar) cannot be entirely assumed by the right side. The extent of advanced language loss is often dependent on the patient's age at the time of surgery.
Along with neuroplasticity, people who undergo hemispherectomies remarkably recover due to resilience. Resilience is the ability, in this case, of the brain being able to recover from a tough situation and take back its shape. Neuroplasticity resilience explains why the hemisphere that is still intact is able to recover many of the functions that were once the removed hemisphere's job. Resilience here is an action in patients with hemispherectomies in which they recover and navigate back to health.
Although initially thought to be limited solely to children, a study in 2007 indicated the long-term efficacy of anatomic hemispherectomy in carefully selected adults, with seizure control sustainable over multiple decades.
There are cases where a person that received major trauma to one side of the brain, such as a gunshot wound, has required a hemispherectomy and survived. The most notable case is that of Ahad Israfil, who lost the right side of his cerebrum in 1987 in a gun-related work accident. He eventually regained most of his faculties, though he still required a wheelchair. It was noted that reconstructive surgery was difficult due to the gunshot shattering his skull, and he is living with a large indentation on that side of his head.
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