A hemispherectomy is a surgical procedure to remove, disable or disconnect one hemisphere of the brain. It is a very rare procedure of last resort to treat severe seizures that are localized in one area of the brain. It is generally only used when a patient's seizures cannot be controlled by medication and are severe and frequent enough to impair a major life function or put the patient's life at risk. It is generally not performed merely because a patient suffers frequent seizures if they otherwise have high mental functioning.
In over 85% of cases, the procedure controls or ends the patient's seizures. In addition, in many cases, it actually improves the patient's cognitive functions. It also appears to have few or no long-term effect on patients.
When the operation was first used for therapeutic purposes in the 1960s, the entire hemisphere was surgically removed. However, in modern practice, only those parts of the brain involved in the seizure are actually removed. This decreases blood loss and the chances of complications. New experimental techniques, which are gaining favor, merely make the hemisphere non-functional by removing its connections to the other hemisphere of the brain and the nervous system rather than surgically removing any part of it. This procedure can be performed with a laproscope, resulting in faster recovery.
The procedure is less likely to be performed on adults as they are less likely to benefit from it. Children appear to have a better chance of recovery and improvement from the procedure. In very rare cases, it can be performed on a person who has suffered a major brain trauma, such as a gunshot wound to the head.