Patients who have congenital hemiplegia and atrophy or poor development of one cerebral hemisphere may also have broad areas of almost continuous seizure discharges over that hemisphere. Often, seizures in these individuals are refractory to medication. In some of these patients, the seizure discharges cross the corpus callosum and interfere with the function of the opposite, normal hemisphere as well. Cognitive function may be severely handicapped, as is normal fine movement of the foot and hand on the side opposite the affected hemisphere.
If the affected cerebral cortex—which is propagating significant seizure discharges but is not mediating useful neurologic function—is removed surgically, these patients will often experience dramatic improvement not only in seizure control, but also in overall neurologic function. This improvement is the result of eliminating the negative effect of the impaired hemisphere on the unaffected, normal side of the brain. This surgical procedure is called hemispherectomy.
Patients are considered for hemispherectomy if they have one of a variety of neurologic disorders that typically affect one half of the brain, including:
About 85% to 90% of patients undergoing hemispherectomy experience arrest of their seizures, accompanied in most cases by dramatic improvement in function, including further cognitive development.
Formerly, the entire cortical mantle was removed (“anatomic hemispherectomy”). However, this technique was associated with a late complication characterized by hemorrhage into the large resection cavity, which became filled with cerebrospinal fluid. Sensorineural hearing loss occurred as rising iron levels in the spinal fluid from the breakdown of blood gradually proved toxic to the eighth cranial nerve. Another complication was the occurrence of hydrocephalus.
Current techniques entail disconnecting the white matter fiber connections from the entire cortex to the opposite hemisphere and to the deeper brain structures, while leaving intact the brain substance and vascular structures supporting these cortical areas (“functional hemispherectomy”). This method has a similar success rate for most conditions, except for hemimegalencephaly. Because the empty postoperative cavity in the affected half of the cranium is minimized, the complications associated with anatomic hemispherectomy are greatly reduced.
Overall, the risks are similar to those associated with temporal lobe or frontal lobe resection. There is a slightly higher incidence of hydrocephalus, or accumulation of cerebrospinal fluid within the ventricles of the brain. This condition may require insertion of a shunt, which diverts the fluid to another compartment of the body, where it is absorbed naturally.
Reviewed and revised January 2004 by Howard Weiner, MD, New York University.
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