The corpus callosum, a structure in the brain made up of white-matter fiber tracts, is the most important connection between the two halves of the brain. Its normal function is to mediate communication between the two hemispheres of the brain. Seizures may spread rapidly from one hemisphere to the other by way of the corpus callosum.
Severing a part or all of the corpus callosum greatly reduces this spread. It also stops or decreases the frequency of “drop attacks” from certain types of generalized seizures (atonic seizures).
This procedure has no impact on partial seizures, which arise focally from a specific part of the brain.
Corpus callosotomy (callosal sectioning) is quite effective in reducing seizure frequency in patients who have generalized epilepsy with drop attacks. It is generally reserved for this selected population. It is not a curative epilepsy surgery procedure, but is rather considered palliative.
Callosal sectioning is often done in stages. The anterior two-thirds of the corpus callosum is sectioned first. Then, if necessary, the posterior one-third is sectioned in a second surgical procedure.
Generally, a frontal craniotomy is performed adjacent to the midline. One hemisphere (the nondominant one, usually the right) is gently retracted to expose the corpus callosum, which lies at the depth between the two hemispheres. Microsurgical technique is used to section the corpus callosum in the midline. Great care is exercised to prevent injury to the adjacent anterior cerebral arteries during this procedure.
One risk of the procedure is that the patient tends to neglect the nondominant extremities initially, but recovery usually occurs within a few weeks. Neglect of the nondominant extremities is likely to be more profound after complete corpus callosotomy. Other interhemispheric white-matter pathways become more functional with time.
Complete callosal sectioning can cause some permanent deficits. When the patient’s eyes are closed, one side of the brain does not cooperate with the other in even simple tasks, so the right and left extremities may carry out conflicting movements. With eyes open, the patient can compensate for this problem. These complications are called disconnection syndromes.
More serious complications are exceedingly rare. In the early days of callosal sectioning, before the development of modern neurosurgical techniques and advances in microsurgery, problems were more frequent.
Reviewed and revised January 2004 by Howard Weiner, MD, New York University.
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