Corpus Callosotomy
Corpus Callosotomy
Definition
Purpose
Demographics
Description
Diagnosis/Preparation
Aftercare
Risks
Normal results
Morbidity and mortality rates
Alternatives
Definition
Corpus callosotomy is a treatment for epilepsy, in which a group of fibers connecting the two sides of the brain, called the corpus callosum, is cut.
Purpose
Corpus callosotomy is used to treat epilepsy that is unresponsive to drug treatments. A person with epilepsy may be considered a good candidate for one type of epilepsy surgery or another if he or she has seizures that are not adequately controlled by drug therapy, and has tried at least two (perhaps more, depending on the treatment center’s guidelines) different anti-epileptic drugs.
The seizures of epilepsy are due to unregulated spreading of electrical activity from one part of the brain to other parts. In many people with epilepsy, this activity begins from a well-defined focal point, which can be identified by electrical testing. Surgical treatment of focal-origin seizures involves removal of the brain region containing the focal point, usually in a procedure called temporal lobectomy. In other people, no focal point is found, or there may be too many to remove individually. These patients are most likely to receive corpus callosotomy.
The purpose of a corpus callosotomy is to prevent spreading of seizure activity from one half of the brain to the other. The brain is divided into two halves, or hemispheres, that are connected by a thick bundle of nerve fibers, the corpus callosum. When these fibers are cut, a seizure that begins in one hemisphere is less likely to spread to the other. This can reduce the frequency of seizures significantly.
The initial surgery may cut the forward two-thirds of the corpus callosum, leaving the rest intact. If this does not provide sufficient seizure control, the remaining portion may be cut.
Demographics
Corpus callosotomy is most often performed for children with “drop attacks,” or atonic seizures, in which a sudden loss of muscle tone causes the child to fall to the floor. It is also performed in people with uncontrolled generalized tonic-clonic, or grand mal, seizures, or with massive jerking movements. Of the 20,000 to 70,000 people in the United States considered candidates for any type of epilepsy surgery, approximately 5,000 receive surgery per year. Between 1985 and 1990, more than 800 corpus callosotomies were performed, and the number has increased since then. Corpus callosotomy is performed by a special neurosurgical team, at a regional epilepsy treatment center.
Description
During corpus callosotomy, the patient is under general anesthesia, lying on the back. The head is fixed in place with blunt pins attached to a rigid
WHO PERFORMS THE PROCEDURE AND WHERE IS IT PERFORMED?
Corpus callosotomy is performed by a neurosurgeon in a hospital operating room.
structure. The head is shaved either before or during the procedure.
Incisions are made in the top of the skull to remove a flap of bone, exposing the brain. The outer covering is cut, and the two hemispheres are pulled slightly apart to expose the corpus callosum. The fibers of the corpus callosum are cut, taking care to avoid nearby arteries and ventricles (fluid-filled cavities in the brain).
Once the cut is made and any bleeding is controlled, the brain covering, bone, and scalp are closed and stitched.
Diagnosis/Preparation
The candidate for any type of epilepsy surgery will have had a wide range of tests prior to surgery. These include electroencephalography (EEG), in which electrodes are placed on the scalp, on the brain surface, or within the brain to record electrical activity. EEG is used to attempt to locate the focal point(s) of the seizure activity.
Several neuroimaging procedures are used to obtain images of the brain. These may reveal structural abnormalities that the neurosurgeon must be aware of. These procedures may include magnetic resonance imaging (MRI), x rays, computed tomography (CT) scans, or positron emission tomography (PET) imaging.
Neuropsychological tests may be done to provide a baseline against which the results of the surgery are measured. A Wada test may also be performed. In this test, a drug is injected into the artery leading to one half of the brain, putting it to sleep, allowing the neurologist to determine where language and other functions in the brain are localized, which may be useful for predicting the result of the surgery.
Aftercare
The patient remains in the hospital for about a week, possibly more depending on any complications that have occurred during surgery and on the health of the patient. There may be some discomfort afterwards. Tylenol with codeine may be prescribed for pain. Bending over should
QUESTIONS TO ASK THE DOCTOR
- Are there any drugs that we haven’t tried that may be effective?
- How long until I can return to school or work?
- Am I a candidate for any other epilepsy surgery?
be avoided if possible, as it may lead to headache in the week or so after the procedure. Ice packs may be useful for pain and itchiness of the sutures on the head. Another several weeks of convalescence at home are required before the patient can resume normal activities. Heavy lifting or straining may continue to cause headaches or nausea, and should be avoided until the doctor approves. A diet rich in fiber can help avoid constipation, which may occur following surgery. Patients remain on anti-seizure medication at least for the short term, and may continue to require medication.
Risks
There is a slight risk of infection or hemorrhage from the surgery, usually less than 1%. Disconnection of the two hemispheres of the brain can cause some neuropsychological impairments such as decreased spontaneity of speech (it may be difficult to bring the right words into one’s mind) and decreased use of the non-dominant hand. These problems usually improve over time. Complete cutting of the corpus callosotomy produces more long-lasting, but very subtle deficits in connecting words with images. These are usually not significant, or even noticed, by the patient.
Normal results
Patients typically experience a marked reduction in number and severity of seizures, with a small percentage of people becoming seizure free. Drop attacks may be eliminated completely in approximately 70% of patients. Other types of seizure are also reduced by 50% or more from corpus callosotomy surgery.
Morbidity and mortality rates
Serious morbidity or mortality occurs in 1% or less of patients. Combined major and minor complication rates are approximately 20%.
Alternatives
Newer anti-seizure medications have partially replaced corpus callosotomy. Focal epilepsy is treated with focal surgery such as temporal lobectomy or hemispherectomy. Vagus nerve stimulation is an alternative for some patients.
Resources
BOOKS
Devinsky, O. A Guide to Understanding and Living with Epilepsy. Philadelphia: EA Davis, 1994.
ORGANIZATIONS
Epilepsy Foundation.www.epilepsyfoundation.org.
Richard Robinson
Corpus Callosotomy
Corpus callosotomy
Definition
Corpus callosotomy is a treatment for epilepsy, in which a group of fibers connecting the two sides of the brain, called the corpus callosum, is cut.
Purpose
Corpus callosotomy is used to treat epilepsy that is unresponsive to drug treatments. A person with epilepsy may be considered a good candidate for one type of epilepsy surgery or another if he or she has seizures that are not adequately controlled by drug therapy, and has tried at least two (perhaps more, depending on the treatment center's guidelines) different anti-epileptic drugs.
The seizures of epilepsy are due to unregulated spreading of electrical activity from one part of the brain to other parts. In many people with epilepsy, this activity begins from a well-defined focal point, which can be identified by electrical testing. Surgical treatment of focal-origin seizures involves removal of the brain region containing the focal point, usually in a procedure called temporal lobectomy. In other people, no focal point is found, or there may be too many to remove individually. These patients are most likely to receive corpus callosotomy.
The purpose of a corpus callosotomy is to prevent spreading of seizure activity from one half of the brain to the other. The brain is divided into two halves, or hemispheres, that are connected by a thick bundle of nerve fibers, the corpus callosum. When these fibers are cut, a seizure that begins in one hemisphere is less likely to spread to the other. This can reduce the frequency of seizures significantly.
The initial surgery may cut the forward two-thirds of the corpus callosum, leaving the rest intact. If this does not provide sufficient seizure control, the remaining portion may be cut.
Demographics
Corpus callosotomy is most often performed for children with "drop attacks," or atonic seizures, in which a sudden loss of muscle tone causes the child to fall to the floor. It is also performed in people with uncontrolled generalized tonic-clonic, or grand mal, seizures, or with massive jerking movements. Of the 20,000 to 70,000 people in the United States considered candidates for any type of epilepsy surgery, approximately 5,000 receive surgery per year. Between 1985 and 1990, more than 800 corpus callosotomies were performed, and the number has increased since then. Corpus callosotomy is performed by a special neurosurgical team, at a regional epilepsy treatment center.
Description
During corpus callosotomy, the patient is under general anesthesia, lying on the back. The head is fixed in place with blunt pins attached to a rigid structure. The head is shaved either before or during the procedure.
Incisions are made in the top of the skull to remove a flap of bone, exposing the brain. The outer covering is cut, and the two hemispheres are pulled slightly apart to expose the corpus callosum. The fibers of the corpus callosum are cut, taking care to avoid nearby arteries and ventricles (fluid-filled cavities in the brain).
Once the cut is made and any bleeding is controlled, the brain covering, bone, and scalp are closed and stitched.
Diagnosis/Preparation
The candidate for any type of epilepsy surgery will have had a wide range of tests prior to surgery. These include electroencephalography (EEG), in which electrodes are placed on the scalp, on the brain surface, or within the brain to record electrical activity. EEG is used to attempt to locate the focal point(s) of the seizure activity.
Several neuroimaging procedures are used to obtain images of the brain. These may reveal structural abnormalities that the neurosurgeon must be aware of. These procedures may include magnetic resonance imaging (MRI), x rays, computed tomography (CT) scans, or positron emission tomography (PET) imaging.
Neuropsychological tests may be done to provide a baseline against which the results of the surgery are measured. A Wada test may also be performed. In this test, a drug is injected into the artery leading to one half of the brain, putting it to sleep, allowing the neurologist to determine where language and other functions in the brain are localized, which may be useful for predicting the result of the surgery.
Aftercare
The patient remains in the hospital for about a week, possibly more depending on any complications that have occurred during surgery and on the health of the patient. There may be some discomfort afterwards. Tylenol with codeine may be prescribed for pain. Bending over should be avoided if possible, as it may lead to headache in the week or so after the procedure. Ice packs may be useful for pain and itchiness of the sutures on the head. Another several weeks of convalescence at home are required before the patient can resume normal activities. Heavy lifting or straining may continue to cause headaches or nausea, and should be avoided until the doctor approves. A diet rich in fiber can help avoid constipation, which may occur following surgery. Patients remain on anti-seizure medication at least for the short term, and may continue to require medication.
Risks
There is a slight risk of infection or hemorrhage from the surgery, usually less than 1%. Disconnection of the two hemispheres of the brain can cause some neuropsychological impairments such as decreased spontaneity of speech (it may be difficult to bring the right words into one's mind) and decreased use of the non-dominant hand. These problems usually improve over time. Complete cutting of the corpus callosotomy produces more long-lasting, but very subtle deficits in connecting words with images. These are usually not significant, or even noticed, by the patient.
Normal results
Patients typically experience a marked reduction in number and severity of seizures, with a small percentage of people becoming seizure free. Drop attacks may be eliminated completely in approximately 70% of patients. Other types of seizure are also reduced by 50% or more from corpus callosotomy surgery.
Morbidity and mortality rates
Serious morbidity or mortality occurs in 1% or less of patients. Combined major and minor complication rates are approximately 20%.
Alternatives
Newer anti-seizure medications have partially replaced corpus callosotomy. Focal epilepsy is treated with focal surgery such as temporal lobectomy or hemispherectomy . Vagus nerve stimulation is an alternative for some patients.
See also Hemispherectomy; Vagal nerve stimulation.
Resources
books
devinsky, o. a guide to understanding and living with epilepsy. philadelphia: ea davis, 1994.
organizations
epilepsy foundation. <www.epilepsyfoundation.org>.
Richard Robinson
WHO PERFORMS THE PROCEDURE AND WHERE IS IT PERFORMED?
Corpus callosotomy is performed by a neurosurgeon in a hospital operating room .
QUESTIONS TO ASK THE DOCTOR
- Are there any drugs that we haven't tried that may be effective?
- How long until I can return to school or work?
- Am I a candidate for any other epilepsy surgery?
split brain
If such a patient's hands are obscured from his view and an object is placed in the right hand, he can name it easily. Conversely, if it is placed in the left hand, the patient is unable to identify it verbally. Given an array of items to choose from, however, the left hand is immediately able to pick out this same item. Since initiation of left-hand movement occurs in the right hemisphere, this indicates that the right hemisphere has knowledge about the object but is unable to name it.
Over the years, more sophisticated testing procedures have taken advantage of the contralateral organization of various perceptual systems, such as the visual system, to explore the specialized functions of the two hemispheres. These studies have resulted in remarkable insights into the specialized capacities of each disconnected hemisphere. They have also revealed how the two hemispheres work in concert in the normal brain to provide seamless integration of sensory, motor, and cognitive functions.
Split-brain patients behave in ways that were to a large extent predicted by classical neurology. For example, the most striking aspect of the split-brain syndrome is that the left hemisphere has access to speech and the right hemisphere does not. The left hemisphere's specialization for language was already long established, based on data from patients with unilateral brain damage. Although the effects of disconnection on language were therefore not unexpected, it was surprising to discover the extent to which the left hemisphere was specialized for problem-solving of all kinds. Indeed, not only could it, and it alone, solve a wide range of cognitive problems, it also possessed a special device that has been called the ‘interpreter’. In brief, this was revealed by presenting two pictures, one to each half brain. For example, a picture of a snow scene was presented (from the left field of vision) to the right hemisphere of a split-brain patient. The non-talking right hemisphere had four cards to choose from, one of which was a shovel. At the same time the left hemisphere was shown a chicken claw and its four choices included a picture of a chicken. Following presentation of these pictures the patient was allowed to choose between the eight possible pictures. The left hand, governed by the right hemisphere, chose the shovel and the right hand, governed by the left hemisphere, chose the chicken. When asked by the experimenter why he had responded in that manner, the speaking left hemisphere said, ‘Oh, the chicken claw goes with the chicken, and you need a shovel to clean out the chicken shed.’ The left hemisphere in fact did not know why the left hand chose the shovel. The left brain observed what the right hand was doing and came up with a theory that explained away an action.
The right hemisphere appears to lack the interpretive capacities of the left and consequently is markedly impoverished in problem solving. Nevertheless, the right brain has it own specializations. The right hemisphere is superior to the left in a wide range of perceptual skills, such as grouping of visual elements into a whole picture. Early demonstrations of this involved copying drawings with each hand separately. With their hands obscured from view, right-handed split-brain patients were able to produce reasonable copies with their left hands but not with their right. The drawings made by the right hand contained details of the original pictures but had little or no spatial coherence. More recent research has revealed the right hemisphere's superiority in making orientation judgments, remembering unknown, upright faces, and a host of other visual tasks.
Investigations into the realms of language and perception clearly reveal the functional differences between the two hemispheres. Studies on memory and attention, however, provide insights into the ways in which the two hemispheres work together in an intact brain. Memory research with split-brain patients suggests that the two hemispheres each provide a unique input into storing information and later retrieving it. The left hemisphere interpreter is thought to be continually generating theories to explain the information it is currently processing. As a result, this hemisphere is particularly suited to getting the ‘gist’ of an event. This interpretive function, however, means that the left hemisphere often makes errors in recalling details of an event. The more literal right hemisphere does not make inferences and generalizations about incoming information, so this hemisphere is much less likely to make factual errors. The two hemispheres therefore work together to provide a system which is capable of accurately recalling details while still allowing for elaboration and inferences about the world.
Attention is something else that involves interaction between the two hemispheres. Both hemispheres are able to orient reflexively to external stimuli, and this focusing of attention occurs independently in each hemisphere. Voluntary orienting, however, appears to involve a single shared resource. This is illustrated by experiments that require each hemisphere to be performing a task independently of the other; then, when one hemisphere has a difficult task, the performance of the other hemisphere on a separate task is impaired. If the task of the first hemisphere becomes relatively easy, however, the performance of the other hemisphere improves markedly. Thus although the two hemispheres co-operate in many aspects of neural functioning, in the realm of voluntary control of attention the two hemispheres appear to compete. Studies that demand this kind of hemispheric competition have revealed that control over voluntary attention seems to be preferentially lateralized to the left hemisphere.
In summary, studies with split-brain patients have provided invaluable insights into the specialized functions of the two hemispheres and the ways in which they interact to enable myriad perceptual and cognitive functions.
Michael Gazzaniga, and Paul M. Corballis
See also brain; language and the brain.
Corpus Callosotomy
Corpus callosotomy
Definition
Corpus callosotomy is a treatment for epilepsy , in which a group of fibers connecting the two sides of the brain, called the corpus callosum, is cut.
Purpose
Corpus callosotomy is used to treat epilepsy that is unresponsive to drug treatments. A person with epilepsy may be considered good candidate for one type of epilepsy surgery or another if he or she has seizures that are not adequately controlled by drug therapy, and has tried at least two (perhaps more, depending on the treatment center's guidelines) different anti-epileptic drugs.
The seizures of epilepsy are due to unregulated spreading of electrical activity from one part of the brain to other parts. In many people with epilepsy, this activity begins from a well-defined focal point, which can be identified by electrical testing. Surgical treatment of focal-origin seizures involves removal of the brain region containing the focal point, usually in a procedure called temporal lobectomy. In other people, no focal point is found, or there may be too many to remove individually. These patients are most likely to receive corpus callosotomy.
The purpose of a corpus callosotomy is to prevent spreading of seizure activity from one half of the brain to the other. The brain is divided into two halves, or hemispheres, that are connected by a thick bundle of nerve fibers, the corpus callosum. When these fibers are cut, a seizure that begins in one hemisphere is less likely to spread to the other. This can reduce the frequency of seizures significantly.
The initial surgery may cut the forward two-thirds of the corpus callosum, leaving the rest intact. If this does not provide sufficient seizure control, the remaining portion may be cut.
Corpus callosotomy is most often performed for children with "drop attacks," or atonic seizures, in which a sudden loss of muscle tone causes the child to fall to the floor. It is also performed in people with uncontrolled generalized tonic-clonic, or grand mal, seizures, or with massive jerking movements. Of the 20,000 to 70,000 people in the United States considered candidates for any type of epilepsy surgery, approximately 5,000 receive surgery per year. Between 1985 and 1990, more than 800 corpus callosotomies were performed, and the number has increased since then. Corpus callosotomy is performed by a special neurosurgical team, at a regional epilepsy treatment center.
Description
During corpus callosotomy, the patient is under general anesthesia, lying on the back. The head is fixed in place with blunt pins attached to a rigid structure. The head is shaved either before or during the procedure.
Incisions are made in the top of the skull to remove a flap of bone, exposing the brain. The outer covering is cut, and the two hemispheres are pulled slightly apart to expose the corpus callosum. The fibers of the corpus callosum are cut, taking care to avoid nearby arteries and ventricles (fluid-filled cavities in the brain).
Once the cut is made and any bleeding is controlled, the brain covering, bone, and scalp are closed and stitched.
Preparation
The candidate for any type of epilepsy surgery will have had a wide range of tests prior to surgery. These include electroencephalography (EEG), in which electrodes are placed on the scalp, on the brain surface, or within the brain to record electrical activity. EEG is used to attempt to locate the focal point(s) of the seizure activity.
Several neuroimaging procedures are used to obtain images of the brain. These may reveal structural abnormalities that the neurosurgeon must be aware of. These procedures may include magnetic resonance imaging (MRI) , x rays, computed tomography (CT ) scans , or positron emission tomography (PET) imaging.
Neuropsychological tests may be done to provide a baseline against which the results of the surgery are measured. A Wada test may also be performed. In this test, a drug is injected into the artery leading to one half of the brain, putting it to sleep, allowing the neurologist to determine where language and other functions in the brain are localized, which may be useful for predicting the result of the surgery.
Aftercare
The patient remains in the hospital for about a week, possibly more depending on any complications that have occurred during surgery and on the health of the patient. There may be some discomfort afterwards. Tylenol with codeine may be prescribed for pain . Bending over should be avoided if possible, as it may lead to headache in the week or so after the procedure. Ice packs may be useful for pain and itchiness of the sutures on the head. Another several weeks of convalescence at home are required before the patient can resume normal activities. Heavy lifting or straining may continue to cause headaches or nausea, and should be avoided until the doctor approves. A diet rich in fiber can help avoid constipation, which may occur following surgery. Patients remain on anti-seizure medication at least for the short term, and may continue to require medication.
Risks
There is a slight risk of infection or hemorrhage from the surgery, usually less than 1%. Disconnection of the two hemispheres of the brain can cause some neuropsychological impairments such as decreased spontaneity of speech (it may be difficult to bring the right words into one's mind) and decreased use of the non-dominant hand. These problems usually improve over time. Complete cutting of the corpus callosotomy produces more long-lasting, but very subtle deficits in connecting words with images. These are usually not significant, or even noticed, by the patient.
Serious morbidity or mortality occurs in 1% or less of patients. Combined major and minor complication rates are approximately 20%.
Normal results
Patients typically experience a marked reduction in number and severity of seizures, with a small percentage of people becoming seizure free. Drop attacks may be eliminated completely in approximately 70% of patients. Other types of seizure are also reduced by 50% or more from corpus callosotomy surgery.
Resources
BOOKS
Devinsky, O. A Guide to Understanding and Living with Epilepsy. Philadelphia: EA Davis, 1994.
ORGANIZATIONS
Epilepsy Foundation. <www.epilepsyfoundation.org>.
Richard Robinson
Rosalyn Carson-DeWitt, MD