Corpus callosotomy is a palliative surgical procedure for the treatment of medically refractory

epilepsy Epilepsy is a group of non-communicable neurological disorders characterized by recurrent epileptic seizures. Epileptic seizures can vary from brief and nearly undetectable periods to long periods of vigorous shaking due to abnormal electrica ...

. In this procedure the

corpus callosum The corpus callosum (Latin for "tough body"), also callosal commissure, is a wide, thick nerve tract, consisting of a flat bundle of commissural fibers, beneath the cerebral cortex in the brain. The corpus callosum is only found in placental m ...

is cut through in an effort to limit the spread of epileptic activity between the two halves of the brain. After the operation the brain has much more difficulty sending messages between the hemispheres. Although the corpus callosum is the largest

white matter White matter refers to areas of the central nervous system (CNS) that are mainly made up of myelinated axons, also called tracts. Long thought to be passive tissue, white matter affects learning and brain functions, modulating the distribution ...

tract connecting the hemispheres, some limited interhemispheric communication is still possible via the

anterior commissure The anterior commissure (also known as the precommissure) is a white matter tract (a bundle of axons) connecting the two temporal lobes of the cerebral hemispheres across the midline, and placed in front of the columns of the fornix. In most exist ...

and

posterior commissure The posterior commissure (also known as the epithalamic commissure) is a rounded band of white fibers crossing the middle line on the dorsal aspect of the rostral end of the cerebral aqueduct. It is important in the bilateral pupillary light refle ...

. "Efficacy and relatively low permanent morbidity in corpus callosotomy for medically intractable epilepsy have been demonstrated by more than six decades of experience. In addition to seizure reduction, behavior and quality of life may improve."

History

The first examples of corpus callosotomy were performed in the 1940s by Dr. William P. van Wagenen, who co-founded and served as president of the

American Association of Neurological Surgeons The American Association of Neurological Surgeons (AANS) is a scientific and educational association focused on advancing the specialty of neurological surgery. The organization has over 8,000 members around the world. It is one of the five Conti ...

. Attempting to treat epilepsy, van Wagenen studied and published the results of his surgeries, including the

split-brain Split-brain or callosal syndrome is a type of disconnection syndrome when the corpus callosum connecting the two hemispheres of the brain is severed to some degree. It is an association of symptoms produced by disruption of, or interference wit ...

outcomes for patients. Wagenen's work preceded the 1981 Nobel Prize-winning research of Roger W. Sperry by two decades. Sperry studied patients who had undergone corpus callosotomy and detailed their resulting split-brain characteristics. Improvements to surgical techniques, along with refinements of the indications, have allowed van Wagenen's procedure to endure; corpus callosotomy is still commonly performed throughout the world. Currently, the surgery is a

palliative treatment Palliative care (derived from the Latin root , or 'to cloak') is an interdisciplinary medical caregiving approach aimed at optimizing quality of life and mitigating suffering among people with serious, complex, and often terminal illnesses. Wit ...

method for many forms of epilepsy, including

atonic seizure An atonic seizure (also called drop seizure, akinetic seizure, astatic seizure, or drop attack) is a type of seizure that consists of partial or complete loss of muscle tone that is caused by temporary alterations in brain function. These seizures ...

s, generalized seizures, and Lennox-Gastaut syndrome. In a 2011 study of children with intractable epilepsy accompanied by

attention deficit disorder Attention deficit hyperactivity disorder (ADHD) is a neurodevelopmental disorder characterised by excessive amounts of inattention, hyperactivity, and impulsivity that are pervasive, impairing in multiple contexts, and otherwise Development ...

EEG Electroencephalography (EEG) is a method to record an electrogram of the spontaneous electrical activity of the brain. The biosignals detected by EEG have been shown to represent the postsynaptic potentials of pyramidal neurons in the neocortex ...

showed an improvement to both seizures and attention impairments following corpus callosotomy.

Typical procedure

Prior to surgery, the patient's head must be partially or completely shaven. Once under

general anesthesia General anaesthesia (UK) or general anesthesia (US) is a medically induced loss of consciousness that renders the patient unarousable even with painful stimuli. This effect is achieved by administering either intravenous or inhalational general ...

, an incision will allow for a

craniotomy A craniotomy is a surgical operation in which a bone flap is temporarily removed from the skull to access the brain. Craniotomies are often critical operations, performed on patients who are suffering from brain lesions, such as tumors, blood clots ...

to be performed. Then sectioning will occur between the two hemispheres of the brain. For a partial callosotomy, the anterior two-thirds of the corpus callosum are sectioned, and for a complete callosotomy, the posterior one-third is also sectioned. After sectioning, the dura is closed and the portion of

cranium The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, the ...

is replaced. The scalp is then closed with sutures. Endoscopic corpus callosotomy has been employed with blood loss minimized during the surgical procedure.

Indications

Corpus callosotomy is intended to treat patients who have epilepsy and the resultant chronic seizures. The diminished life expectancy associated with epilepsy patients has been documented by population-based studies in Europe. In the

United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the continental mainland. It comprises England, Scotland, Wales and North ...

and

Sweden Sweden, formally the Kingdom of Sweden,The United Nations Group of Experts on Geographical Names states that the country's formal name is the Kingdom of SwedenUNGEGN World Geographical Names, Sweden./ref> is a Nordic country located on ...

, the relative mortality rate of epileptic patients (patients whose epilepsy was not under control from medical or other surgical therapies, and who continued to have the disease) increased two- and threefold, respectively. In the vast majority of cases, corpus callosotomy abolishes instance of seizures in the patient.

Contraindications

Although it varies from patient to patient, a progressive

neurological Neurology (from el, νεῦρον (neûron), "string, nerve" and the suffix -logia, "study of") is the branch of medicine dealing with the diagnosis and treatment of all categories of conditions and disease involving the brain, the spinal ...

or medical disease might be an absolute or relative

contraindication In medicine, a contraindication is a condition that serves as a reason not to take a certain medical treatment due to the harm that it would cause the patient. Contraindication is the opposite of indication, which is a reason to use a certain tre ...

to corpus callosotomy.

Intellectual disability Intellectual disability (ID), also known as general learning disability in the United Kingdom and formerly mental retardation,Rosa's Law, Pub. L. 111-256124 Stat. 2643(2010). is a generalized neurodevelopmental disorder characterized by signifi ...

is not a contraindication to corpus callosotomy. In a study of children with a severe intellectual disability, total callosotomy was performed with highly favorable results and insignificant morbidity.

Neuroanatomical background

Corpus callosum anatomy and function

The corpus callosum is a fiber bundle of about 300 million

fibers Fiber or fibre (from la, fibra, links=no) is a natural or artificial substance that is significantly longer than it is wide. Fibers are often used in the manufacture of other materials. The strongest engineering materials often incorporate ...

in the human brain that connects the two

cerebral hemisphere The vertebrate cerebrum (brain) is formed by two cerebral hemispheres that are separated by a groove, the longitudinal fissure. The brain can thus be described as being divided into left and right cerebral hemispheres. Each of these hemispheres ...

s. The interhemispheric functions of the corpus callosum include the integration of

perceptual Perception () is the organization, identification, and interpretation of sense, sensory information in order to represent and understand the presented information or environment. All perception involves signals that go through the nervous ...

cognitive Cognition refers to "the mental action or process of acquiring knowledge and understanding through thought, experience, and the senses". It encompasses all aspects of intellectual functions and processes such as: perception, attention, thought, ...

, learned, and

volitional Volition may refer to: * Volition (psychology), the process of making and acting on decisions ** Coherent Extrapolated Volition, hypothetical choices and the actions collectively taken with more knowledge and ability * Volition (linguistics), a di ...

information.

Role in epileptic seizures

The role of the corpus callosum in

is the interhemispheric transmission of epileptiform discharges. These discharges are generally bilaterally synchronous in preoperative patients. In addition to disrupting this synchrony, corpus callosotomy decreases the frequency and amplitude of the epileptiform discharges, suggesting the transhemispheric facilitation of seizure mechanisms.

Drawbacks and criticisms

Side effects

The most prominent non-surgical complications of corpus callosotomy relate to

speech Speech is a human vocal communication using language. Each language uses Phonetics, phonetic combinations of vowel and consonant sounds that form the sound of its words (that is, all English words sound different from all French words, even if ...

irregularities. For some patients, sectioning may be followed by a brief spell of

mutism Muteness or mutism () is defined as an absence of speech while conserving or maintaining the ability to hear the speech of others. Mutism is typically understood as a person's inability to speak, and commonly observed by their family members, caregi ...

. A long-term side effect that some patients may have is an inability to engage in spontaneous speech. In addition, the resultant split-brain prevented some patients from following verbal commands that required use of their non-dominant hand. Another complication is alien hand syndrome, in which the affected person's hand appears to take on a mind of its own.

Cognitive impairments Cognitive deficit is an inclusive term to describe any characteristic that acts as a barrier to the cognition process. The term may describe * deficits in overall intelligence (as with intellectual disabilities), * specific and restricted defic ...

may be seen. (Other symptoms may occur after the operation, but generally go away on their own: Scalp numbness, feeling tired or depressed, headaches, difficulty speaking, remembering things, or finding words.)

Alternatives

Epilepsy is also currently treated by a less invasive process called

vagus nerve stimulation Vagus nerve stimulation (VNS) is a medical treatment that involves delivering electrical impulses to the vagus nerve. It is used as an add-on treatment for certain types of intractable epilepsy and treatment-resistant depression. Medical use VN ...

. This method utilizes an

electrode An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor, an electrolyte, a vacuum or air). Electrodes are essential parts of batteries that can consist of a variety of materials de ...

implanted around the left vagus nerve within the carotid sheath in order to send electrical impulses to the nucleus of the solitary tract. However, corpus callosotomy has been proven to offer significantly better chances of seizure freedom compared with vagus nerve stimulation (58.0% versus 21.1% reduction in atonic seizures, respectively). If a focal area in the brain is generating severe seizures, it can sometimes be removed.

References

External links

Detail on the procedure
from epilepsy.com

{{Central nervous system tests and procedures Neurosurgical procedures Epilepsy