A corpus callosotomy () is a palliative surgical procedure for the treatment of medically refractory

epilepsy Epilepsy is a group of Non-communicable disease, non-communicable Neurological disorder, neurological disorders characterized by a tendency for recurrent, unprovoked Seizure, seizures. A seizure is a sudden burst of abnormal electrical activit ...

. The procedure was first performed in 1940 by William P. van Wagenen. 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 ...

is cut through, in an effort to limit the spread of epileptic activity between the two halves of the brain. Although the corpus callosum is the largest

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

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

anterior Standard anatomical terms of location are used to describe unambiguously the anatomy of humans and other animals. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position pro ...

and posterior commissures. After the operation, however, the brain often struggles to send messages between hemispheres, which can lead to side effects such as speech irregularities, disconnection syndrome, and alien hand syndrome.

History

The first instances of corpus callosotomy were performed in the 1940s by William P. van Wagenen, who co-founded and served as president of the American Association of Neurological Surgeons. Attempting to treat epilepsy, van Wagenen studied and published the results of his surgeries, including the split-brain outcomes for patients. Most of the surgeries involved a partial division of the corpus callosum and resulted in improvements of seizure control in all patients. Wagenen's work preceded the 1981

Nobel Prize The Nobel Prizes ( ; ; ) are awards administered by the Nobel Foundation and granted in accordance with the principle of "for the greatest benefit to humankind". The prizes were first awarded in 1901, marking the fifth anniversary of Alfred N ...

-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. The surgery is a palliative treatment method for many forms of epilepsy, including atonic seizures, 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 symptoms of inattention, hyperactivity, impulsivity, and emotional dysregulation that are excessive and pervasive, impairing in multiple con ...

, EEG 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 medically induced loss of consciousness that renders a patient unarousable even by painful stimuli. It is achieved through medications, which can be injected or inhaled, often with an analgesi ...

, an incision will allow for a

craniotomy A craniotomy is a surgery, surgical operation in which a bone flap is temporarily removed from the Human skull, skull to access the Human brain, brain. Craniotomies are often critical operations, performed on patients who are suffering from brain ...

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. Afterward, the dura is closed and the portion of cranium 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 has been documented by population-based studies in Europe. In the UK and Sweden, 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 , "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 nervous system, which comprises the brain, the s ...

or medical disease might be an absolute or relative contraindication to corpus callosotomy.

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

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 (spelled fibre in British English; from ) 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 inco ...

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. Its interhemispheric functions include the integration of perceptual,

cognitive Cognition is 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 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

Side effects

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

speech Speech is the use of the human voice as a medium for language. Spoken language combines vowel and consonant sounds to form units of meaning like words, which belong to a language's lexicon. There are many different intentional speech acts, suc ...

irregularities. For some patients, sectioning may be followed by a brief spell of mutism. A long-term side effect may be an inability to engage in spontaneous speech. In addition, the resultant split-brain prevents some patients from following verbal commands that require the use of their non-dominant hand. Disconnection syndrome is another well-known side effect of the surgery. This occurs due to the brain's inability to transfer information between the hemispheres. One characteristic symptom is the "crossed-avoiding reaction", which is observed when one hemisphere does not respond to visual or sensory (e.g., touch, pressure, or pain) stimuli presented to the opposite side. For instance, when an object is shown in the patient's right visual field, the left hemisphere (typically language-dominant) processes this information, allowing the patient to name the object easily. However, if the same object is shown in the left visual field, the right hemisphere perceives it, but the information does not transfer to the left (verbal) hemisphere. Consequently, while the patient cannot verbally identify the object, they are still able to select it with their left hand. Another complication is alien hand syndrome, in which the affected person's hand appears to take on a mind of its own. In one described incident, the patient grabbed their throat with their left hand and struggled to remove, as they had no control over it.

Cognitive impairments Cognition is 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, i ...

may also be seen. Other symptoms may occur after the operation but generally go away on their own, such as scalp numbness, feeling tired or depressed, headaches, and difficulty speaking, remembering things, or finding words.

Alternatives

Epilepsy is also treated by a less invasive process called vagus nerve stimulation. 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 a gas). In electrochemical cells, electrodes are essential parts that can consist of a varie ...

implanted around the left vagus nerve within the

carotid sheath The carotid sheath is a condensation of the deep cervical fascia enveloping multiple vital neurovascular structures of the neck, including the common and internal carotid arteries, the internal jugular vein, the vagus nerve (CN X), and ansa c ...

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).

References

External links

Details of procedure
at epilepsy.com

{{Central nervous system tests and procedures Neurosurgical procedures Epilepsy