The first examples of corpus callosotomy were performed in the 1940s by Dr. William P. van Wagenen; the corpus callosum is a fibre bundle of about 300 million fibrein the human brain that connects the two cerebral hemispheres. The interhemispheric functions of the corpus callosum include the integration of perceptual, cognitive, learned, and volitional information.
The role of the corpus callosum in epilepsy 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. Seizure surgery involves:
- Removing tissue from the area where the seizures begin.
- Interrupting the nerve pathways where the impulses travel
A corpus callosotomy is an operation that severs (cuts) the corpus callosum, interrupting the spread of seizures from hemisphere to hemisphere. Seizures generally do not completely stop after this procedure (they continue on the side of the brain in which they originate). However, the seizures usually become less severe, as they cannot spread to the opposite side of the brain.
Indications
- For uncontrolled generalized seizures, especially atonic seizures (drop attacks).
- Generalized tonic-clonic seizures and partial seizures that rapidly secondarily generalize and it is not possible to identify a single epileptic focus.
- Medically refractory: Already tried at least 2 of the standard medicines without success or side effects.
Patients of any age, including infants, may be considered for surgery if other criteria are met.
Contraindications
- Progressive neurological or medical disease might be an absolute or relative contraindication to corpus callosotomy.
- Mental retardation is not a contraindication to corpus callosotomy. In a study of children with severe mental retardation, total callosotomy was performed with highly favorable results and insignificant morbidity.
Decision making
- Correct diagnosis of seizure disorder
- Choice of surgical intervention
- History of seizure control with drugs and other measures.
- Can the condition get better without surgery?
- Can it get worse without surgery?
- Do the benefits outweigh the risks?
Preoperative evaluation
- Patient and family history.
- Detailed neurological examination.
- Baseline EEG
- CT scan
- MRI
- Scalp seizure monitoring with simultaneous Video/EEG recording and monitoring.
- Neuropsychological evaluation
- PET scans
- SPECT scans
- Video/EEG monitoring using electrodes placed surgically within or around the brain. This may be needed before the final seizure surgery can be done. In some cases, a separate operation is necessary to place the electrodes in order to locate seizure sites deep in the brain.
- WADA test if indicated.
Note
- EEG (Electroencephalogram) involves recording a patient’s brain waves. An EEG records and analyzes any seizure discharge that occurs in the brain waves.
- CT (computerized tomography) and MRI (magnetic resonance imaging) scans help in determining if there is a lesion, malformation, or tumor producing seizures.
- PET (positron emission tomography) and SPECT (single photon emission computer tomography) scans test brain metabolism, chemistry, or blood flow. They use specially prepared radioisotopes that are safe for medical diagnostic use. They help in localizing a seizure focus.
Surgical procedure: CORPUS CALLOSUM SECTION (CORPUS CALLOSTOMY)
A corpus callosotomy requires exposing the brain using a procedure called a craniotomy. After the patient is put to sleep with anaesthesia, the surgeon makes an incision in the scalp, removes a piece of bone and pulls back a section of the dura, the tough membrane that covers the brain. This creates a “window” in which the surgeon inserts special instruments for disconnecting the corpus callosum. The surgeon gently separates the hemispheres to access the corpus callosum. Surgical microscopes are used to give the surgeon a magnified view of brain structures.
