Epilepsy Surgery

Epilepsy Surgery

Surgery is an option in treatment of patients with intractable epilepsy, which cannot be controlled with medication adequately. If your seizures originate from an identifiable focus in the brain, you may be a candidate for resective surgery.

The purpose of the surgery is to remove abnormal part of the brain which is considered epileptic (source of the seizures). The pre-operative work up is comprehensive. You need to go through a pre-surgical evaluation to be identified as a surgical candidate or not. The outcome and seizure freedom after surgery depends on multiple factors, most important ones are epilepsy syndrome type, underlying pathology, surgical techniques and others.

What Are The Steps In Pre-Operative Evaluation?

  1. Obtaining necessary and optimal clinical information about your seizures and epilepsy syndrome.
  2. Classifying your epilepsy syndrome with EEG, clinical description of your seizures, and neuro-imaging such as magnetic resonance imaging of brain to localize the abnormal area, possible seizure focus.
  3. To identify the focus of your seizures by performing video EEG monitoring in the hospital setting at epilepsy monitoring units(EMUs). By this way your seizures will be captured and your seizure type and epilepsy syndrome will be classified. Also if possible the epileptic focus will be identified.
  4. Baseline neuropsychological evaluation will provide the information about your cognition and emotional functions. Sometimes it can find out a certain region of the brain which may not function well. That area may be the origin of your seizures. It can be used as reference point for postsurgical evaluation.
  5. WADA test or intracranial amytal test is used to identify which side is responsible for language. It also assesses the memory function of temporal lobes.
  6. Intracranial video EEG monitoring is performed when video EEG monitoring does not provide enough information about the origin and focus of seizures. It is performed by using intracranial electrodes as grids and/or strips, depth electrodes with enough coverage over the suspected area of origin of seizures.
  7. SPECT (Single photon emission computed tomography) scans find the seizure focus by measuring cerebral blood flow. During a seizure there is selectively increased blood flow in the seizure focus. As seizure starts, the radioactive tracer has to be given very early in the seizure to localize the area of seizure focus. It helps to localize seizure focus in difficult cases but it has to be done at hospital settings due to requirements of specially trained personnel.
  8. PET (Positron emission tomography) scans measure brain metabolism. Areas of seizure focus will require less energy, with decreased uptake of radioactive tracers. It can aid in deciding the seizure focus in surgical cases.

Surgical Techniques

  1. Focal cortical resection
  2. Anterior temporal lobectomy
  3. Corpus callosotomy
  4. Multiple subpial transection
  5. Hemispherectomy
  6. Vagus nerve stimulation and other devices

Focal cortical resection:

If an area of the brain is identified as the cause of seizures, focal resection is considered. But that area of the brain should not be an eloquent region. It should not carry important functions such as language, motor control, vision, or sensation. Removal of the area should not cause important permanent impairments. Certain tests can be done to find the functions of the region and the amount of impairment after resection. These tests are functional MRI and cortical motor and language mapping of the region with intracranial electrodes before resection if the area is or close to eloquent regions in the brain.

Anterior temporal resection:

If the seizures originate from the medial part of temporal lobe, this technique is used. The anterior part of temporal lobe is removed to provide better seizure control. The surgeon usually removes the lobe to a certain distance from the tip. Some surgeons may prefer to resect only the medial structures amygdala and hippocampus to cause less post surgical impairment and to preserve the language area if the surgery involves left temporal lobe.  That technique is called amygdalohippocampectomy.

Memory and language are very important functions of temporal lobe. Memory is one of the main functions of temporal lobes. With many years of seizures, patients with temporal lobe epilepsy already develop memory disturbances. For this reason, postsurgical memory disturbance may be minimal. To test the residual function and predict postsurgical impairment, WADA test is very helpful.

Corpus Callosotomy:

It was initially performed in 1939. In this technique the goal is to separate one hemisphere form another by cutting through the large bundle of connection fibers between these hemispheres. This fiber bundle structure is called corpus callosum. By this way seizure starting in one hemisphere will not spread to another therefore the patient will not have generalized seizures. It is successful in decreasing frequency of seizures with sudden loss of body tone, atonic seizures, tonic seizures, and generalized tonic clonic seizures. The patients will not fall during the seizures and will have less injuries. However corpus callosotomy does not make patients seizure free.

Hemispherectomy:

It is considered if seizures originate from large area of the hemisphere. It is usually caused by significant damage to one hemisphere such as birth trauma, malformations, strokes in utero, tuberous sclerosis, and Rasmussen encephalitis. This surgery is associated with significant residual deficits such as weakness, numbness, decreased vision, language and memory disturbance.

Nowadays to minimize the deficits, modified hemispherectomy is preferred. It involves separating upper lobes from deep central areas and from the other hemisphere. Upper lobes with blood supply area preserved on the other hand, the deep structures with corpus callosum are removed.

Multiple Subpial Transections:

If the seizure focus occupies an eloquent cortex, it cannot be removed.  Instead this technique was developed. It involves putting cuts parallel to each other over the cortex, being perpendicular to the long axis of the gyrus of the brain lobe. Postsurgical success varies and cannot be predicted. It can decrease the seizure frequency but unlikely it will provide seizure freedom. And its success can also be temporary.

Vagus Nerve Stimulator:

Vagus nerve stimulator (VNS) is a device that has been used in treatment of epilepsy.

It is designed to treat seizures by producing electrical signals transmitted to the brain through vagus nerve. It has been shown to decrease seizure frequency in humans.

VNS is an FDA approved electrical stimulation device to treat seizures. It is preferred in patients with refractory seizures but cannot be considered as surgical candidates. Also commonly used in patients who already have had brain surgery but still suffer from  refractory seizures.

VNS has two parts; generator (pacemaker) and wire. For the device insertion, two surgical incisions are made, one to implant the generator over the anterior left upper chest wall, the other one to wind the wire around vagus nerve on the left side of neck. VNS insertion is short procedure, taking about few hours. It is usually done as ambulatory surgery. The patient can go home the same day.

VNS is turned on two weeks after implantation. The interrogation and programming are done by the physician. The generator delivers stimulation automatically. VNS also has a magnet. If the magnet is wiped over the generator, it can cause generation of  extra stimulation by the device to stop seizures. The patient and families are instructed to wipe magnet over the generator when the patient feels aura or prodromal symptoms of seizures.

The other devices such as deep brain stimulation and neuropace have been used in clinical trials and have not been approved in the US yet.

Surgical Complications

Like any other type of surgery, the most common complications are bleeding and infection. This risk is about 1-2%. But these complications can be life threatening.

After brain surgeries, there may be leakage of cerebrospinal fluid through dura. It can cause persistent headaches and fluid collection under the scalp. This may require another surgery to stop leakage.

During the surgery nearby areas can be affected due to disturbed blood flow. It can manifest as a stroke. The patient may have motor and sensory symptoms or difficulty with language and vision. The symptoms depend on the location of surgery and proximity to eloquent regions.

Memory disturbance and loss of vision in the upper quadrants of visual fields can be seen after ATR. Psychiatric complications can also happen after ATR. It can vary from anxiety to psychosis.

Corpus callosotomy can cause lower extremity weakness which is usually temporary.  Also some patients may have disconnection syndrome such as trouble with following commands to perform certain tasks using arm, having trouble to control legs and arms from doing unintentional activities (Alien limb).

Hemispherectomy can cause significant motor and sensory function, vision loss on the opposite side of the surgery. The complications can be very debilitating, resulting in lower quality of life and functional status.

What Happens After Surgery?

Seizure outcome after surgery depends on epilepsy syndrome, type of surgical technique, and type of underlying pathology in the brain causing seizure. Seizure freedom or decrease seizure frequency can happen. Occasionally some patients may experience worsening of seizure control.

Surgery can be curative in resection of focal benign tumors. It may provide seizure freedom in about 90% of patients in 1 year after surgery. This is followed by antero-medial temporal lobe resection (ATR). ATR can provide seizure freedom about 65-80% in 1 year after surgery. After corpus callosotomy about 70-80% of patients experience around 50% decrease in seizure frequency. Usually tonic, atonic and generalized tonic clonic seizures decrease more than other seizure types after this procedure. Seizure freedom after hemispherectomy also depends on underlying syndrome and pathology.

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