Epilepsy surgery

Overview

Epilepsy surgery involves removing a part of the brain that is responsible for causing seizures.

This surgical approach is most beneficial when seizures consistently originate from the same area within the brain. It is not considered an initial treatment method. Instead, it becomes a consideration when a minimum of two anti-seizure medications have been ineffective in managing seizures.

Before deciding on epilepsy surgery as a viable option and determining the specific surgical procedure required, a series of diagnostic tests may be necessary.

Types

Epileptic seizures originate from abnormal activity in brain cells known as neurons. The surgical intervention required varies based on the neurons’ location initiating the seizures and the patient’s age. There are several surgical options:

• Resective surgery: This is the most frequently performed surgery for epilepsy, involving the removal of a portion of the brain. The procedure targets brain tissue in the region where seizures start, often due to a tumor, injury, or malformation, typically in one of the temporal lobes. The temporal lobes are crucial for managing visual memory, language understanding, and emotions.
• Laser interstitial thermal therapy (LITT): A less invasive alternative to resective surgery, LITT employs a laser to precisely eliminate a small section of brain tissue. The process is MRI-guided to ensure accuracy.
• Deep brain stimulation: This technique involves implanting a device deep within the brain that emits regular electrical impulses to interrupt the activity that leads to seizures. An magnetic resonance imaging (MRI) guides the placement, and the device’s generator is implanted in the chest.
• Corpus callosotomy: This operation involves either fully or partially severing the corpus callosum, the brain structure that connects the right and left brain hemispheres. It’s primarily used in children to manage seizure activity that spreads from one hemisphere to the other.
• Hemispherectomy: This drastic procedure involves removing one cerebral hemisphere and is usually reserved for children with seizures emanating from multiple locations within one hemisphere, often due to congenital conditions or issues arising in early infancy.
• Functional hemispherectomy: Similar to a hemispherectomy, this method focuses on severing the connecting nerves between the hemispheres rather than removing brain tissue. It is mainly used in pediatric cases.

Reasons for undergoing the procedure

Criteria for considering surgery:

• Drug-resistant epilepsy: Surgery is considered when at least two anti-seizure medications have failed to control seizures. This condition is often referred to as drug-resistant epilepsy or medically refractory epilepsy.
• Intolerable side effects: When the side effects of anti-seizure medications are severe and cannot be tolerated.
• Ineffectiveness of diet therapy: In cases where dietary approaches like the ketogenic diet do not help in controlling seizures.
• Severity and frequency of seizures: Surgery is an option when seizures are frequent, severe, and significantly impact quality of life.
• Underlying non-epileptic conditions: Surgery may be recommended if seizures are caused by conditions such as a brain tumor or arteriovenous malformation.

Success factors for epilepsy surgery:

• Localized seizure origin: Epilepsy surgery is most effective for individuals whose seizures originate and remain in one specific area of the brain.
• Safety and preservation of function: The surgery can be performed without causing new or worsening problems in critical functions like memory, speech, vision, and movement.

Risk

Different parts of the brain are responsible for various functions, and the potential risks associated with surgery vary based on the location and type of operation. The medical team will outline the specific risks involved in the procedure, as well as strategies to minimize the likelihood of complications. Possible risks can include:

• Bleeding.
• Infection.
• Headache
• Stroke.
• Language and memory issues that could hinder a person’s capacity to comprehend and utilize language.
• Visual impairment where the overlapping fields of vision in the eyes.
• Depression or other mood disorders that have the potential to damage social interactions.

Procedure

Healthcare professionals conduct pre-operative evaluations for all individuals, both children and adults, who are candidates for epilepsy surgery.

The objectives of these pre-operative evaluations include:

• Identifying the precise location in the brain where seizures originate, using a combination of tests.
• Assessing whether the area of brain tissue where seizures begin can be removed or if the connections between brain regions can be disrupted without causing harm.
• Understanding which essential functions are managed by the brain regions near the seizure’s origin.
• Estimating the surgery’s success in terms of reducing the frequency or severity of seizures or potentially eliminating them entirely.

Epilepsy surgery is a treatment option for those who have seizures that medication cannot control. Here’s an overview of the various surgical procedures available:

Surgical resection

In this approach, neurosurgeons remove specific brain tissue where seizures originate or the abnormal tissue causing seizures. Types include:

• Lesionectomy: Removal of lesions like tumors, cavernous hemangiomas, and arteriovenous malformations that cause seizures.
• Lobectomy: Removal of a brain lobe (frontal, temporal, parietal, occipital), with temporal lobectomy being the most common.
• Multilobar resection: Removal of parts of two or more brain lobes, considered when these areas do not involve vital functions.
• Hemispherectomy: Removal or disconnection of one brain hemisphere, typically for severe, uncontrollable seizures, often when the hemisphere is already damaged.

Surgical disconnection

These procedures cut communication between the seizure-generating area and the rest of the brain:

• Corpus callosotomy: Severing the corpus callosum to prevent seizures from spreading from one brain hemisphere to the other.
• Multiple subpial transections: Making shallow cuts in brain tissue to disrupt seizure-spreading nerve cell communication, considered when the seizure area cannot be removed safely.

Stereotactic radiosurgery

Uses 3D imaging to focus radiation on the target area, destroying the misfiring nerve cells causing seizures.

Laser interstitial thermal therapy

A minimally invasive method where a laser probe, guided by MRI, destroys nerve cells in the seizure site through heat.

Neuromodulation (implanted devices)

These involve devices implanted to control seizures without removing brain tissue:

• Vagus nerve stimulation: A device sends electrical pulses to the brain via the vagus nerve to disrupt seizure activity.
• Responsive neurostimulation: A device implanted in or on the brain tissue sends electrical impulses to stop seizures as they start.
• Deep brain stimulation: Involves implanting an electrode in the brain and a stimulator device in the chest, blocking nerve signals that may trigger seizures.

Each of these surgical options offers hope for better seizure control when medication is not effective, tailored to individual needs and the specifics of their epilepsy.

Before the procedure

When evaluating a candidate for epilepsy surgery at a specialized epilepsy center, the health care team conducts various tests to assess eligibility, determine the precise location for surgery, and understand the specific brain functions of that area. These evaluations can be outpatient or require hospitalization.

To identify the source of a seizure, standard tests include:

• Baseline electroencephalogram (EEG): Measures brain’s electrical activity through scalp-placed electrodes to suggest affected areas.
• Video EEG: Combines continuous EEG with video to record seizures, requiring hospitalization as seizure medications are adjusted.
• Magnetic resonance imaging (MRI): Uses magnetic fields and radio waves to create detailed brain images, identifying potential seizure causes like damaged cells or tumors.

Additional tests for precise seizure source localization:

• Invasive EEG monitoring: Surgically placed electrodes on or inside the brain for detailed monitoring, performed under unconsciousness.
• Video EEG with invasive electrodes: Similar to video EEG, but with surgically placed electrodes.
• Positron emission tomography (PET): Measures brain function in a seizure-free state, identifying seizure sources alone or combined with MRI.
• Single-photon emission computerized tomography (SPECT): Assesses brain blood flow during a seizure, indicating the seizure’s location.

To preserve critical brain functions during surgery, tests may include:

• Functional MRI (fMRI): Identifies active brain regions during specific tasks (e.g., listening, reading), pinpointing important functional areas.
• Wada test: Temporarily inactivates one brain hemisphere to test language and memory, determining language dominance.
• Brain mapping: Uses small surface electrodes for task-based electrical activity measurement when the patient is alert post-surgery.
• Magnetoencephalography (MEG): Analyzes brain’s magnetic fields to locate seizure sites, used alongside other data.

Neuropsychological Tests

These assess verbal, nonverbal learning, and memory functions, providing insights into the affected brain area and a baseline for post-surgery function comparison.

To minimize infection risk, the surgical area on the skull is shaved or clipped short. A flexible tube is inserted into a vein for IV fluids, anesthetics, or medication administration during surgery.

During the procedure

First, your healthcare provider will shave the part of your head where they’ll perform the surgery, and your anesthesiologist will administer anesthesia to ensure you remain asleep throughout the procedure, with close monitoring of vital signs including heart rate, blood oxygen level, and blood pressure by the healthcare team. The neurosurgeon will then remove a portion of your skull, potentially conducting an EEG to confirm seizure origins, and in certain instances, you may be temporarily awakened to respond to the surgeon’s queries, aiding in brain mapping without pain sensation. Following this, you’ll be returned to unconsciousness, and the neurosurgeon will address the seizure-affected brain tissue using the appropriate surgical method, before replacing and securing the skull bone and closing the incision with bandaging. The entire epilepsy surgery typically spans several hours.

After the procedure

Following epilepsy surgery, anticipate scalp and facial swelling as well as headaches, managed with medications that alleviate these symptoms, typically resolving within a few weeks. Most individuals require one day of intensive care followed by a hospital stay lasting three to four days. Anti-seizure medications will continue post-surgery to safeguard brain healing and reduce seizure risks. Rest is crucial as you gradually resume normal activities over four to six weeks, with a return to work or school expected within one to three months. If seizure-free for a year or longer, medication dosage may be gradually reduced or stopped by your healthcare provider. Rehabilitation therapy is unnecessary unless vital functions such as speech, memory, or movement are impacted.

Outcome

The success of your epilepsy surgery hinges on various factors, including the type, frequency, and severity of your seizures, the specific brain region involved, the chosen surgical procedure, your age, and any pre-existing health conditions you may have.
In about half of cases, individuals undergoing an epilepsy surgical assessment may require the insertion of small electrode wires into their brain for further testing to pinpoint the seizure source.

For those opting for neuromodulation surgeries, approximately half may experience improved seizure control. In contrast, between 50% and 85% of individuals undergoing resection surgery or hemispherectomy may observe significant enhancements in seizure management, with some even achieving seizure freedom.

To gain clarity on the potential outcomes specific to your situation, it’s essential to discuss these factors with your neurosurgeon.