Overview of Epilepsy Surgery
Epilepsy surgery is considered as a possible treatment for 30% to 40% of patients who continue to experience seizures even after they have been on medication for one year with a sufficient dose of two anti-seizure drugs. Despite the fact that removing part of the temporal lobe (the front part of the brain) has been a classic surgical procedure to treat epilepsy, there’s been a change in how this surgery is approached.
Currently, the focus is on making sure as many of the neural pathways (networks in the brain through which information travels) causing the seizures are disconnected as much as possible. This is quite a contrast to the old idea of trying to remove as much of the problematic brain area as possible.
Anatomy and Physiology of Epilepsy Surgery
For epilepsy surgery to work as well as possible, doctors need to perform certain steps that interrupt the brain networks that cause seizure-like symptoms. These steps include:
1. Cutting out a part of the cortico-thalamic tract, which is a pathway in the brain that helps control various bodily functions.
2. Removing sections of the medial temporal structures, which are parts of the brain involved in long-term memory and emotion.
3. Conducting a total corpus callosotomy, which involves severing the large band of nerve fibers connecting the two hemispheres of the brain to limit the spread of seizures.
4. Disconnecting the orbito-fronto-hypothalamic tract, which is a part of the brain that helps regulate various functions like hunger, thirst, and body temperature.
Why do People Need Epilepsy Surgery
If someone has epilepsy that isn’t getting better with medicine, they might need surgery. This idea is widely accepted by epilepsy experts around the world, as stated by the International League Against Epilepsy (Epilepsy is a brain disorder that causes repeated, uncontrolled electrical activity resulting in seizures).
When doctors examine tissue samples from people who’ve had epilepsy surgery, they often find changes in the brain. Adults usually show signs of damage in the hippocampus – an area of brain linked with memory and learning, while children often have an abnormal formation or development of the cerebral cortex, the outermost layer of our brain.
In specific cases, a type of surgery called a hemispherectomy might be needed. This operation involves the removal of one side of the brain. Some conditions might absolutely require this surgery, including Sturge-Weber syndrome (a rare disorder present at birth marked by distinctive discoloration of the skin and risk of glaucoma), cortical dysplasia (abnormal brain development), hemimegalencephaly (oversized brain half), Rasmussen Syndrome (progressive nervous system disorder), porencephaly (a cyst or cavity in the brain), and hemiconvulsion-hemiplegia-epilepsy syndrome (a severe form of epilepsy with other complications).
In cases where the areas causing seizures can be identified and safely removed, a different kind of surgery called a resective procedure would be performed.
Epilepsy surgery is also recommended in patients where the seizures show specific symptoms indicating their origin in the brain.
The type of epilepsy surgery used depends on a variety of factors, including what’s causing the seizures, how the seizures express themselves, and the personal factors related to the patient’s condition.
When a Person Should Avoid Epilepsy Surgery
There are certain situations where surgery to treat epilepsy may not be advised. These include:
1. If the patient is dealing with a serious psychiatric illness that’s currently affecting them. It could make the surgery more complicated or risky.
2. Severe other medical conditions that make surgery unsafe or unwise. In simpler words, if the patient’s other health problems could make surgery dangerous.
3. If doctors can’t locate the specific area in the brain (called the epileptic foci) where the seizures are starting. This might make surgery less successful, unless the patient is having frequent episodes of suddenly losing muscle control and falling down (known as drop attacks). In these cases, a special type of surgery called a corpus callosotomy may still be suggested.
Equipment used for Epilepsy Surgery
When a patient is being assessed, several steps are usually followed:[4]
1. High-quality imaging using a technique known as magnetic resonance imaging (MRI) is performed. This procedure helps visualize the brain in detail. Some of the specific techniques used in this procedure include short tau inversion recovery (STIR), fluid-attenuated inversion recovery (FLAIR), and susceptibility-weighted imaging (SWI). These help to highlight different aspects of the brain’s structure and function.
2. Video scalp electroencephalography (EEG) is done. This test involves attaching small sensors to the scalp to record electrical activity in the brain. It helps to detect abnormal electrical brain patterns that can cause seizures.
3. A thorough mental and psychological assessment is also done. These tests give insight into the patient’s memory, attention, and other cognitive abilities.
If it’s hard to pinpoint the area in the brain where seizures are starting from, more detailed investigations might be needed:
1. Diffusion tensor imaging, a special kind of MRI, is used for studying the brain’s wiring and how different parts connect and communicate.
2. Interictal high-resolution EEG, magnetoencephalography (MEG) and functional MRI (fMRI) are applied. These techniques can help identify the seizure originations in the brain.
3. A scanning technique called positron emission tomography (PET) may be used, it can show areas of lowered metabolism in the brain, which could signal areas that cause seizures.
After the operation, the following procedures may be used to assess any potential deficits in brain function:
1. Functional MRI, MEG, and the Wada test, which are used to identify areas of the brain controlling language and memory.
2. Tractography of the Meyer loop and visual field testing – they help in assessing any vision problems.
3. Functional MRI and tractography of the pyramidal tract, used to check for any movement-related deficits.
Preparing for Epilepsy Surgery
Treating seizures often involves a three-step process, which requires teamwork between different healthcare professionals. Here is a simplified breakdown of what each phase entails:
Phase 1: During this phase, understanding the specific characteristics of your seizures is critical. This includes neurophysiology testing or studying the brain’s electrical activity, an MRI (a type of scan that shows detailed images of the brain) specifically designed to detect seizures, functional neuroimaging (which observes how different parts of the brain work during a seizure), and neuropsychological testing (this assesses your brain’s performance).
Phase 2: If the medical team agrees that the details of your seizures, imaging studies, and neurophysiological tests all point to the same conclusion, the next step involves the use of an intracranial EEG. An EEG (Electroencephalography) is a test used to detect electrical activity in your brain – intracranial means it’s placed directly on the brain.
Phase 3: The final step is a specialized surgery, tailored to your specific needs. This might involve removing (resective surgery) or disconnecting (disconnection surgery) the part of your brain causing the seizures.
These steps are designed to systematically understand and treat seizures more effectively based on your unique situation.
How is Epilepsy Surgery performed
Resective surgery is a type of procedure aimed at removing parts of the brain that cause seizures in patients. Recent developments in medical technology have given way to minimally invasive techniques such as stereotactic radiosurgery, MR-guided laser interstitial thermal therapy (MgLiTT, a way to target and eliminate small areas of the brain), and SEEG-guided radiofrequency thermal coagulation (a method that uses heat to destroy abnormal brain tissue).
For patients with non-lesional epilepsy disorder, a condition where no obvious cause for epilepsy can be spotted in the brain, surgeries have shifted from major operations like hemispherectomy (removing one side of the brain) to less invasive methods such as disconnection procedures, like hemispherotomy (a type of surgery that disconnects one half of the brain from the other).
In some cases, where surgery isn’t an option, seizures can still be reduced using techniques like vagal nerve stimulation (introducing mild electrical pulses to the brain via the vagus nerve) and deep brain stimulation (sending electrical impulses to certain parts of the brain).
One specific surgical procedure, called Peri-Insular Hemispherotomy, involves several steps including:
1. Blocking off certain parts of the brain, such as the suprasylvian block and the infrasylvian block, which involves removing parts of the frontal and temporal neocortex;
2. Cutting across the corona radiata, a white matter sheet that lies between the cerebral cortex and the brain stem;
3. Removing part of the temporal lobe;
4. Dividing the corpus callosum, the part of the brain that allows communication between the two hemispheres;
5. Disconnecting the frontoparietal region (the upper front part of the brain);
6. Finally, resecting the insula, which involves removing a part of the insular cortex, a region in the brain thought to play a role in consciousness and emotions.
The patient is placed on their back with their head turned to the side opposite to the one being operated on. The surgeon then makes an opening in the skull and begins the above steps to disconnect the brain regions involved in seizures.
There are other similar procedures too, like the Anterior Temporal Lobectomy and Amygdalohippocampectomy, which involve removing the temporal lobe and other structures deep within the brain associated with emotions and memory respectively.
Selective Amygdalohippocampectomy aims to preserve as much of the brain as possible and uses either a subtemporal, transcortical, or trans-Sylvian approaches.
Types of surgical management for seizures originating within the important areas of the brain include Multiple Subpial Transections. This procedure involves making a series of small cuts perpendicular to the folds in the brain, which helps to disrupt the intercortical neural connections while preserving the subcortical fibers.
Vagal Nerve Stimulation offers up to a 50% reduction in seizure frequency for patients who are considered high-risk for major surgical procedures. This involves placing electrodes on the left side of the vagus nerve, 8 cm above the collarbone, with boosts of stimulation from a small device placed under the skin in the chest. The major seizure control role is predominantly governed by the lower branch of the vagus nerve.
Possible Complications of Epilepsy Surgery
Epilepsy surgery might have some complications. Here’s a list of them:
1. Superficial hemosiderosis: This is a buildup of iron in the blood from bleeding in the brain. This can happen after a type of surgery called an anatomic hemispherectomy.
2. Progressive hydrocephalus: This is a condition where fluid builds up in the brain, causing pressure. It can also happen after an anatomic hemispherectomy.
3. Postoperative infarction: This is damage to tissue because it isn’t getting enough blood. It can happen if there’s an injury to a particular vein, called the Sylvian vein, during surgery.
4. Sinus thrombosis: This is a blood clot in the sinuses, which can be a risk after any surgery.
5. Memory decline and anomic aphasia: These can affect memory and speech. These can happen after surgery on a part of the brain called the temporal lobe.
6. Vasospasm and contralateral superior quadrantanopia: These are conditions that can cause vision problems. They can happen after a surgery called an amygdalohippocampectomy, if a part of the brain called Meyer’s loop is injured.
7. Disconnection syndrome: This is a group of symptoms that can happen after a surgery called a corpus callosotomy, where the two sides of the brain are separated.
8. Hemiparesis and dysphagia: These can cause weakness on one side of the body and trouble swallowing. They can happen after a surgery called multiple subpial transections.
9. Cough and hoarseness of voice: These symptoms can happen after a surgery called vagal nerve stimulation, which affects a nerve that runs from your brain to your stomach.
What Else Should I Know About Epilepsy Surgery?
Epilepsy surgery is performed to stop or reduce seizures. Yet, this goal is achieved in only up to 80% of cases. Some factors have been identified that might contribute to continuing seizures after surgery. These factors include abnormal brain activity in certain regions, and not completely removing a specific part of the brain called the uncinate fasciculus.
Scientists use a special type of brain imaging called diffusion tensor imaging to identify any remaining connections in the brain that could be causing seizures. Another factor influencing whether a patient might become seizure-free is whether the area of brain tissue removed in surgery is the actual source of the seizures.
Outcomes aren’t as good for patients whose seizures originate outside of the brain’s temporal region, or whose seizures start in a difficult-to-define area. If seizures come back within two years after surgery, it’s also not a good sign. If seizures spread quickly because of abnormal nerve activity outside the area removed during surgery, it can significantly lead to seizures coming back after surgery.
