Epilepsy surgery has benefited from an explosion of technological innovations that have broadened the horizons of who can be treated and the extent to which their disease can be managed. Literature reports if a patient continues to have seizures despite having tried two anti-seizure medications, the chances of the next medication controlling seizures is less than 5%. These patients are then diagnosed with intractable epilepsy and should be evaluated by an epileptologist for epilepsy surgery consideration. Epilepsy surgery is the process where the epileptogenic zone of the brain is resected in hopes of halting seizures and potentially curing patients of their epilepsy. Before this happens, there are several stages preceding the surgery itself, often referred to as the presurgical evaluation.
The presurgical evaluation involves several steps, the first of which involves admission to the Epilepsy Monitoring Unit where the medical team monitors the patient’s EEG activity to record seizures and localizes the epileptogenic zone. This EEG data can then be processed through source localization that involves neuroimaging techniques and complex mathematical analysis to further assess where the seizure focus is. MEG (magnetoencephalography) measures small magnetic fields produced by electrical currents in the brain in combination with magnetic source imaging to identify the seizure focus. Other techniques that may be used in conjunction with the aforementioned studies include a PET (Positron Emission Topography) scan to assesses how the brain uses energy, co-registering it with the MRI (magnetic resonance imaging) to determine if there are any overlaps in areas that are abnormal. In some patients, a SPECT (Single-Photon Emission Computed Tomography) scan can assess if there are areas of abnormal blood flow in the brain to localize where the seizure focus is arising from. Taken altogether, this data helps the patient’s epilepsy team hypothesize where the epileptogenic zone is to guide the medical team’s next steps, which often include intracranial electroencephalography monitoring.
Intracranial electroencephalography monitoring involves placing electrodes, referred to as grids and strips, directly on the patient’s brain via a craniotomy or using stereoelectroencephalography (sEEG) to identify where the seizures are arising from. sEEG involves using a Talairach frame to place these electrodes and can take several hours in the operation room, translating to prolonged time under anesthesia. Over the past decade or so, the invention of ROSA™ (Robotic Stereotactic Assistance) system has opened the door to the world of minimally invasive epilepsy surgery. This system employs a robotic arm together with MRI neuroimaging to place these sEEGelectrodes more precisely and in a fraction of the time compared to previous techniques using the Talairach frame. This leads to shorter OR time, less anesthesia exposure, and patients often recover faster shortly after leaving the OR. Once seizures are captured and analyzed, the team will study the intracranial monitoring results to guide the next steps of care.
Patients often worry about any potential neurological deficits following surgery, which is largely determined by the extent of the resection: the larger the resection, the more potential for post-surgical complications and/or deficits. The goal is to minimize the resection volume as much as possible while including the entire epileptogenic zone. If the epilepsy focus is deep, the required access to resect this region can be technically and surgically challenging. However, if the area is confined to a specific region, LITT (Laser Interstitial Thermal Therapy) treatment may be a viable option. This technique involves a small incision coupled with the ROSA™ robotic arm to deliver carefully monitored pulses of heat to “burn” and obliterate the epileptogenic zone while protecting the surrounding healthy tissues.
This minimally invasive approach provides for a faster recovery time and shorter hospital stay.
Another recent technological advance is RNS (Responsive Neurostimulation) technology that allows certain patients to become the surgical candidate who was previously deemed, non-surgical candidates. As previously discussed, there may be neurological deficits following surgery, especially if the epileptogenic zone includes eloquent cortex where resection of these regions will cause undesirable functional outcomes.
Other patients may have multiple brain areas that are causing seizures, making resection of all these regions a challenge.
With the availability of RNS, these patients now have a surgical option that can be curative and not suffer any neurological deficits. Briefly explained, the epileptogenic zones are covered by implanted EEG electrodes and connected to a small EEG detection device implanted in the skull. This device continuously monitors EEG activity and can be programmed to detect EEG seizure activity at which time, it will deliver an electrical impulse to stop the seizure. As the device continues to learn the patient’s seizure pattern, the detection becomes more precise over time.
In patients where the epileptogenic zone is too broad for surgical resection, other treatment options include VNS (Vagal Nerve Stimulation) where a neurostimulator is implanted in the chest and connected to the vagus nerve in the neck. Another recently approved medical device, DBS (Deep Brain Stimulation), involves placing electrodes in the anterior thalamus (deep part of the brain) and connected to a neurostimulator in the chest. In both devices, electrical stimulation is sent directly to the brain to reduce seizure frequency and severity.
Epilepsy is one of the most common neurological problems, and up to 20-40% of patients with epilepsy can become refractory to conventional medications. Seizures negatively impact these patient’s lives in several aspects from cognitive skills to mental health, employment, relationships, and social interactions.
Hence the goal of treatment is to eliminate them and if this is not possible, minimize the seizure burden to afford patients optimal quality of life. Innovative technology has propelled epilepsy treatment into new frontiers, allowing more people to live seizure-free and have a greater degree of control over this debilitating disease.