Epilepsy is a neurological condition characterized by recurrent, unprovoked seizures, which are sudden bursts of abnormal electrical activity in the brain. For many individuals, daily medications effectively manage these seizures. However, when seizures persist despite treatment, a more advanced diagnostic approach may become necessary. Stereoelectroencephalography, commonly known as SEEG, is a sophisticated medical procedure designed to precisely identify the brain regions responsible for generating these difficult-to-control seizures. This minimally invasive technique offers a detailed view of brain activity, guiding subsequent treatment decisions.
The Purpose and Candidacy for SEEG
SEEG serves a specific purpose in epilepsy care, primarily for individuals diagnosed with drug-resistant, or refractory, epilepsy. This diagnosis applies when at least two different antiseizure medications have failed to adequately control seizures. In these situations, non-invasive tests, such as standard scalp electroencephalograms (EEGs) and magnetic resonance imaging (MRIs), may not pinpoint the exact location where seizures begin. The primary goal of SEEG is to precisely identify this seizure onset zone, also known as the epileptogenic zone, to determine if a patient might benefit from surgical intervention.
SEEG allows medical teams to explore deeper brain structures and both hemispheres of the brain, areas inaccessible with conventional scalp EEGs or older invasive techniques like subdural grids. Both adults and children, typically those over two years of age, who meet the criteria for drug-resistant epilepsy and have unclear non-invasive test results, may be considered candidates for this diagnostic procedure.
The Implantation and Monitoring Process
The SEEG procedure begins with meticulous pre-surgical planning, where neurosurgeons utilize advanced imaging techniques like MRI and computed tomography (CT) scans. These scans generate a detailed three-dimensional map of the patient’s brain. This map allows the surgical team to precisely plan the trajectories for inserting the electrodes, carefully navigating around blood vessels and other sensitive anatomical structures to ensure safety and accuracy.
The surgical implantation itself is a minimally invasive procedure performed under general anesthesia. Surgeons create several tiny incisions in the scalp and drill small holes, just large enough to pass thin, flexible electrodes into the brain. These electrodes are then carefully guided to the predetermined deep brain targets. Many institutions utilize robotic assistance, such as the ROSA® system, to enhance the precision and efficiency of electrode placement, with 10 to 15 electrodes implanted during the procedure.
Following the implantation, patients are transferred to a specialized Epilepsy Monitoring Unit (EMU) for an in-hospital monitoring phase. Here, the implanted electrodes are connected to equipment that continuously records the brain’s electrical activity, often alongside video monitoring. The main objective during this period is to safely capture the patient’s typical seizures while under constant observation. In some cases, medication dosages may be carefully adjusted to facilitate the occurrence of seizures for recording purposes.
Analyzing SEEG Data to Map Seizures
Once the monitoring period concludes and sufficient seizure activity has been recorded, a specialized medical team, including epileptologists and neurophysiologists, meticulously analyzes the extensive electrical data. This analysis involves interpreting the complex brain signals captured by each electrode. The goal is to create a precise, three-dimensional map that illustrates exactly where seizures originate within the brain and how their electrical activity propagates through different brain regions.
Advanced computational methods are employed to model seizure activity as a network graph, which helps characterize the spatial and temporal progression of these events. This detailed mapping helps distinguish the seizure onset zone from other brain areas. In some instances, electrical stimulation is also performed through the implanted electrodes during monitoring. This stimulation can help identify areas of the brain responsible for functions like language or movement, and may also be used to provoke the patient’s typical seizures, providing additional insights into the seizure network.
Therapeutic Interventions Following SEEG
The precise seizure map generated from SEEG data forms the foundation for determining the most appropriate therapeutic intervention. If the SEEG evaluation identifies a single, well-defined seizure focus located in a part of the brain that can be safely accessed, resective surgery may be recommended. This involves the surgical removal of that small piece of brain tissue, offering the highest chance for seizure freedom.
Another less invasive option is Laser Interstitial Thermal Therapy (LITT). In this procedure, a thin laser fiber is guided to the seizure focus, and heat energy is used to precisely destroy the problematic brain tissue. SEEG-guided radiofrequency ablation (RFA) is a similar technique that can be performed through the electrodes to destroy seizure-generating cells.
If the seizure focus is in an area that cannot be safely removed without risking neurological deficits, or if seizures originate from multiple brain regions, neuromodulation therapies may be considered. Responsive Neurostimulation (RNS) involves implanting a device that continuously monitors brain activity and delivers targeted electrical stimulation when it detects abnormal seizure patterns. Deep Brain Stimulation (DBS) is another neuromodulatory approach, where electrodes are placed in specific brain areas to modulate brain activity and reduce seizure frequency.