10 Stereo-EEG (SEEG)
10.1 What is stereo-EEG?
If your child has seizures that medications have not been able to control, your epilepsy team may recommend a test called stereoelectroencephalography, usually shortened to SEEG or stereo-EEG. SEEG is a surgical procedure that places thin wire electrodes inside the brain to record electrical activity from areas suspected to be involved in your child’s seizures. The goal is to identify the seizure onset zone, the area or network of areas where seizures most likely begin1.
You may already be familiar with regular EEG, where electrodes are glued to the scalp. Scalp EEG is a good starting point, but it is best at detecting electrical activity that reaches the surface of the brain. Seizures that begin deep inside the brain, or in areas where signals are distorted by surrounding tissue, can be difficult to detect clearly on a scalp recording. SEEG solves this by placing electrodes inside the brain itself, which lets the team record from areas a scalp EEG simply cannot reach as clearly2.
Doctors sometimes use an analogy that captures why this step matters. Scalp EEG and MRI can usually tell the team the general neighborhood where seizures are coming from, something like a zip code. SEEG helps narrow that down much further, toward the street and sometimes the house. It rarely points to a single house with total certainty, though, because epilepsy often involves a network of connected brain areas rather than one isolated spot3.
10.2 Why do we do it?
Not every child needs SEEG. Your epilepsy team will only recommend it after other tests, including scalp EEG and MRI, have narrowed things down but have not given a clear enough answer to plan surgery safely2. This usually happens in one of a few situations: when MRI does not show a clear abnormality despite evidence that seizures are coming from one area, when there seem to be multiple possible starting points, or when the suspected area sits close to parts of the brain that control movement, sensation, or language, and the team needs to know exactly how close.
The goal of SEEG is to answer two questions at once. First, does the information suggest that treating a particular area is likely to improve seizures? Second, can that be done safely, without causing new problems? Getting clearer answers to both questions is what allows the team to recommend the treatment option most likely to help, whether that is surgery to remove the seizure focus, a laser procedure, or a device such as a responsive neurostimulator2. SEEG is typically reserved for the roughly one in five children with drug-resistant focal epilepsy in whom non-invasive testing alone is not enough to determine whether surgery is an option1.
SEEG is a diagnostic test, not a treatment on its own. Its purpose is to gather information. What happens afterward, whether that is surgery, a different procedure, or a change in medical management, depends on what the recording shows.
10.3 How is SEEG done?
SEEG is placed under general anesthesia, so your child will be fully asleep and will not feel the procedure. The surgical team uses images from your child’s MRI and CT scans, combined with everything learned from prior testing, to decide exactly where the electrodes need to go4. Many centres now use a surgical robot to help place the electrodes with a high degree of precision, which can shorten the time your child spends in the operating room3.
The surgery itself usually takes a few hours. The team creates several small twist-drill openings in the skull, each only a few millimeters wide, and carefully passes a thin, semi-rigid electrode through each one into the planned area of the brain2. The electrodes need to be somewhat stiff, rather than flexible, so they follow a precise, planned path into the brain. Many children have around a dozen or more electrodes placed, depending on how many brain regions need to be studied3. Afterward, your child’s head is wrapped in a bandage, and you will not be able to see the electrodes or the small bolts that hold them in place.
After surgery, your child moves to the epilepsy monitoring unit, the same type of unit used for a regular EEG stay. The electrodes usually stay in place for about 5 to 14 days, while the team waits for seizures to happen and records them in detail2. During this time, your child’s seizure medications are often reduced to help seizures occur sooner. The team may also do brief testing called brain mapping, where a small current is passed through some electrodes to check what function that part of the brain controls, such as speech or movement. This can briefly produce sensations, small movements, or other experiences, and your child’s team will explain what to expect before it happens3.
Once the team has recorded enough seizures, the electrodes are removed in a short procedure, usually done under sedation or anesthesia depending on your child’s age and the centre’s usual practice, and your child goes home a day or two later2.
10.4 Benefits of SEEG
Compared with older approaches that required a larger opening in the skull to place electrode grids directly on the surface of the brain, SEEG is less invasive. Children who undergo SEEG tend to have shorter surgeries, shorter hospital stays, and less pain afterward, because there is no need to remove a section of skull. Studies comparing the two approaches directly have found SEEG carries a lower rate of complications and shorter operating room times than surface grids, with similar chances of a successful outcome5,6. SEEG can also reach deep brain structures and both sides of the brain at once, which surface electrodes cannot do, giving the team a more complete picture of where seizures start and how they spread2.
Perhaps most importantly, SEEG lets the team combine two goals that used to be harder to achieve together: finding the seizure focus precisely, and mapping the surrounding functional brain areas that must be protected. Doing both at once helps your child’s team plan a treatment that is both effective and as safe as possible for the areas that control everyday abilities4.
10.5 Risks of SEEG
SEEG is considered a safe procedure. Serious complications such as bleeding in the brain or infection occur in roughly 1 to 4 percent of cases, depending on the study, and are generally less common than with the older surface grid approach1,7. Still, this is brain surgery, and every family should understand that any surgery carries some risk, including bleeding, infection, and rarely stroke2.
Some children have mild headaches, scalp tenderness, or jaw discomfort while the electrodes are in place, since some electrodes pass near the jaw muscles. Your child’s team will manage this with pain medication as needed. There is also a chance, even after all this effort, that the recording does not clearly localize where seizures start. This does not mean the test failed. It means the team has learned something important: that the seizure network may be broader or more complex than first thought, which itself shapes what comes next.
10.6 What happens with the results?
Once monitoring is complete, your child’s case is reviewed by the full epilepsy team, including neurologists, neurosurgeons, and neuroradiologists, at a patient management conference4. The team looks at where seizures started, how they spread, and what the mapping showed about nearby function. From there, they will discuss options with you. These may include surgery to remove the area causing seizures, a minimally invasive laser procedure, or a neuromodulation device such as responsive neurostimulation, deep brain stimulation, or vagus nerve stimulation, if the seizure focus involves an area that cannot be safely removed. Which of these options is available and appropriate depends on your child’s age, epilepsy type, and other individual factors, so your team will walk you through what applies to your child specifically3.
If surgery is recommended, it usually happens about four to eight weeks after SEEG, giving your child time to recover first2.
10.7 SEEG does not diagnose epilepsy by itself
It is worth being clear about what SEEG is, and is not, for. SEEG is not used to prove whether your child has epilepsy. By the time SEEG is being considered, the diagnosis of epilepsy is usually already clear from prior history, scalp EEG, and imaging. Instead, SEEG answers a more specific question: where in the brain are seizures starting or involving, and how might that be treated safely. Keeping this distinction in mind can help make sense of the results, even when they are more complicated than a simple yes or no.
10.8 Why getting it right is so hard
It helps to understand why SEEG, for all its precision, is one of the most difficult tests in epilepsy care to plan and interpret well.
Unlike an MRI or a blood test, SEEG only records from the specific spots where electrodes are placed. Before the surgery even happens, your child’s team has to form a hypothesis, essentially an educated guess, about where the seizures are most likely coming from, based on scalp EEG, MRI, and other tests such as PET or MEG when available. The electrodes are then placed to test that hypothesis. This means SEEG can only find what it is looking for. If the true seizure focus lies outside the areas that were sampled, even a technically perfect recording may miss it8.
This is often called a sampling problem, and it is the central challenge of SEEG. The brain contains billions of neurons organized into complex, connected networks, and even a dozen or more electrodes only sample a small portion of that network. Choosing where to place them requires weighing every piece of prior information carefully, because each electrode represents a decision to look somewhere, and by necessity, a decision not to look somewhere else.
Seizures themselves add another layer of difficulty. The first electrode to show seizure activity is not always located at the true seizure onset zone. Seizures can start in an area with no electrodes nearby, spread quickly to a region that does have electrodes, and appear on the recording as if they started there. Experienced epileptologists spend years learning to recognize the subtle timing and pattern differences that separate a true seizure onset from an area of early spread.
There is also the matter of how many seizures are enough. Capturing one seizure is rarely sufficient, since a single event may not represent a child’s typical seizure pattern. Teams generally want to see several seizures, ideally ones that look like the child’s usual seizures at home, before feeling confident in the result. Research on children who underwent SEEG has found that capturing four or more seizures meaningfully increases the chance of clearly identifying the seizure onset zone9. This is part of why SEEG monitoring can take a week or longer, and why, on rare occasions, the stay is extended if seizures are not happening on their own schedule.
Even with careful planning, SEEG does not always find a clear, single answer. In published series, a clear seizure onset zone is identified in the large majority of children studied, but not all, and even when one is found, not every child goes on to have surgery, since sometimes the area involved turns out to be too widespread, too close to essential brain function, or otherwise not safe or likely enough to help to remove9,10. This is not a failure of the test. It is a reflection of how varied and, in some cases, how complex the underlying epilepsy can be.
Finally, every brain is organized somewhat differently, and epilepsy itself can reorganize how nearby brain areas function over time, especially in children whose brains are still developing. This means findings from one patient cannot simply be applied to the next. Each SEEG plan has to be built individually, combining imaging, prior EEG, seizure descriptions, and sometimes newer tools like connectivity analysis, and even then, the team is working with an incomplete map of a complex system that can behave differently from one child to another11.
If your child’s SEEG results are less clear than hoped, this is a known and understood limitation of the test itself, not a sign that something went wrong. Your epilepsy team will talk through what was learned and what the next reasonable step looks like, whether that means more testing, a period of watchful waiting, or reconsidering surgical options.
10.9 Key takeaways
SEEG is a safe, minimally invasive way to record seizure activity from inside the brain when scalp EEG and MRI are not enough to plan surgery on their own. Rather than pinpointing a single spot with certainty, it helps the team map the network of brain areas involved in your child’s seizures and identify the most likely place to intervene. It takes real skill and careful teamwork to plan where electrodes go, interpret what they record, and turn that information into a treatment plan that gives your child the best chance at fewer seizures and a better quality of life.