Invasive EEG monitoring is a test to pinpoint where seizures start in the brain. This is done by a technique called stereo-EEG (SEEG).
SEEG is an advanced diagnostic method used in children with epilepsy who are being evaluated for surgical management.
SEEG helps health-care providers to more precisely localize the foci of seizure generation as EEG signals are directly picked up from the brain areas, both superficial and deep. This helps with better surgical planning, resulting in better seizure freedom and minimal neurological deficits.
Why does my child need invasive EEG monitoring?
Invasive EEG monitoring is needed if:
- the source of your child’s seizures cannot be found with a scalp EEG or other standard brain monitoring tests
- seizures occur in parts of the brain that are close to important functional areas, such as areas related to speech and hearing
What are the benefits of SEEG?
- Minimally invasive neurosurgical technique; does not involve a craniotomy (opening of the skull).
- Better tolerated by children: less pain, early recovery, more mobile during the recording period.
- Rare occurrence of serious neurosurgical complications as compared to the older techniques where grid electrodes were placed on the surface of the brain.
- Evaluation of EEG from wider brain regions, deep foci and both halves of the brain.
- More precise localization of seizure foci in selected patients.
Is it safe in young children?
SEEG is well tolerated in young children, with very rare complications. However, a child needs adequate skull thickness to be able to hold the SEEG wires (electrodes) in place for long recording periods. The target skull thickness is achieved by two to three years of age, at which point SEEG can be safely performed.
Does SEEG monitoring have any risks or side effects?
SEEG is a relatively well tolerated neurosurgical procedure with minimal complication rates. Complications may include incorrectly placed electrodes, infection, small blood collection or cerebral spinal fluid (CSF) leaks. Strict surveillance is maintained in the post-operative period by the epilepsy team.
What happens before my child’s surgery?
Once your child is scheduled for SEEG), you will meet your child’s neurosurgeon (who will perform the surgery), the epilepsy neurologist (who will review the EEG data) and epilepsy nurse practitioner or nurse.
This team will explain the goals of the surgery to place the electrodes and what to expect before, during and after invasive EEG monitoring. They will give you a date and time to come to the hospital for your child’s surgery and explain how to prepare your child. You will also be given an anti-seizure medication wean plan, if needed, to start before the surgery, as the purpose of the procedure is to study your child’s seizures.
How do I prepare my child for invasive EEG monitoring?
- Explain what will happen during invasive EEG monitoring in words your child understands.
- Make sure your child stops eating and drinking from midnight the night before surgery. If these instructions are not followed, the surgery will be cancelled.
- There is no need to shave your child’s head or remove their hair before the surgery.
What happens when my child arrives for invasive EEG monitoring?
When you arrive at the neurosurgery unit, a nurse and an anesthesiologist will assess your child and prepare them for surgery.
Once this is done, they will take your child to the operating room. There, the anesthesiologist will give your child a general anesthetic to put them to sleep. Once your child is asleep, the neurosurgeon will start the surgery.
During the surgery, tiny holes are made in the scalp/skull and thin (0.8 to 1.2 mm diameter) wires (also called electrodes) are then inserted accurately into the finalized targets under image guidance. The number of electrodes implanted varies with each child. The procedure may last between four to six hours.
After the procedure, a brain MRI is repeated to confirm the position of the inserted electrodes. Following this, your child may be shifted to the intensive care unit (ICU) briefly for observation. Once stable, your child is then moved to the epilepsy monitoring unit.
Electrical activity from the electrodes is then recorded as EEG and studied by the epilepsy team. The team will try to localize the most probable focus that is generating seizures. Based on these results, further definitive surgery (like resection of the seizure focus) may be planned.
Parents/caregivers are updated on a regular basis and when some results are ready to be discussed.
What happens during SEEG monitoring?
The health-care team usually waits to record two to three typical seizures of the child during the SEEG monitoring. For most children, this happens within one week. However, it is difficult to predict the occurrence of seizures in epilepsy. For some children, the SEEG electrodes may need to be kept longer if seizures do not occur within the first week. These electrodes may be kept for a maximum of two to three weeks. This is done to minimize the risk of infection with longer periods. .
What should I expect after invasive EEG monitoring?
Once all the EEG seizure data has been captured and analyzed, you will meet with the epilepsy surgery monitoring team to discuss the results.
Once the epilepsy team is satisfied with the EEG data obtained, the SEEG electrodes are removed. The removal of electrodes is done under local anesthesia and may take 15 to 30 minutes.
After this, there may be three scenarios:
- The epilepsy team is very sure about the seizure focus and recommends the resection or laser ablation (“burning”) of the focus right away after removal of electrodes.
- Sometimes, EEG data obtained requires more detailed analysis. In this case, the epilepsy team may recommend more definitive surgery after a waiting period (e.g., one to two months).
- EEG data obtained may suggest more extensive brain involvement (e.g., multiple foci of seizures or seizures coming from both halves of the brain). As a result, the epilepsy team may not recommend any further surgery. They may suggest alternative plans to control the seizures.
At SickKids
If you have any questions about the test, please contact your child’s neurologist.