Invasive electroencephalography (EEG) monitoring before epilepsy surgery

Invasive EEG monitoring is a test to pinpoint where seizures start in the brain. It is also called invasive subdural grid/depth and strip epilepsy mapping.

The test involves using a grid of electrodes placed directly on your child’s brain to monitor your child’s brain activity so doctors can find and record the onset of your child’s typical seizures.

Your child will need brain surgery to place the electrodes and will be monitored over three to five days.

Invasive electroencephalography (EEG) monitoring

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.

Does invasive EEG monitoring have any risks or side effects?

There are typically no risks or side effects from invasive EEG monitoring.

What happens before my child’s surgery?

Once your child is scheduled for invasive EEG monitoring, you will meet your child’s neurosurgeon (who will perform the surgery), the epilepsy neurologist (who will review the EEG data) and epilepsy 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 also give you a date and time to come to the hospital for your child’s surgery and explain how to prepare your child.

Different types of invasive  electrodes

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.

What happens when my child arrives for invasive EEG monitoring?

When you arrive at the neurosurgery unit, a nurse and an anaesthesiologist will assess your child and prepare them for surgery.

Once this is done, they will take your child to the operating room. There, the anaesthesiologist will give your child sleep medicine. Once your child is asleep, the neurosurgeon will expose your child’s brain and place the special grid of embedded electrodes on the brain’s surface. Sometimes the surgeon will also place depth electrodes to monitor deeper parts of the brain.

When all the electrodes are placed, they will be tested to see if they are working and your child's scalp will then be stitched closed. Your child’s head will then be bandaged and your child will be taken to the critical care unit for recovery and the start of invasive EEG monitoring.

What happens during invasive EEG monitoring?

Your child will be in bed for three to five days while invasive EEG monitoring takes place. The electrodes placed on their brain will be connected to a video EEG machine that will continuously record their brain’s electrical activity and capture any seizures on video.

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.

• If the source of seizures in your child’s brain is identified, your child will have surgery the next day to remove the electrodes and remove the area of the brain that is causing their seizures.
• If doctors cannot find the source of your child’s seizures, they will try again over the following few days. If they still cannot find the source, your child will then go to the operating room to have the electrodes removed. As it will not be possible to remove the source of the seizures you and your child’s healthcare team will use the information from invasive EEG monitoring to discuss other treatment options.

At SickKids

If you have any questions about the test, please contact your child’s neurologist.​