Invasive monitoring for epilepsy

Invasive monitoring is another way of confirming the area of the brain from which seizures (fits) associated with epilepsy originate.

How it works

Invasive monitoring involves an operation at Great Ormond Street Hospital (GOSH) to place electrodes, in strips or grids, directly over the surface of your brain. These electrodes are then connected to an EEG (electroencephalogram) machine so that technicians can record your brain activity over several days.

Why you might need this test

The procedure will be carried out if doctors think that your epilepsy might be relieved by an operation to remove the part of your brain which is causing the problem. Previous tests will have already given the team some idea which area of your brain needs closer observation. This test will confirm which area of your brain is causing seizures.

Invasive monitoring can also allow the Epilepsy team to carry out 'functional brain mapping'. This mapping allows the team to check exactly which areas of the brain you need for essential tasks, like movement or speech. This is important to know, as it indicates whether surgery to help your epilepsy would put these functions at risk.

How the doctors decide if you need this procedure

Once the Epilepsy team has seen all the results from previous tests they will discuss whether invasive monitoring will also help them to decide whether surgery is an option for you. You will need to attend a joint epilepsy and surgery outpatient clinic to discuss this with the team. You will also be able to meet the surgeon and he or she will explain the risks and benefits of the test to you. 

The Epilepsy team will then ask you to think about the information given to you and decide whether you want to have the test.


You will be given a general anaesthetic for the operation to put the electrodes in place. Healthy children usually cope well with the anaesthetic, but the risk increases if you have other health problems.

However, the specialist doctors (anaesthetists) who look after you during the operation will keep any risks to a minimum. You may feel sleepy, dizzy or sick afterwards but this usually doesn’t last long. You might need medicine to stop the sickness. This operation has a slightly higher risk of infection than others, but again, the doctors and nurses will do all they can to prevent this.

After the operation to put the electrodes in place, it is sometimes necessary to reduce or stop your anticonvulsant (anti-epilepsy) drugs during the days of invasive monitoring. This is so that you are more likely to have a seizure while in hospital. The doctors will decide this with you when you come into hospital for the test.

If you have had a number of seizures recently, even though you are taking anticonvulsant (epilepsy) drugs, you may be able to continue taking them during the test. There is always a risk in reducing or stopping your drugs suddenly for this test, as it may cause you to have a longer or more intense seizure than usual. However, the doctors and nurses will monitor you closely to try to stop this from happening.


Your doctors can tell a lot from an EEG and other tests and brain scans, but invasive monitoring can help them to be sure exactly which part of your brain is responsible for the epilepsy. This is particularly helpful where brain scans have not shown an abnormality or where the doctors are concerned that seizures may be starting near an area that is also controlling one of your useful functions.

Any complications?

You may feel sleepy after the operation to have the electrodes inserted, but this usually passes. You may notice that your face seems swollen, but this is temporary and will return to normal after the test. You may also feel and be sick after the operation to insert the electrodes and you may need some medicine to stop this.


You will need to come into hospital the day before you have the operation to put the electrodes in place. This is to make sure that you are well enough to have the operation. You may also need a further MRI scan to help the doctors decide exactly where to put the electrodes.

A doctor will examine you and take a blood sample to check that your blood levels are fine. The doctors will explain about the test in more detail, discuss any worries you may have and ask you and your parents to sign a consent form giving permission for you to have the operation. Another doctor will also visit you to explain about the anaesthetic.

Many of the studies we perform involve the use of x-rays. All girls aged 12 years or older are tested to make sure they are not pregnant on the day of their procedure. If they are found to be pregnant the doctor will decide if the procedure should be delayed or cancelled.

If you have any medical problems, for instance, allergies, please tell the doctors about these. If you have had any infectious diseases like chicken pox or head lice recently, please tell the doctors. Please bring any medicines that you are taking, and show these to the doctors.

The evening or the morning before the operation, you will need to have a bath and a hair wash with a special soap.


The operation to insert the electrodes will be carried out under a general anaesthetic. This means that you will not feel any pain during the operation. If you need electrode grids, the surgeon will open up your skull to place the grids over your brain. This involves making a small flap to fold the skull back into place and secure it.

If you need electrode strips, the surgeon will drill small holes in your skull to thread the strips over your brain. After the operation, you will have many wires coming from the wound in your head. These wires will be fastened with tape and bandages so that they cannot be pulled out of place while you are on the ward.

Also, you will have a nurse with you 24 hours a day to make sure this does not happen. You will have a CT scan immediately after the electrodes are inserted to check exactly where they are.

Once the operation to insert the electrodes is over, you will stay on a ward in one of the telemetry rooms. You will be connected to the EEG and video monitoring equipment for up to 10 days, while the technicians confirm which area of the brain is causing your seizures.

The team will let you know if the doctors are planning to carry out functional brain mapping. This involves the technicians and doctors stimulating areas of the brain by way of the electrodes. This will make sure that none of the areas of the brain which are planned to be removed have important functions, especially for movement in the hands or legs.

You will have your own nurse for this time who will look after and monitor you closely. He or she will take various measurements like blood pressure and heart rate every hour while the electrodes are in place and also take blood samples for testing. You will probably have a drip until you are drinking enough fluids.


Once the technicians have carried out all the monitoring, the epilepsy team will discuss the results with you. This will include whether the area responsible for seizures has been located, whether an operation can be offered and what risks there are.

If you, with the team, decide that removing an area of the brain could help you, this will take place at the same time as the removal of the electrodes. If it is felt not to be of benefit to remove any brain tissue, surgery will take place just to remove the electrodes.

Finding out more

This information does not mean that the same treatment will be carried out in every hospital. Nor does it replace health or medical advice. If this is a treatment that you or your family are considering please contact the Epilepsy team at GOSH.

Compiled by:
Great Ormond Street Hospital
Last review date:
December 2013