Neurology

Strong Epilepsy Center

Tests - Intracranial Electrodes

Invasive or intracranial electrodes are recommended when monitoring from electrodes placed on the scalp and in the cheeks does not provide enough information. The procedure is called invasive because the electrodes are placed inside the skull. Intracranial electrodes are placed on the surface (cortex) of the brain.

There are two types of intracranial electrodes: cortical strips and grid electrodes. Patients can have one or both of these.

Cortical Strips are put in place by the neurosurgeon, in the operating room, while you are under general anesthesia. The night before surgery, the patient's head is shaved. During surgery, a small incision is made in the scalp and a small hole is drilled in the skull. The neurosurgeon inserts the strip electrodes through this small hole. The electrodes rest on the surface of the brain.

After the surgery, you will have an X-ray and a CT scan. Then you will go to your room. You will probably have a headache for a few days and may take pain medication.

Long Term Monitoring will begin as soon as possible, usually the afternoon or evening of your surgery. The wires from the implanted strips will be connected to the equipment rack in your room. Long Term Monitoring will proceed as usual. Your EEG will be recorded from your implanted strips.

Your medication will probably be lowered to bring on seizures. Special procedures, involving other medications, may be required. If this is necessary, your physician will explain the procedures to you.

The strip electrodes will be in place for 7-14 days. After your Long Term Monitoring is complete, the neurosurgeon will remove the strips. This procedure is minor and may be performed either in your room or in the operating room while you receive intravenous sedation.

Grid electrodes allow us to map an individual's brain. We can find the exact areas of your brain involved in your seizures. We can also find language, muscle movement and sensation areas.

Grid electrodes are put in place by the neurosurgeon, in the operating room, while you are under general anesthesia. In preparation, the night before, your head is shaved. The grid is much larger than the strip electrode and a larger opening must be made in the skull in order to insert it. Like the strip electrode, the grid rests on the surface of the brain.

After surgery, you will have an X-ray and a CT scan. You will probably spend a day in the intensive care unit before returning to your room. Most patients have a headache and feel groggy for a few days.

Long Term Monitoring will begin as soon as possible. The wires from the grid will be connected to the equipment rack in your room and Long Term Monitoring will proceed as usual. Your EEG will be recorded from the grids. Your medication will probably be lowered to bring on seizures.

Usually, brain mapping is done on the third through the sixth day. Through the grid electrodes, the neurosurgeon will stimulate various brain regions in order to identify areas responsible for movement, sensation and language.

The information that we gather helps us plan your epilepsy surgery. Our goal is to preserve important functional areas while we surgically eliminate the areas responsible for your seizures.

The grid is left in place for 7-14 days. It is removed by the neurosurgeon, in the operating room, while you are under general anesthesia. This is usually done at the same time as your resective surgery (temporal lobectomy or extratemporal resection).

The neurosurgeon will give you detailed instructions on how to prepare for the surgery. The general instructions in the Long Term Monitoring brochure will apply to your hospital stay. You may want to bring some kind of head covering to wear home from the hospital.

Consent forms are required for these procedures. The neurosurgeon will answer any questions you may have.