EEG with Extracranial Foramen Ovale Electrodes
An EEG with Extracranial Foramen Ovale electrodes (EFOs) can be used to find out what part of your brain your seizures are coming from. EFOs are special EEG wires that are put through the skin to record brain waves. The purpose of this handout is to help explain what will happen before, during, and after the test.
What is an EFO?
An EFO electrode is a very thin platinum wire about the thickness of a hair. It acts like a scalp EEG electrode, but it goes through the skin and lies closer to your brain. It records more information than a scalp electrode. EFOs are placed through the skin as a pair. One will be on the left side of the face and one will be on the right side of the face. The tip of each electrode is then guided towards the bottom of the skull near a small opening called the foramen ovale. The electrode does not go into your brain. Although EFOs are more sensitive to brain waves than scalp electrodes, you will still need both kinds to help find the seizure focus. Both types of electrodes will be placed on the day you are admitted. The EFOs will be put in first. This takes place in an x-ray room.
How are EFOs Placed?
The electrode wire is threaded into a hollow, thin needle. This needle will carry the wire to its target at the bottom of the skull. The point of skin entry is in front of the ear. In the picture, the ear has been covered up by a sterile towel. The needle shaft can be seen entering the skin at the arrow point. The wire is so fine that it cannot be seen. The doctor then pushes the needle along with the wire toward the target. The target is a small opening in the skull base called the foramen ovale. It lies about 2 inches in from the surface of the skin. Once both EFOs are in place, the needles are taken out, and you return to your hospital room.
We have done this test for hundreds of patients and have had no complications yet. This does not mean that there are no risks. It means that the risks are low, but not zero. The doctor will discuss these risks with you.
Before The Electrodes Are Placed
When the date of your test is known, you will be asked to have labs drawn so that the neurosurgeon knows that you are safe to have the test. Do not eat breakfast or wear make-up on the day of admission. Do not take aspirin or ibuprofen-like products for 1 week before the procedure. Please be in Admissions by 7:30 a.m. You will go to your hospital room. Later, you will be taken to x-ray. When you arrive in the x-ray room, the neurosurgeon will explain how the wires are placed, discuss what the risks and benefits are, and ask you to sign a consent form.
If you are reading this Health Facts for You as a parent of a minor or guardian of the person who is having this test, please be prepared to go with your child or dependent adult to x-ray where you will be asked to sign the consent form. When you sign this form, it means that you agree to have the electrodes put in.
During the Placement
You will be helped onto the x-ray table and asked to lie down. The x-ray camera will be positioned over your head. The doctor will wash your face in front of your ears with iodine and mark a spot for the wires to go in. The doctor will numb the skin on your cheeks with local anesthesia. Using the x-ray pictures as a guide, the wire (mounted on the carrier needle) will be pushed into place. The needle will then be taken out and the wire taped to your cheek. Although we use local anesthesia, there may still be pain when the needle goes in. The doctor will tell you when to expect it. The pain quickly fades after the electrodes are in.
After the Placement
When both the left and the right EFO electrodes are in place, x-rays will be taken for your record. You will then be taken to your hospital room where scalp electrodes will be attached and all the wires will be hooked up to the EEG machine. Feel free to ask for Tylenol® if you have any pain from the EFOs. Report any swelling, redness, or numbness to your nurse right away. The EFOs will stay in until you are ready to go home. An EEG technologist will then remove the electrode wires in your room.
What if the EFO Electrodes Don't Reveal Where the Seizures are Coming From?
Should this happen, your doctor may wish to discuss setting up a second test using other types of electrodes. The reason we begin with EFO electrodes is because they are tolerated the best and often reveal where the seizures are coming from.
The information provided should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. A licensed physician should be consulted for diagnosis and treatment of any and all medical conditions. Call 911 for all medical emergencies. Any duplication or distribution of the information contained herein is strictly prohibited.
Last Updated: 01/07/2013
Copyright © 01/07/2013 University of Wisconsin Hospitals and Clinics Authority. All rights reserved. Produced by the Department of Nursing. HF#4271
Print Health Fact For You