LEARN ABOUT THE TESTS

Understand all possible surgery options early

There are many tests that are done to see which epilepsy surgery is best for your child. The tests are done in two phases. Some require several days in a hospital. Others can be done in an appointment. Doctors then review all the tests together to answer your questions about epilepsy surgery.

 

Now that your child has been referred for a surgical evaluation, what exactly does this involve? Surgical evaluations usually occur in two phases:

Phase 1 Epilepsy Surgery Tests

Phase I involves tests that are non-invasive. This means that doctors do not need to open the skull or drill small holes in it to study the brain. Non-invasive tests do not require surgery such as craniotomy or burr holes.

These tests try to find the area of the brain where seizures start. They also help doctors understand how seizures affect your child.

Your child may not need to have every test available as part of Phase I presurgical evaluation. Doctors will decide which tests are necessary.

Video electroencephalography (EEG) monitoring in epilepsy monitoring units (EMU)

If your child has been diagnosed with seizures, he or she has already had at least one EEG. Your child’s EEGs may have been an hour or so long and performed in an outpatient setting, meaning you didn’t have to stay in the hospital to have the EEG.

The purpose of the video EEG in the epilepsy monitoring unit is to record your child’s seizures on the EEG while capturing the seizures on video to help the medical team pinpoint the surgical focus. This test requires electrodes which attach to your child’s scalp with a special type of glue. Your child will be admitted to the hospital for several days so that the team can get a complete picture of your child’s seizures and brain activity day and night.

Sometimes the video EEG, even after several days of recording, does not give the team enough information. If it’s still unclear where your child’s seizures start or spread, the team may decide to place more electrodes on your child’s scalp. This is called high density EEG. In this type of test, the electrodes are placed 10 millimeters apart or less to help record electrical activity from more parts of the brain.

Magnetic Resonance Imaging (MRI)

MRI is a test used to take a detailed image of the brain in order to identify any abnormal areas that could be causing the seizures. It is these abnormal areas which the surgeon might attempt to remove or disconnect if surgery is later recommended. Most centers have powerful MRI machines and special techniques that can find very subtle abnormalities.

Your doctor will like order special types of MRI sequences. It’s important that an epilepsy protocol is used. This helps capture the right images of your child’s brain. Your child will likely need anesthesia or sedation for this test so that they do not move during imaging.

An MRI is a strong magnet that uses radio waves to send signals to and from the person who is being scanned. These signals are turned into images by a computer attached to the MRI. The magnet strength is measured in a unit called “Teslas,” often shortened to “Ts.” The higher the “T,” the more clear and detailed the image will be. Phase I MRIs are either 1.5T or 3T. 3T is considered best for an epilepsy surgery workup, but there are some circumstances where the 3T machine is not preferred. (Some facilities have 7T MRI, but these are typically used for research only.) It is important to discuss the choice of MRI machine with your doctor when the test is ordered.

Some brain malformations are not always apparent, or the viewable lesion may be part of a larger abnormality that does not show up on MRI . These malformations often do not appear on MRI until years later when the child’s brain is larger or more myelinated. Sometimes, for example, cortical dysplasia is never seen on MRI and it is not discovered until the brain matter is sent to the pathology lab that cortical dysplasia is confirmed.

  • It’s important that your child’s MRI is read by an experience neuroradiologist. Inexperience can result in negative MRI readings.
  • Negative MRI readings can also occur if the seizures are caused by genetic or metabolic issues.
  • Further Phase I testing, and sometimes invasive Phase 2 procedures, may be needed if your child has a negative MRI.

Phase 1 Evaluations: Part 1

Our founder Monika Jones discusses phase 1 evaluations with Dr. Elaine Wyllie, a pediatric neurologist at The Cleveland Clinic. Dr. Wyllie reviews when parents should consider surgery, and then introduces us to the many aspects of phase 1 evaluations including how MRIs are not 100% reliable when exploring lesions and malformations in the brain. Subtle or invisible lesions require further assessments including PET, SPECT, and MEG.

Phase 1 Evaluations (Part 2): PET, SPECT, MEG, and Wada

Our founder Monika Jones discusses phase 1 evaluations with Dr. Ahsan Moosa Valappil, a pediatric neurologist at The Cleveland Clinic. Dr. Valappil reviews the various phase 1 evaluations beyond EEG and MRI. These evaluations include PET, SPECT, and MEG, as well as functional evaluations such as fMRI, Wada test, and MRI with diffusion tensor imaging.

When The Structural MRI Looks Good:

Dr. Elaine Wyllie, renowned neurologist at the Cleveland Clinic, and author of several books on epilepsy, explains the various forms of pre-surgical tests, including structural MRI, functional MRI, ictal SPECT, PET, EEG, MEG, and discusses various difficult case studies, such as where the MRI does not reveal a brain malformation.

Positron emission tomography (PET)

Some surgical centers may use PET scans to look at the metabolism of the brain. Metabolism is the process by which your body converts what you eat and drink into energy. The areas where the seizures begin often show hypometabolism, or slower metabolism that the rest of the bran. PET is often helpful in finding brain abnormalities for those people who have normal MRIs. Learn more…

Single-photon emission computed tomography (SPECT)

A SPECT scan may also be used. A SPECT is a type of scan that shows the areas of increased blood flow in the brain when a seizure begins, which helps the medical team find the area of the brain where the seizures begin. Learn more …

Magnetoencephalography (MEG)

MEG is a type of imaging test that locates brain activity and measures magnetic fields created in the brain. This scan is used to produce an image that identifies the source of seizures.

Unlike MRI, MEG scanners are quiet. Results from the MEG test are then matched up with an MRI. This process creates a map that shows normal and abnormal areas of the brain. A MEG scan may be requested by the neurosurgeon to identify the source of the seizures if other scans are inconclusive.

What is magnetoencephalography (MEG)?

This video from MEGIN, makers of MEG machines, gives an easy-to-understand explanation of how a MEG machine can help find areas of the brain that are causing seizures.

One Parent’s Journey With MEG For Her Daughter’s Presurgical Evaluation

Parent Elaine O’Loughlin shares how using MEG helped localize her daughter’s seizures.

Wada testing or intracarotid sodium amobarbital procedure

A Wada test, or intracarotid sodium amobarbital procedure, may be used to determine which side of the brain is processing your receptive and expressive language as well as memory. This test does not require a craniotomy. Sodium amobarbital is injected into your child’s carotid artery, and for several minutes, the functions of the left side of your child’s brain will be stopped so that the right hemisphere can be tested. Learn more …

Transcranial magnetic stimulation with fMRI

Some surgical facilities have the capability to determine functional mapping using a combination of transcranial magnetic stimulation and fMRI. This allows the team to determine where motor function is localized in the brain.

Neuropsychological assessment

A neuropsychologist is a non-medical doctor who tests your child’s brain functions such as language, memory, and attention, through a series of tests. Depending on your child’s age and cognitive ability, a pediatric neuropsychologist may assess your child to determine the nature and extent of brain dysfunction caused by seizures and/or anti-epileptic drugs.

Neuropsychological Assessments Before and After Epilepsy Surgery

Clinical neuropsychologist Mary Lou Smith, PhD, member of the International League Against Epilepsy’s Neuropsychology Task Force, discusses the importance of neuropsychological assessments including in epilepsy surgery evaluation.

Phase 2 Epilepsy Surgery Tests

After the Phase I evaluation, your child’s medical team will decide the next steps. Sometimes, it is very clear at this point if the child is a good candidate for surgery. Other times, there is uncertainty, and more testing is needed.

This next step is called a Phase II evaluation. Phase II evaluations are invasive. This means that the surgeon will need to open up the skull or make small holes in the skull to plan implant the electrodes.

Phase II involves another video EEG, but this time, the electrodes are directly on the brain or through the brain matter. Because this requires surgery, it is important to discuss potential risks with the team before you proceed.

Electrode implantation

Subdural (also known as electrocorticography)

A subdural electrode grid (often referred to by doctors and families as ‘grids’) is a thin sheet of material with many very small electrodes in it. The grid is placed directly on the surface of the brain, and a VEEG is performed in an epilepsy monitoring unit. The advantage of the subdural grid is that it can give you a more accurate picture of your child’s brain activity because it is directly on the brain, rather than performing the EEG through layers of bone, skin, fat tissue, and muscle as you had in Phase I VEEG.

Depth

Depth electrodes are electrodes on small wires that are implanted in the brain and can pick up EEG activity from deep inside the brain.

Combination

Sometimes, it is appropriate to implant a combination of depth and subdural electrodes.

Stereoelectroencephalography (stereoEEG)

With the stereoEEG approach, several depth electrodes are implanted in a pattern that is customized to surround the seizure focus and help the medical team to understand the seizure-producing area in a three-dimensional way. Learn more…

Cortical stimulation or functional mapping

Cortical stimulation mapping, also known as functional mapping, is usually performed in patients who have been implanted with subdural electrodes. After seizures are recorded, electrical stimulation is briefly and painlessly sent through the electrodes separately to identify how the part of the brain underneath the electrode functions normally. The purpose of functional mapping is to determine if the area of surgical focus overlaps with areas of the brain that control important sensory, language, and motor functions. If necessary, surgery can be planned to minimize the damage to these functional areas.

RISKS OF PHASE II MONITORING

Anesthesia

Several Phase II tests require the use of sedation or general anesthesia. General anesthesia carries with it a very small risk of death.

Expected side effects of craniotomy

Common side effects of craniotomy include some facial swelling. The eye adjacent to the craniotomy incision may swell shut for a few days. Children are often nauseous from the anesthesia and may not eat or drink fluids for a few days.

Research shows that pain can be moderate to severe in 90% of patients the first several days after the procedure. The incision site is usually managed with morphine or similar strong medications for a day or two and then with ibuprofen or acetaminophen. A craniotomy pain plan should be discussed with your child’s team prior to Phase 2 monitoring.

Approximately 30% of patients develop chronic headaches.

Depending on the size of the craniotomy, a drain may be placed under the skin to evacuate any fluid build up from the incision site.

Craniotomy risks

As with any surgical procedure, complications may occur after craniotomy. General complications include::

  • Infection, including meningitis and pneumonia
  • Bleeding
  • Blood clots
  • Unstable blood pressure
  • Stroke
  • Brain swelling
  • Seizures
  • Muscle weakness
  • Leaking of cerebrospinal fluid
  • Problems with electrolyte regulation

Phase 2 Evaluations: Invasive evaluations

Our founder Monika Jones discusses phase 2 invasive evaluations with Dr. Taylor Abel, Director of the Pediatric Epilepsy Surgery Program at UPMC Pittsburgh Children’s Hospital. Dr. Abel reviews the various phase 2 invasive evaluations sometimes required to localize seizures in the brain, including stereo EEG, grids, and depth electrodes.