The Surgical Evaluation Process

The Surgical Evaluation Process 2017-11-28T20:21:22+00:00

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

PHASE I

Phase I involves non-invasive tests. Non-invasive tests do not require surgery.  Not every patient requires every test available in the Phase I evaluation.  Your child’s doctor will decide which tests are necessary during the Phase I evaluation.

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.

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, known as an epilepsy protocol, to 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.  

A Note On MRIs

Sometimes, abnormalities in a child’s brain are very subtle to even the most expert radiologist interpreting the MRI image. Therefore, it is important to know what kind of MRI machine is being used for your child’s MRI. Simply put, 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.

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.

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.

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.  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.

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.

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.

PHASE II

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 involves another video EEG, but this time, the electrodes are placed inside the skull. Since this requires surgery, it is important to discuss potential risks with the team before you proceed.

There are different ways to do Phase II monitoring.  All require a craniotomy and electrode implantation.

A craniotomy is the surgical removal of part of the bone from the skull to expose the brain. The section of bone, or bone flap, is temporarily removed, then replaced after the brain surgery has been completed. 

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.

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. Pain at the incision site is usually managed with morphine or similar strong medications for a day or two and then with ibuprofen or acetaminophen. 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

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