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 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.
There are different ways to do Phase II monitoring. All require a craniotomy and electrode implantation on or into the brain. 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.
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 electrodes are electrodes on small wires that are implanted in the brain and can pick up EEG activity from deep inside the brain.
Sometimes, it is appropriate to implant a combination of depth and subdural electrodes.
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
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.
As with any surgical procedure, complications may occur after craniotomy. General complications include::
- Infection, including meningitis and pneumonia
- Blood clots
- Unstable blood pressure
- Brain swelling
- Muscle weakness
- Leaking of cerebrospinal fluid
- Problems with electrolyte regulation