VIDEO-EEG MONITORING
Phase I Pre-Surgical Evaluation
Pre-surgical V-EEG is performed on patients with a known or strongly suspected focal seizure disorder (seizures that stem from one distinct area of the brain) in whom epilepsy surgery is a treatment consideration. Patients are admitted for at least 5-7 days, in order to record a sufficient number of the patient’s typical seizures. The objectives of the phase I pre-surgical evaluation are 1) to be able to reliably and accurately determine the side of the brain that seizures start from (lateralization), and 2) to determine the specific region of the hemisphere from which seizures arise (localization). While it is preferable to record seizures without making changes to the anti-seizure medication regimen, reduction of anti-seizure medication may be necessary along with other provocative procedures (sleep deprivation, hyperventilation, light stimulation, physical activity) in an effort to bring about seizures. Once sufficient data is acquired, the patient is re-started on his or her pre-admission medication regimen and discharged no sooner than 24 hours thereafter.
Often, brain mapping has to be done to identify areas of the brain that have important functions, like for example those that control movement, the senses, and speech, in order to prevent losses after surgery. Brain mapping is done through electrical stimulation of the brain. A stimulator is used; a current is delivered through electrodes that are placed on the brain (usually subdural electrodes). The intensity of the stimulation is increased systematically until function is elicited (for example, the arm moves or the patient stops speaking), seizure-like activity (after-discharges) are brought about, or the maximum intensity of the apparatus is reached. Once all electrodes are stimulated, a map with the (functional) language and motor areas among others is drawn. This map will also include the “seizure area” so the surgeon can remove it and also spare important areas of the brain.
Phase II Surgical Evaluation
Not every patient will require this evaluation stage. There are two main reasons why a patient may undergo this kind of more “invasive evaluation”. First, when the scalp EEG provides a general idea of where the seizures originate, but not a precise location. Second, when the location where the seizures originate is known, however, that area is suspected to control important brain functions (e. g. language, movement, sensation, etc.).
Phase II V-EEG involves the placement of electrodes on the surface of the brain (subdural strips or grid electrodes) or in the brain (depth electrodes). Each patient is very different and the electrodes are placed based on the results of the presurgical evaluation and recommendations of a multi-disciplinary epilepsy surgery conference. After electrode implantation, the patient undergoes continuous V-EEG as previously described, with the objective being to clearly lateralize and localize seizure onset. Once again, continuous V-EEG needs to record several typical seizures so that seizure onset can be reliably and precisely located. Once the doctors have enough information, the patient is placed on his or her pre-admit anti-seizure drug regimen (if dose reductions were made), the electrodes are removed, and, once stable, the patient is discharged. Following this phase, or alternatively, if seizure onset was clear after Phase I, a more tailored approach of intracranial electrode placement may be performed.