The most common form of epilepsy treated with surgery are partial seizures, which begin in a specific brain region. Even seizures that spread throughout the whole brain, such as "grand mal" or "tonic-clonic convulsions" usually begin in one well-defined part of the brain (e.g. they begin as partial seizures). These seizures can be controlled with epilepsy surgery. The area of the brain where the seizure begins is considered epileptogenic or abnormal, so recurrent refractory seizures can be controlled by surgically removing this abnormal region of the brain. An important aspect of staged epilepsy surgery involves functional mapping of eloquent cortex whereby the brain is tested before an area is removed to be sure it is safe for removal. Often, because the area where the seizure begins is abnormal, the area is not providing any useful function.
Specialized studies performed at our center will help to accomplish the important tasks. There are several methods epileptologists and epilepsy surgeons use to localize the seizure onsets and to map brain functions. This is to assure that the seizure focus resection is safely accomplished. The preoperative work-up may include non-invasive tests such as Magnetic Resonance Imaging (MRI), Positron Emission Tomography (PET), Single Photon Emission Computed Tomography (SPECT), Magnetoencephalography (MEG), and Video-EEG (VEEG). By helping to visualize abnormal anatomy and physiology associated with or responsible for seizure onset, a surgical target is defined. Video-EEG recording is the most important test used to characterize seizures and provide possible seizure localization. There are also invasive tests that involve placing the electrodes directly on the surface or in the brain. These methods may be necessary to provide accurate seizure onset location and is the most accurate method for defining epileptogenic and normal functioning brain regions.
No single test is definitive and can tell us everything we need to know. However, by accumulating information from different sources that confirm and supplement each other, we are able to accurately and safely perform the surgery.
Noninvasive tests are ones that do not invade the body or require a surgical procedure and, in general, involve little or no risk. The assessment includes:
The preoperative tests may also include invasive tests. Invasive tests are ones that invade the body. Technically, the insertion of a needle into a vein to draw blood is an invasive procedure, but it is so common and safe that it is not considered invasive. In general, invasive tests are associated with some risk, but the risk varies dramatically with the different types of tests and procedures. The following is a comprehensive list of preoperative tests performed at the NYU Comprehensive Epilepsy Center: