Presurgical evaluation: current role of invasive EEG

Background:The rationale for surgical management of epilepsies that are difficult to control with medications is to reduce or eliminate the tendency of the brain to generate uncontrolled seizures. Following successful removal of the epileptic focus patients are able to not only regain control of their seizures, but also of their independence employment and quality of life. We know that the best surgical outcome is attained after precise localization of the seizure focus. When noninvasive electroencephalography (EEG) monitoring is insufficient, invasive EEG monitoring (by means of subdural grid or depth electrodes) is sometimes necessary. Methods and Materials:There are two different techniques and types of electrodes being used to perform invasive recordings: (1) Subdural electrodes provide coverage of large areas of neocortex and are ideally suited for evaluating certain patients with intractable epilepsy, and to functionally map critical cortex. Subdural grid electrodes can be used for recording as well as for stimulating brain tissue to identify the underlying function (e.g., language areas, sensation or motor function). Placement of these electrodes requires a craniotomy. (2) Depth EEG Electrodes and stereo-EEG are those electrodes, which are placed within the substance of the brain. The neurosurgeon places depth electrodes through small burr holes and with great accuracy using a stereotactic frame. Utilizing this approach the neurosurgeon is able to place several depth electrodes in targeted brain areas, which are determined based on the results of all the presurgical noninvasive studies. Results:Patients with partial unifocal epilepsies are first line candidates for epilepsy surgery. Data from Mayo Clinic and Geneva-Lausanne Epilepsy Center showed that 60–70% of patients evaluated for epilepsy surgery finally undergo a neurosurgical procedure. About 50% of patients with focal epilepsies have temporal lobe epilepsy, and about 65–85% of these patients become seizure-free after surgery with or without continued AED treatment. Positive long lasting effect on cognition, psychosocial impact (such as driving), employment, family and social status has been noted . Unfortunately, epilepsy surgery remains underused. Discussion and conclusion:There are some limitations for invasive evaluation epilepsy surgery. We cannot record from the entire brain; some recorded activities can be difficult to localize. We cannot always achieve the goals of this evaluation. Need for an additional surgery to place These electrodes. Surgical risks including infection, bleeding and stroke and finally additional cost.