Chapter 51 - Invasive evaluation

In most of epilepsy surgery centers, the overall proportion of epilepsy surgery candidates evaluated by invasive recordings has decreased over the last decade. However, the subset of patients who can benefit from the use of intracranial electrodes remains significant, especially in the most specialized centers where difficult cases are preferentially referred. Importantly, an increasing number of patients who were not considered in the past as ideal candidates now can benefit from invasive recordings. These are performed using grids, strips, depth electrodes, or a combination of them, with the common goal to better define the cortical areas to be resected (ictal onset localization) and/or to minimize the risks of post-operative unacceptable deficits (functional mapping). We will discuss, in the following sections, the advantages and limits of these different types of intracranial recordings, their risks, their indications, and the way to define the ictal onset zone. Emphasis is put on the importance of clear questions before electrode implantation, and on the necessity of a patient management multidisciplinarity conference concerning which patients require the use of invasive recordings, what type of electrodes are appropriate, where the electrodes must be placed, and whether the patient is likely to benefit from surgery.