Presurgical focus localization in epilepsy

Success of epilepsy surgery depends on adequate identification of the epileptogenic zone, the brain area responsible for generating seizures. The presurgical workup involves the use of numerous diagnostic methods to allow accurate localization of this area. The aim of this thesis was to improve our knowledge of presurgical diagnostic approaches in epilepsy surgery by evaluating the use and accuracy of current and novel diagnostic methods for focus localization. We surveyed the used diagnostic imaging, post-processing, and electric and magnetic source imaging techniques throughout European epilepsy surgery centers and found a large variation between centers. Also, few conduct their presurgical diagnostic pathway entirely in accordance with available international guidelines or recommendations. Subsequently, we reviewed the evidence-base for epileptogenic lesion localization with MRI, and for epileptic source localization with electric and magnetic source imaging. We found that results were affected by poor study quality and were likely biased towards overestimation of diagnostic accuracy and value. We therefore explored the use of novel approaches to improve presurgical workup. In a retrospective cohort of 24 surgical candidates with tuberous sclerosis we showed that interictal high resolution electric source imaging in the initial presurgical workup might complement or replace long-term video-electroencephalography monitoring. Single Pulse Electrical Stimulation by means of intracranial electroencephalography was able to on-demand identify seizure onset zone connectivity and seizure propagation pathways in six patients and may aid workup. This thesis highlights a need for high quality studies of current diagnostic methods and for further exploration of novel methods to improve presurgical evaluation.