Conclusion

The 20 chapters in this book offer a comprehensive review of currently available knowledge regarding epilepsy surgery in MRI-negative patients, and they suggest that we have entered a novel era for treating these patients with the most challenging epilepsies. Three primary messages in this book deserve to be emphasized. The first message is that re-evaluation of MRI data, either through optimal acquisition (more sensitive sequence, higher-field strength), post-processing tools, coregistration with other modalities (especially FDG-PET), and expert reassessment, enhances the detection of a large proportion of MRI-negative pathologies, such as focal cortical dysplasias (FCD) (Chapter 3). Up to 89% of small FCD overlooked by experts could be detected by using sophisticated post-processing methods of 3D-T1 MR images, coupled with neural networks automatic detection (Chapter 3). The second message relates to the conceptual framework of presurgical evaluation. In patients with refractory focal epilepsy whose MRI discloses a well-defined epileptogenic lesion, presurgical evaluation concentrates on refining the localization of the epileptogenic zone (EZ) to be resected. In MRI-negative patients, presurgical evaluation also needs to provide insights into the underlying pathology for several reasons: (i) the presence and type of underlying pathology have a strong impact on the chance of postsurgical seizure freedom, with optimal surgical outcome in focal cortical dysplasia (FCD) type II and end- folium sclerosis, and poorest outcome in patients with histologically normal resected tissue; (ii) the extent of the EZ varies with the underlying pathology, being usually circumscribed to a sulcus in MRI-negative FCD type II, and often much more extensive in FCD type I (Chapter 11); and (iii) interpretation of presurgical data, such as the presence or absence of a clear-cut interictal hypometabolism on FDG-PET, will differ as a function of the suspected pathology. In other words, the “what” appears as important as the “where” when contemplating surgical treatment of MRI-negative patients.