Department of Neurology, Miami Children's Hospital, 3200 SW 60th Court, Miami, Florida 33155, USA.
Children with medically resistant epilepsy are often referred for surgical evaluation. The absence of a specific focal lesion on MRI may render the work-up difficult. In response to the need to localize the primary area of epileptogenesis, surgery protocols are being developed which rely on clinical semiology, EEG and functional imaging data. In selected cases, intracranial EEG monitoring may be required. While testing more often depends on the convergence of modalities, it is possible to localize seizure origin in the majority of children, and fully excise the epileptogenic region. This review presents the etiology and preoperative modalities available for children with intractable, non-lesional epilepsy.The presence of gross structural lesions greatly facilitates the preoperative evaluation of intractable seizures. While a structural lesion may not prove seizure origin, it nonetheless implicates one brain region as the source of seizure origin, and may add additional information about its underlying substrate. Furthermore, a lesion may lie adjacent to eloquent cortex, signaling that complete removal of the epileptogenic zone may be difficult or impossible. The occurrence of multiple lesions is indicative of a more diffuse process, and preoperative studies must select the primary epileptogenic abnormality and estimate potential seizure activation at other sites. Children referred for epilepsy surgery often have normal or non-specific imaging findings. These "intractable non-lesional" epilepsy (INLE) patients are extremely challenging as they typically present with severe epilepsy, and are as prone to deterioration as lesional cases. In response to the lack of structural imaging data, surgery protocols have been developed that rely on clinical semiology, EEG and functional imaging data to define the epileptogenic zone.