SUMMARYPurpose: Focal cortical dysplasias (FCD) are localized regions of malformed cerebral cortex and are very frequently associated with epilepsy in both children and adults. A broad spectrum of histopathology has been included in the diagnosis of FCD. An ILAE task force proposes an international consensus classification system to better characterize specific clinicopathological FCD entities.

Cortical dysplastic lesions (CDyLs) are often associated with severe partial epilepsies. We describe the electrographic counterpart of this high degree of epileptogenicity, manifested by continuous or frequent rhythmic epileptogenic discharges recorded directly from CDyLs during intraoperative electrocorticography (ECoG). These ictal or continuous epileptogenic discharges (I/CEDs) assumed one of the following three patterns: (1) repetitive electrographic seizures, (2) repetitive bursting discharges, or (3) continuous or quasicontinuous rhythmic spiking. One or more of these patterns were present in 23 of 34 patients (67%) with intractable partial epilepsy associated with CDyLs, and in only 1 of 40 patients (2.5%) with intractable partial epilepsy associated with other types of structural lesions. I/CEDs were usually spatially restricted, thus contrasting with the more widespread interictal ECoG epileptic activity, and tended to colocalize with the magnetic resonance imaging-defined lesion. Completeness of excision of cortical tissue displaying I/CEDs correlated positively with surgical outcome in patients with medically intractable seizures; i.e., three-fourths of the patients in whom it was entirely excised had favorable surgical outcome; in contrast, uniformly poor outcome was observed in those patients in whom areas containing I/CEDs remained in situ. We conclude that CDyLs are highly and intrinsically epileptogenic, and that intraoperative ECoG identification of this intrinsically epileptogenic dysplastic cortical tissue is crucial to decide the extent of excision for best seizure control.

Many patients with medically refractory epilepsy now undergo successful surgery based on noninvasive diagnostic information, but intracranial electroencephalography (IEEG) continues to be used as increasingly complex cases are considered surgical candidates. The indications for IEEG and the modalities employed vary across epilepsy surgical centers; each modality has its advantages and limitations. IEEG can be performed in the same intraoperative setting, that is, intraoperative electrocorticography, or through an independent implantation procedure with chronic extraoperative recordings; the latter are not only resource intensive but also carry risk. A lack of understanding of IEEG limitations predisposes to data misinterpretation that can lead to denying surgery when indicated or, worse yet, incorrect resection with adverse outcomes. Given the lack of class 1 or 2 evidence on IEEG, a consensus-based expert recommendation on the diagnostic utility of IEEG is presented, with emphasis on the application of various modalities in specific substrates or locations, taking into account their relative efficacy, safety, ease, and incremental cost-benefit. These recommendations aim to curtail outlying indications that risk the over- or underutilization of IEEG, while retaining substantial flexibility in keeping with most standard practices at epilepsy centers and addressing some of the needs of resource-poor regions around the world.

Twenty-six patients with focal or lateralized neuronal migration disorders and intractable partial epilepsy were treated surgically. Twenty-four had reliable follow-up ranging from 1 to 15 years (mean, 5.0). Pathologically, they fell into two categories: focal cortical dysplasia (12 patients) and forme fruste of tuberous sclerosis (8 patients). In the remaining 4 patients, the material was inadequate for histological analysis. Outcome regarding seizure control was assessed according to a classification most sensitive to variations in frequency of major attacks. Ten (42%) of the 24 patients achieved good or excellent outcome, 6 (25%) had a worthwhile decrease in seizure frequency, and 8 (33%) had only discrete improvement. The variable most strongly correlated with surgical outcome was the amount of lesion removed. Seventy-seven percent of patients in whom a complete excision or excision of 50% or more of the lesion was accomplished achieved excellent or good surgical outcome. Conversely, no patient with less than 50% of the lesion removed attained the same result. There was no correlation between other clinical, radiological, or electrographic variables and outcome regarding seizure control. Specifically there was no significant correlation between the amount of excision of the epileptogenic area as judged by scalp electroencephalography and electrocorticography studies, and surgical outcome. In patients with neuronal migration disorders and intractable partial epilepsy, removal of the structural abnormality takes precedence over removal of epileptogenic tissue as the main surgical strategy to achieve seizure control.