Subdural EEG has a high sensitivity for detecting interictal spikes. The irritative zone is usually more extended than the seizure onset zone. Removal of the entire irritative zone improves outcome in extratemporal as well as neocortical and tumour-related temporal lobe epilepsy, but not in mesial TLE. Quantification of spike features like amplitude, frequency, or latency may help differentiate the localizing and prognostic value of different spike populations. Although EEG patterns are not aetiology, some pathologies such as focal cortical dysplasias are frequently associated with typical EEG patterns, in which case intraoperative electrocorticography should be applied to tailor resections. Presence of a focal seizure onset zone and slow propagation are associated with good surgical outcome. Definition of a sound hypothesis about location of the seizure onset zone from pre-invasive findings is a crucial prerequisite for the success of subdural recordings. Concordance of interictal and ictal recordings is highly predictive of outcomes.
Surgical outcome of cortical dysplasias presenting with chronic intractable epilepsy: A 10-year experience