Dr RDC Elwes, Department of Clinical Neurophysiology, King’s College Hospital
Advances in structural imaging and of surgical technique have had a major impact on the use of EEG in epilepsy surgery. The majority of cases with hippocampal sclerosis, or lesions such as cavernomas or indolent glioneuronal tumours, are now operated if the scalp EEG findings are congruent and the lesion can be removed without risk of deficit. Intracranial EEG to assess medial temporal epilepsy is now less frequently performed. Those with TLE and bilateral disease, atypical electroclinical features (often termed temporal plus epilepsy), and those with normal MRI may need invasive evaluation. A larger number of patients with cortical dysplasia are now seen, often with frontal or perisylvian epilepsy. A significant number have normal structural imaging. The lesion, when visible, may be subtle, often at the bottom of a sulcus and the extent uncertain. This has led to a greater use of stereoEEG with multiple depth electrodes implanted using robotic surgical techniques. Placement is often guided by functional imaging. Many predicted that high resolution MRI would obviate the need for intracranial EEG. By a curious paradox the reverse appears to have happened and streoEEG is now much more widely performed. The increasing use of neural stimulation to treat epilepsy has had a similar effect. The historical development and current use of EEG in epilepsy surgery, particularly invasive evaluation, will be reviewed.