[Indications for surgical treatment of epilepsy]

The evaluation of drug-resistant epileptics in view of causal surgical epilepsy therapy aims at accurate identification of the 'epileptogenic area'. Definition of the 'epileptogenic area', which is not synonymous or coexistent with the 'lesional area', as a positively defined area of seizure onset is obtained through the recording and analysis of spontaneous habitual seizures with electrodes placed in or close to the presumed epileptogenic brain areas. Interictal epileptiform field potentials are important too. Long-term intracranial recording techniques include direct intracerebral stereotactic depth-recording (stereo-electroencephalography, SEEG) and epicortical recordings with the use of foramen ovale as well as subdural strip and grid electrodes. The use of SEEG requires rigorous criteria, and the anatomy and vessels of the individual brain must be known in terms of a stereotactic reference system. Multi-contact flexible hollow-core electrodes are stereotactically implanted into strategically important targets, according to the evaluation strategy for a given patient. For presurgical assessment of potential candidates for selective amygdalo-hippocampectomy we have developed a less invasive extracerebral recording technique. It consists of bilateral insertion of solid four-contact electrodes via the foramen ovale, with positioning of the tips of the electrodes at the end of the ambient cistern. This technique permits stable and excellent recording from the mediobasal limbic structures of both temporal lobes. Personal experience with long-term extra-operative intracranial recording and stimulation now includes 131 patients evaluated with SEEG and 109 patients evaluated with foramen ovale electrodes.