Application of stereotactic concepts to the surgery of epilepsy.

For the authors, the essential feature of stereotaxis is the three-dimensional representation of the entire brain, including the central gray nuclei as well as the cerebral cortex. Stereotactic neurosurgery, which in this conception might be called "global", associates data from indirect localization (basic reference lines, proportional grid) to direct individual localization (performed by bidirectional, orthogonal teleradiography, with stereoscopy). The obtained high precision radiographic documents allow to establish the three coordinates (X, Y, Z). This method, also used in localization of tumours and interstitial irradiation of tumours, led to the definition of a special methodology for epilepsy surgery (threefold correlation of the clinical seizure patterns, electrical anomalies and the concerned anatomical structures). The stereotactic implantation of several acute and chronic electrodes (stereo-EEG) gives a 3-dimensional definition of the epileptogenic area and of its propagation pathways. These data, as well as the individual anatomy of the patient's brain are represented by the neurosurgeon on a surgical diagram. The transfer of these data to the surgical field is facilitated by the accuracy of the diagram. A double postoperative control is made (photographs--teleangiography). The described methodology increases the precision of open surgery. It is also used to localize and to remove "incipient" lesions evidenced by the CT scan (accurate anatomical localization--vascularization). In the opinion of the authors, the use of a common stereotactic geometry applied to the collection of paraclinical data will lead in the future to an increased precision of surgery and hence, to a better respect of the brain and of its function.