Stereoelectroencephalography: Interpretation.

Intracranial EEG has been in use for more than 50 years in the presurgical evaluation of patients with medically intractable focal epilepsy. The stereoelectroencephalography (SEEG) method has expanded very significantly over the last 5 years, in parallel with the increase in the number of complex cases (i.e., MRI-negative) being referred with medically intractable focal epilepsy to major epilepsy surgery centers. Some centers with extensive experience in subdural electrodes are indeed changing or have changed to SEEG as the principal exploration technique, which suggests that SEEG might offer specific benefits through its approach to accurately localizing the epileptogenic zone. However, interpretation of SEEG, which is a key step to its usefulness, may vary from one center to another. This may be due to different conceptual bases and the available expertise in each center. This heterogeneity in use of SEEG should be taken into account as it could contribute to erroneous conclusions and thus unfavorable outcome of epilepsy surgery. At present, there is a lack of guidelines for optimal SEEG use, although development of these is in progress. It remains challenging to translate SEEG interpretation into a practical approach to delineating surgical strategy. Identification of clear biomarkers will help in the definition of the epileptogenic zone and subsequent cortical resection. In addition, SEEG seems to be a unique tool for the in vivo investigation of human cerebral networks distributed over several lobes or sublobar structures, allowing a better understanding of their functioning.