Insular epilepsy surgery under neuronavigation guidance using depth electrode

The unfavorable surgical results that have been reported with insular epilepsy surgery may be related to inadequate monitoring. Insular epilepsy surgery requires the precise monitoring and tailored removal of the epileptic zone. The purposes of this study were to precisely monitor the hidden cortex and determine the effectiveness of using different monitoring methods, including subpial depth electrodes. This is a study of a single center series of six patients (three men, three women) who underwent insular surgery between May 2006 and December 2007. All patients had experienced medically intractable seizures without any evidence of a tumorous condition based on previous examination. We used strip electrode implantation in one patient and stereotactic depth electrode insertion in two patients, which resulted in partial removal of the insular. The other three patients underwent open direct subpial depth electrode insertion, which resulted in total removal of the insular cortex. There were no surgery-related complications with the insulectomy after insertion of the subpial depth electrodes, regardless of the monitoring method or extent of removal. All patients except for one showed considerable improvement in epilepsy (83.3% Engle class I, 16.5% Engle class II). In the three patients who had open direct subpial depth electrodes inserted, we achieved total insulectomy without increasing the surgical morbidity, while in the other three patients, the insular removal was only partial. We demonstrate that image-guided insular surgery with safe and accurate depth electrode guidance results in an optimal outcome and complete resection of the insular cortex.