Invasive monitoring of limbic epilepsy using stereotactic depth and subdural strip electrodes: surgical technique

In spite of advances in noninvasive localization of seizure foci, some cases of intractable limbic epilepsy still require invasive recordings in order to identify the site of seizure onset. This necessitates a safe and reliable method for placing depth and subdural electrodes in the mesial temporal and orbitofrontal regions. The University of Florida has devised a system that utilizes CRW-based stereotactic placement of bitemporal depth electrodes in conjunction with placement of subdural strips over the inferolateral temporal lobe and orbitofrontal cortex. This report describes the surgical technique and initial clinical experience using this method.

Depth electrodes are placed along the long axis of the hippocampi via an occipital approach. A CRW-based stereotactic system was developed that incorporates both computed tomography (CT) and magnetic resonance imaging (MRI) for selection of target and entry sites and displaying the electrode trajectory. Subdural strip electrodes are placed over the inferolateral temporal and orbitofrontal regions through burr holes.

This method has been used in 18 patients (depth electrodes only in three patients and depth electrodes with subdural strips in 15 patients). This information lead to surgical resections in 15 patients. No resection was recommended in three patients (two with bitemporal onset and one with no seizures after 6 weeks). Complications were limited to an unplanned removal of one electrode and an asymptomatic lateral temporal lobe contusion in one patient.

This method provides a safe and effective way to sample bilateral mesial temporal and orbitofrontal regions in cases of intractable limbic epilepsy.