THE UTILITY OF PLACING SPHENOIDAL ELECTRODES UNDER THE FORAMEN OVALE WITH FLUOROSCOPIC GUIDANCE

Although sphenoidal electrodes are widely used to detect epileptiform activity, there is no agreement on an optimal target to which electrod es should be aimed. The purpose of this study was to determine whether fluoroscopic guidance is a reliable method for placing electrodes dir ectly below the foramen ovale and whether such positioning enhances th eir capacity to detect epileptiform activity when compared to similar electrodes placed blindly into the infratemporal fossa. We examined th e surface/sphenoidal EEG recordings of 17 patients with intractable pa rtial seizures of anterotemporal origin, after fluoroscopically placed sphenoidal electrodes (FPSE) had been inserted to lie just below the foramen ovale. A criterion for eligibility was a previous prolonged vi deo/EEG monitoring with blindly placed sphenoidal electrodes (BPSE) th at failed to detect seizures with a focal onset, No blindly placed ele ctrode, for which there was radiographic documentation, reached the fo ramen ovale. Fluoroscopic guidance assured accurate targeting. FPSE de tected a unilateral anterotemporal interictal focus in four patients i n whom BPSE had failed to record any interictal spikes and detected bi temporal independent interictal foci in one patient in whom BPSE had i dentified only unilateral spikes. In nine other patients, the spike co unt obtained with FPSE recordings increased by >100% when compared to that obtained with BPSE recordings. FPSE recorded seizures with an ant erotemporal focal onset pattern in 10 patients in whom BPSE had record ed seizures with a regional, lateralized, or nonlocalized onset patter n. In nine of these 10 patients, this was adequate to recommend surger y and avoid invasive monitoring. Fluoroscopic guidance assures accurat e targeting of the foramen ovale. When compared to BPSE, FPSE resulted in better detection of interictal and ictal epileptiform activity of mesial-basal-temporal origin.