Localization of mesial temporal lobe seizures with sphenoidal electrodes

Few studies have compared sphenoidal electrodes with scalp electrodes to determine their localizing value in temporal lobe seizures. We reviewed 76 ictal recordings with the standard International 10-20 System and T1/2 and sphenoidal electrodes from 31 patients whose subsequent intracranial EEG studies precisely localized seizures in one temporal lobe. Ictal EEGs were reviewed in a blinded fashion in both longitudinal bipolar and referential montages. Of the 23 seizures in 11 patients with mesial temporal lobe epilepsy (MTLE), all seven seizures in 3 patients were localized exclusively to one sphenoidal electrode, before involvement of T1/2 and temporal scalp electrodes. The remaining 16 seizures from 8 MTLE patients and all 53 seizures in the 20 patients with neocortical temporal lobe epilepsy (NTLE) had simultaneous involvement of sphenoidal, T1/2, and temporal scalp electrodes at seizure onset when analyzed with referential montages. Sphenoidal electrodes may provide valuable localization data for presurgical evaluation of patients with possible TLE. In particular, seizure rhythms confined to the sphenoidal electrode at ictal onset, without involvement of scalp electrodes, occurred only in patients with MTLE (p < 0.04). Further studies comparing these electrodes with other types of surface electrodes are needed.