Combined use of sphenoidal electrodes and the dipole localization method for the identification of the mesial temporal focus

We attempted to sub-classify four cases who show temporal spikes on standar d scalp electroencephalogram (EEG), using sphenoidal electrodes and the dip ole localization method. In a case with mesial temporal epilepsy, spikes sh owed phase reversal in a sphenoidal electrode, and the spike dipoles were e stimated to be in the mesial temporal lobe. In a case with lateral temporal epilepsy, spikes showed no phase reversal in a sphenoidal electrode, and t he spike dipoles were estimated to be in the lateral temporal lobe. In two cases out of four, spikes showed phase reversal in sphenoidal electrodes, w hilst the dipoles were estimated to be in the frontal lobe. Clinical featur es also suggested a diagnosis of frontal lobe epilepsy. In one of the two c ases in which frontal lobe epilepsy was suspected, ictal dipoles as well as interictal spike dipoles indicated participation of the frontal lobe in th e genesis of seizures. Nevertheless, only mesial temporal lobectomy was per formed based on results obtained by invasive subdural electrodes. As a resu lt, seizures were not controlled. Although sphenoidal electrodes were usefu l for differentiating between mesial and lateral temporal lobe foci, it is advisable to use them in combination with the dipole localization method to identify frontal lobe foci.