Dipole reconstruction as a method for identifying patients with mesolimbic epilepsy.

The aim of the study was to evaluate whether or not dipole analysis of extracranially recorded epileptiform activity, using a spherical three-shell head model, may distinguish epilepsy of mesolimbic origin from origins of other locations. Dipole analysis was performed on previously extracranially recorded interictal epileptiform discharges in 22 patients investigated for ictal onset patterns with subdural electrodes over one or both subtemporal areas. The dipole results in two groups of patients were compared. Group A contained patients in whom the subdural investigation showed subtemporal seizure onset (indicating mesolimbic epilepsy) ipsilateral to the dipole locations. Group B contained patients in whom seizure onset was other than ipsilateral subtemporal, or in whom seizure onset could not be determined. Group A patients had uniform dipole results, with an oblique posterior, slightly elevated dipole orientation, and an anterior temporal dipole location. Group B patients had more variable dipole results. If dipoles with anterior temporal location, and oblique posterior and elevated orientation are obtained, epilepsy of mesolimbic origin should be suspected. If the dipole locations or orientations markedly deviate from this pattern, the epileptogenic region is likely to be other than mesolimbic.