Accuracy of electroencephalographic dipole localization of epileptiform activities associated with focal brain lesions

We evaluated the accuracy of an electroencephalographic (EEG) localization technique (dipole inverse solution) in a consecutive series of 12 focal intracerebral lesions of diverse etiologies whose EEGs showed interictal spike activity or rhythmic activity at seizure onset. The calculated equivalent dipole was plotted on three axes in the patients' magnetic resonance image, and the distance between the dipole and the lesion margin was measured assuming that the shell of the lesion constituted an epileptogenic region. In all cases the dipole localized closer than 0.8 cm to the nearest lesion margin. In addition, we compared the postsurgical outcome of 6 patients to the dipole localization and the resection margins. In all 6 patients in whom the dipole, and hence the estimated seizure generator, was removed the surgical outcome was favorable. We conclude that the inverse solution algorithm is a promising method for using the scalp EEG to localize the sources of electrical activity in the human brain in routine clinical electroencephalography and provides three-dimensional data not available from conventional analysis.