The Utility of Dipole Source Analysis of Seizure Onsets in the Localization of Epileptogenic Zones as Assessed by Postsurgical Outcome

T.B.J. Wiederin; K.H. Chiappa; T. Krings; B.N. Cuffin; D.B. Hoch; A.J. Cole; G.R. Cosgrove

Published: 23 August 1999

In 20 patients (90 seizures) with an Engel class-I surgical outcome, we assessed the ability of preoperative dipole source analysis of ictal-onset EEG activity to predict postoperative outcomes. The patients had pharmacologically intractable epilepsy due to lesions of diverse etiologies and their scalp EEGs showed rhythmic theta activity or repetitive spiking at seizure onset. All patients were seizure free postoperatively (mean 18 months, range 3­36). The equivalent dipoles, calculated using a four-shell spherical head model and a single moving-dipole inverse-solution algorithm, were plotted on the patients' postoperative MRIs and the locations were assessed relative to the resection margins. In 14 of the 20 patients, no dipole was located within the resection margins; in 4 patients the majority of the dipoles were located outside the resection margins; and in 2 patients all of the dipoles were resected. No consistent displacement of the dipoles relative to the resections, which might have suggested propagation patterns, was evident, nor was there a consistent migration of the dipole location from the first to the second or from the first to the third segments of the seizure onsets. We conclude that the inverse-solution algorithm as implemented in this study is not useful for localizing seizure onsets or propagation patterns in the epileptic human brain.

Keywords: dipole source, seizure onset, outcome