Estimation of the Epileptic Focus in Temporal Lobe Epilepsy‐ Investigation with Dipole Tracing Using a Realistic Three‐Shell Head Model

Abstract

Purpose: The location of the electrical generator in the brain can be estimated with dipole tracing. We estimated the equivalent current dipole with scalp electroencephalogram (EEG) in patients with temporal lobe epilepsy by using dipole tracing, and compared the results with the epileptogenic focus identified by long‐term subdural EEG recording. Methods: We studied five patients with temporal lobe epilepsy who underwent long‐term subdural EEG recording. Three were male and two were female patients. Their ages ranged from 18 to 65 years (mean age, 43 years). All patients had intractable seizures and were scheduled to be treated surgically. We recorded the scalp EEG with a digital EEG recorder, and then made three‐shell head models from the computed tomograms. We estimated the equivalent current dipoles with spikes and compared the results with the epileptogenic foci, which were identified with long‐term subdural EEG recording. Results: Case 1 was a 67‐year‐old man. We estimated the equivalent current dipole in the right lateral temporal lobe with dipole tracing. The epileptogenic focus was identified with long‐term subdural EEG recording in the same region. The distance was 18 mm between the equivalent current dipole estimated with dipole tracing and the epileptogenic focus identified with long‐term subdural EEG recording. Case 2 was a 37‐year‐old man. We estimated the equivalent current dipole in the left temporal base and identified the epileptogenic focus with long‐term subdural EEG recording in the same region. The distance was 13 mm between the equivalent current dipole and the epileptogenic focus. Case 3 was a 57‐year‐old woman. We estimated the equivalent current dipole in the left temporal base and identified the epileptogenic focus with long‐term subdural EEG recording in the same region. The distance was 12 mm between the equivalent current dipole and the epileptogenic focus. Case 4 was an 18–year‐old man. We estimated the equivalent current dipole in the left temporal base and identified the epileptogenic foci in the same region. The distance was 19 mm between the equivalent current dipole and the epileptogenic focus. Case 5 was a 38‐year‐old woman. We estimated the equivalent current dipole and identified the epileptogenic focus in the same region. The distance was 8 mm between the equivalent current dipole and the epileptogenic foci. The mean distance in all cases between the equivalent current dipole and the epileptogenic foci was 14 mm. Conclusions: The equivalent current dipole estimated by using dipole tracing of the realistic three‐shell head model with spikes from the scalp EEG was in accordance with the epileptogenic focus identified with long‐term EEG from a subdural grid. There is a close relation between the equivalent current dipole estimated by dipole tracing with spikes and the epileptogenic focus identified with subdural EEG recording.