3-DIMENSIONAL LOCALIZATION OF SUBCLINICAL ICTAL ACTIVITY BY MAGNETOENCEPHALOGRAPHY - CORRELATION WITH INVASIVE MONITORING

BACKGROUND Although magnetoencephalography (MEG) provides accurate inf ormation on the spatial distribution and temporal patterns of the ''in terictal'' epileptic activities, it is interictal in nature and theref ore also prone to all the problems associated with interictal data. ME THODS We investigated the subclinical ''ictal'' epileptic activity wit h a 37-channel, large-array biomagnetometer and mapped the data onto a three-dimensional image in a patient with intractable frontal lobe ep ilepsy. Dipole source localization was calculated based on magnetic fi elds for both the interictal and subclinical ictal activities, RESULTS The current dipoles of the interictal MEG spikes (MEG irritative zone ) were revealed to be scattered in the left anterior frontal lobe, whe reas that of the subclinical ictal onset (MEG subclinical ictal onset zone) was surrounded by the interictal dipole cluster. The dipole sour ce localization of the propagating activities was not calculated with a single dipole model. The MEG subclinical ictal onset zone correlated well with the ictal onset zone subsequently recorded by invasive subd ural electrophysiological monitoring. After multiple subpial transecti on of the deduced epileptogenic area, a dramatic reduction of the seiz ures occurred. CONCLUSION These results illustrate the potential of ME G for localizing the epileptogenic foci with high spatial and temporal resolution. (C) 1998 by Elsevier Science Inc.