Abstracts

RATIONALE: The aim of the study was to assess MEG contribution to presurgical evaluation in patients with focal epilepsies associated with cavernomas.
METHODS: Among 82 operated epilepsy patients with magnetoencephalography (MEG) findings during presurgical evaluation, histological assessment of the removed tissue had revealed cavernomas in eight cases. Three cases are selected to demonstrate the potential complexity of localizing epileptic activity in relationship to such lesions.
MEG was recorded with a 74 channel dual unit biomagnetometer (Magnes II, 4D-Neuroimaging). Co-registered magnetic tomography resonance (MRT) data were available for all patients. Standard procedures of epileptic spike localizations were based upon the model of an equivalent current dipole in a homogeneously conducting sphere. In two cases, additional current density reconstructions were carried out, and realistically shaped head models were computed, according to the boundary element method (BEM).
RESULTS: 1. In the first patient, MEG spike localization revealed a circumscribed center of epileptic activity at the very border of the lesion. The subsequent resection resulted in abolition of seizures.
2. Two lesions were found in the second case, one in the frontal lobe, the other one in the temporal lobe. MEG spike localizations clearly indicated epileptogenicity of the temporal lobe. The patient markedly benefited from removal of the temporal lesion.
3. The third patient had a poor outcome after resection of a cavernoma in the basal region of the left temporal lobe. Postoperative MEG spike analysis yielded localizations in the dorsal part of the temporal lobe, distant from the resection cavity. Fractionated stereotactic radiotherapy of this site significantly reduced seizure frequency.
CONCLUSIONS: The results illustrate the worthwhile contribution of MEG in presurgical epilepsy evaluation in symptomatic epilepsy with lesional etiology.
[Supported by: Deutsche Forschungsgemeinschaft (DFG), STE 380/9 - 1]