Intrinsic epileptogenicity of focal cortical dysplasia as revealed by magnetoencephalography and electrocorticography

Focal cortical dysplasia (FCD) is often associated with severe partial epil epsy. In this study, we performed magnetoencephalography (MEG) and electroc orticogrsphy (ECoG) on four patients with FCD-associated epilepsy to confir m the 'intrinsic' epileptogenicity of FCD. In all patients, we determined t he three-dimensional locations of the magnetic sources of the interictal pa roxysmal activities by a single dipole model, and then the estimated dipole localization was superimposed on the magnetic resonance image. The dipole clusters were located in the T2-prolonged lesions, namely in the FCD lesion s themselves. All patients underwent surgery for their medically intractabl e epilepsy, and the acute and/or chronic ECoG were thereafter recorded. Eit her frequent or continuous paroxysmal activities were recorded from the ECo G electrodes which were placed over the surface of the FCD lesion, while fe w paroxysmal activities were observed on the normal appearing adjacent cort ex. Intraoperative depth recordings were performed in a patient with the ne edle electrode inserted into the FCD lesion and they revealed these paroxys mal foci to be located not on the cortical surface but at a depth of 15 mm from the cortical surface where both abnormal giant neurons and bizarre lar ge eosinophilic cells (so-called balloon cells) were also prominently obser ved on the postoperative histological sections. Following a lesionectomy co mbined with the removal of the underlying white matter, three patients demo nstrated a favorable seizure outcome. Our findings thus suggest the FCD les ions to be highly and intrinsically epileptogenic lesions. (C) 1999 Elsevie r Science B.V. All rights reserved.