Neuromagnetic localization of spike sources in perilesional, contralateral mirror, and ipsilateral remote areas in patients with cavernoma

Purpose: To assess neuromagnetic spike localization as an indication for extended lesionectomy of cavernoma. Methods: Electroencephalography (EEG) and magnetoencephalography (MEG) was simultaneously recorded in 17 patients (8 men, mean age 29.7 years) with single cavernoma. The location of the equivalent current dipole (ECD) of the interictal spikes was correlated with the lesion shown by magnetic resonance imaging. Results: Preoperative ECD localization was classified into four types: perilesional, adjacent to the cavernoma only (n = 6); mirror, adjacent to the lesion and at the contralateral homologous site (n = 5); remote, mainly at a remote site in the ipsilateral hemisphere (n = 3); and no spikes (n = 3). The spikes were detected by only MEG in two of five "mirror" and all three "remote" patients. In the mirror group, contralateral spikes were synchronized with the ipsilateral spikes, or also occurred independently. Two "perilesional" and two "mirror" patients became seizure-free and spike-free after extended lesionectomy. In contrast, the other two "mirror" patients had residual seizures and spikes after pure lesionectomy. Conclusion: The detectability of mirror and remote spikes was higher by MEG than by EEG, whereas the detectability of perilesional spikes was similar by MEG and EEG. Therefore, the use of both EEG and MEG will provide the maximum information about spike distribution and propagation. Residual seizures and spikes after pure lesionectomy, but not after extended lesionectomy, in the "mirror" patients suggest the importance of resection of the perilesional irritable zone. Extended resection of the irritable cortex surrounding cavernoma is recommended for better seizure control, particularly in "mirror" patients.