The role of magnetoencephalography in the presurgical evaluation of patients with MRI-negative operculo-insular epilepsy

Purpose: Magnetoencephalography (MEG) is considered to be a useful clinical tool to provide additional information for localising the epileptogenic zone or planning intracranial electrode implantation. This study aimed to evaluate the value of MEG in the presurgical localisation of the operculo-insular epileptogenic zone in patients with negative magnetic resonance imaging (MRI). Methods: Thirteen patients with operculo-insular epilepsy and negative MRI who were identified by presurgical evaluation and underwent resective surgery from January 2011 to June 2015 were included and analysed in the study. Results: In presurgical evaluation, the ictal symptoms looked reliable enough to characterise operculo-insular seizures in four patients. MEG spike sources were shown in the operculo-insular region in 11 of 13 (84.6%) patients, including cluster spike sources in 7 patients and scatter spike sources in 4 patients. After MEG examination, the original plan of intracranial electrode implantation was changed in five patients. In these patients, electrodes exploring the operculo-insular cortex were not part of the original plan. The pathological examination showed focal cortical dysplasia (FCD) in 12 patients and FCD with heterotopia in 1 patient. Nine (69.2%)patients were seizure-free in 2-6 years' follow-up. Conclusions: MEG played an additional and valuable role in the localisation of operculo-insular epilepsy for patients with a negative MRI finding.