Beamforming of ictal MEG aiding subtle focal cortical dysplasia localization

A case is presented of a 17-year-old right-handed male with drug-resistant epilepsy (DRE), initially presenting with non-lesional MRI findings, where ictal MEG beamforming successfully localized a subtle Focal Cortical Dysplasia (FCD). His seizure onset began at age 13, with episodes evolving into bilateral tonic-clonic seizures. Despite various medication trials and normal initial electroencephalograms, his seizures escalated in frequency and severity by age 16. Subsequent diagnostics were unable to reveal definitive lesions, including a high-resolution MRI and various functional imaging techniques. MEG was performed, capturing two electroclinical seizures but without interictal epileptiform discharges. Frequency-based beamforming analysis localized the seizure onset to the right anterior precuneus and superior parietal lobule. This result prompted a re-evaluation of the same MRI images, revealing subtle cortical abnormalities and pinpointing an FCD. Subsequent stereoelectroencephalography confirmed these findings, and the patient underwent successful Laser Interstitial Thermal Therapy, resulting in seizure freedom. This case highlights the utility of frequency-based ictal MEG beamforming in identifying epileptogenic zones and its potential as a powerful tool in the presurgical assessment of DRE patients and non-invasive identification of subtle FCD, especially when traditional methods are unable to localize.