Confirmation of two magnetoencephalographic epileptic foci by invasive monitoring from subdural electrodes in an adolescent with right frontocentral epilepsy

Purpose: To report our evaluation of interictal two epileptic spike fields on magnetoencephalography (MEG) by using invasive intracranial monitoring in a patient without lesion on magnetic resonance imaging (MRI). Methods: A 15-year-old left-handed boy with a 9-year history of refractory simple partial seizures, secondarily generalized, and a normal MRI, was studied with MEG to define magnetic spike sources, followed by invasive intracranial monitoring with subdural electrodes to delineate the epileptogenic zone and eloquent function pursuant to focal cortical excision. Results: MEG demonstrated two spike foci on the right middle frontal and inferior rolandic areas adjacent to the sensory area. Ictal recordings during prolonged invasive monitoring from subdural electrodes revealed two epileptogenic zones in the same locations as those defined by MEG. Focal cortical excision was performed of each epileptogenic zone. The patient has been seizure free for 24 months without neurologic deficit. Conclusions: Magnetic source imaging is a valuable adjunct in the planning of subdural grid placement in epilepsy surgery, particularly in patients in whom conventional imaging fails to reveal a lesion.