Abstracts

Rationale: The insular cortex is a complex structure enclosed in the depth of the Sylvian fissure. Covered by highly functional temporal, frontal and parietal opercula, it can generate a variety of ictal symptoms (e.g. viscerosensory, visceromotor, somatosensory, motor, speech and auditory) falsely leading to a diagnosis of temporal, frontal or parietal lobe seizures. Lack or recognition of insular seizures may be responsible for some epilepsy surgery failures. We studied the utility of magnetoencephalography (MEG) in patients with refractory insular epilepsy.Methods: MEG data was reviewed in five patients with refractory insular seizures confirmed by invasive EEG recordings. MEG was performed as part of the noninvasive presurgical evaluation (two patients) or as part of a follow-up assessment of only partially successful insular epilepsy surgery (three patients). MEG data was collected using a 275-channel whole head MEG system for a minimum duration of 30 minutes with simultaneous EEG recording. MEG data was analyzed using a single equivalent current dipole model applied to the earliest peak of each epileptic event. Results: One patient had a tight dipole cluster over the anterior insula and inferior frontal gyrus with uniform orientation. He became seizure free after an anterior insular resection. In the other four patients, spikes appeared more diffusely distributed. Three patients had MEG dipoles that localized to the posterior insula, the temporo parietal junction and the basal temporal area corresponding to posterior insular seizures on intracranial EEG. One patient had anterior insular dipoles, superior temporal gyrus and anterior temporal vertical dipoles corresponding to multifocal perisylvian seizures. MEG insular dipoles were of relatively low amplitude and were associated with either no EEG discharges, positive EEG sharp waves or with low amplitude spikes on EEG. Conclusions: MEG can be useful in the presurgical workup of refractory insular epilepsy particularly if a tight dipole cluster is identified. Insular MEG dipoles can be associated with no EEG spikes or positive sharp waves on scalp EEG.