Invasive Investigation of Insular Cortex Epilepsy
Invasive long-term EEG investigations of the insula have been performed since the mid-nineties in an expanding range of focal epilepsies suspected to involve the insular cortex. The various clinical forms of insular epilepsies were delineated during the last 2 decades, and include the following presentations: perisylvian epilepsy, temporal plus epilepsy, sleep hypermotor epilepsy, MRI-negative frontal and parietal lobe epilepsies, and insular lesions. In fact, a majority of complex stereoelectroencephalography procedures will include at least one electrode targeting the insula. Stereoelectroencephalography is currently the preferred method to investigate the insula, using orthogonal, oblique, or a combination of both trajectories, with no evidence of higher risk of intracranial bleeding than in other brain regions. Orthogonal trajectories allow to sample the overlaying opercula, while oblique trajectories offer a better sampling of the insular cortex. Intrainsular ictal EEG pattern are often characterized by a prolonged focal discharge restricted to one of the five insular gyri, militating for a dense enough sampling of the insular cortex in suspected insular epilepsies. Stereoelectroencephalography offers the potential to perform thermolesion of insular epileptogenic zones which, together with MRI-guided laser ablation, represent a possibly safer alternative treatment to open-skull surgical resection of the insula.