Parasagittal transinsular electrodes for stereo-EEG in temporal and insular lobe epilepsies

Direct invasive EEG recordings of the insula - due to its particular anatomical position, deeply seated between both opercula - can only be performed with intracerebral electrodes. To date, the technique most commonly used for insular stereoelectroencephalography (SEEG) is the orthogonal-transopercular electrode approach with the Talairach methodology. We propose another technique utilizing MRI with transinsular parasagittal electrodes and a posterior entry point. This avoids passing through the opercula and sylvian vessels running over the insular surface.

Nine patients, whose seizures implicated the insula, underwent brain surgery. Under general anesthesia with a Leksell frame, 3D-T(1) SPGR MRI with gadolinium enhancement was achieved. Surgical planning was performed using the StealthStation with an entry point in the parieto-occipital junction setting the target for the first contact of the lead at the most anterior part of the insula. The trajectory was manipulated in order to have at least 4 contacts per electrode track within the insular cortex. All patients had a postoperative MRI to verify the exact position of each contact.

Insular seizures were recorded in all patients. There was neither intracranial bleeding nor infection. In all of the cases, except 1, the seizures recorded were found to be propagations of the primary epileptic zone located in the temporal lobe, either in the mesial structures or the superior temporal gyrus. Eight patients were operated, 7 with an antero-mesial temporal lobectomy and 1 with dysplasia of the superior temporal gyrus. No insular resections were performed.

We report a novel technique for insular SEEG with parasagittal electrodes, parallel to the insular cortex, with an entry point at the parieto-occipital junction. This technique is based entirely on use of MRI, and avoids passing through the opercula and sylvian vessels.