Abstracts

Rationale: Stereo-electroencephalography (SEEG) is designed to target distributed cortical networks responsible for the electro-clinical seizure syndrome and enable localization of the site of seizure onset in patients with intractable epilepsy. When the pre-implantation hypothesis invokes bilateral mesial frontal lobes it requires sampling of several deep-seated cortical sites in both hemispheres. In this study we demonstrate the feasibility of sampling bi-hemispheric areas with an intentional implantation of SEEG electrodes crossing midline (SECM) sampling cortex on both sides of the interhemispheric fissure._x000D_
Methods: An analysis of 231 consecutive SEEG procedures over 8 years were used to identify instances of bi-hemispheric sampling using the trans-midline SEEG technique._x000D_
Results: In fifty-three SEEG cases, a total of 126 electrodes, crossed the interhemispheric fissure all in the frontal lobes, with an average of 2.4 per patient. Eighty-three targeted the cingulate gyrus (18 rostral, 43 anterior and 22 middle), thirty-one targeted the posterior orbitofrontal region, eight sampled the medial prefrontal cortex and 4 targeted nodular heterotopias (PVNH) around the frontal horns. These electrodes originated from the left in 14 patients, right in 16 and 23 from both sides. No hemorrhagic or infectious complications were noted in any of these cases. The driving hypotheses included temporal plus with suspected contralateral involvement in 12 cases, 9 bitemporal, 10 unilateral frontal, 5 bifrontal o mesial frontal, 12 with frontal vs temporal involvement, 3 frontocentral or frontoparietal and 2 temporoparietal. In most of the patients (44) the implantation scheme was bilateral and in 9 unilateral. In 37 patients, the epileptic zone resulted to be focal (19 temporal, 13 frontal, 2 parietal, 1 temporoparietal and 2 PVNH), 9 bitemporal, 3 multifocal, 1 bihemispheric and in 3 nonconclusive (Table 1).  Consequently, most of the patients underwent either resection (26) or laser ablation (5) or of both (3), with a few needing neuromodulation alone (11) or in combination with resection and/or ablation (5). The ictal onset zone was localized to the frontal lobe in 16 cases, in these the SECM isolated interictal and ictal activity in the contralateral hemisphere in 6 cases and independent bihemispheric seizure activity in 2 cases._x000D_  _x000D_ Conclusions: Based on this extensive experience of bi-hemispheric sampling, we conclude that this technique is safe and effective, with an approximate yield of a single electrode of 15% in this series. SECM may reduce the number of electrodes used to sample bilateral mesial frontal or orbitofrontal cortices, and such an approach may lower risks of hemorrhage and costs._x000D_
Funding: Not applicable