Intraoperative ECoG in bottom-of-the-sulcus syndrome using a novel flexible strip electrode

The recording of epileptiform discharges from bottom-of-sulcus focal cortical dysplasia (BOSD) is often difficult during intraoperative electrocorticography (ECoG) due to the deep localization. We describe the use in this scenario of a new-generation electrode strip with high flexibility, easily adapted to cortical gyri and sulci. A right-handed 20-year-old male with drug-resistant focal epilepsy due to BOSD of the inferior frontal gyrus and daily focal aware seizures was evaluated for epilepsy surgery. Based on electroclinical and neuroimaging results, a focal cortectomy guided by ECoG was proposed. ECoG recordings were performed with new-generation cortical strips (Wise Cortical Strip; WCS®) and standard cortical strips. ECoG, performed on the convexity of the frontal cortical surface, recorded only sporadic spikes with both types of strips. Then, after microsurgical trans-sulcal dissection, WCS was molded along the sulcal surface of the suspected BOSD based on 3D-imaging reconstruction, showing continuous/subcontinuous 3-4-Hz rhythmic spike activity from the deepest electrode. Registration after resection of the BOSD did not show any epileptiform activity. Pathology showed dysmorphic neurons and gliosis. No surgical complications occurred. The patient is seizure-free after 12 months. This single case experience shows that highly flexible electrode strips with adaptability to cortical gyrations can identify IEDs originating from deep location and could therefore be useful in cases of bottom of the sulcus dysplasia.