Abstracts

Rationale: Refractory epilepsy is a relatively common problem, affecting about 12% of the population. Surgical treatment is recommended for patients with a seizure focus located in a non-eloquent cortex. However, if functional cortex such as language or motor areas are involved, the treatment options are very limited. Multiple subpial transections (MST) is another option for these patients. However, this technique is not widely used. A systematic review found modest efficacy (24% seizure freedom) and close to 7% permanent deficits. We need better treatment options for patients with focal epilepsy involving eloquent cortex. Methods: We developed the Ictal Network Transection (INT) protocol to treat patients with refractory epilepsy involving eloquent cortex. Presurgical evaluation, as determined by the epileptologist, included scalp video EEG monitoring, EEG source imaging, 3T MRI, ictal SPECT, brain PET, and/or Wada test. Subdural recording of video EEG is performed to confirm localization of interictal and ictal zones. Functional mapping is performed with a traditional bipolar stimulation with an average current of 5 mAmp, and 100Hz stimulation for 5 seconds.The procedure: Electrocorticography is performed intraoperatively to delineate epileptic zones over the eloquent cerebral cortex. Once defined, the cortical sulcus is minutely coagulated over a central relatively avascular zone. The pia is incised with the tip of an 11 blade. Four crossed radial subpial incisions are made to a depth of approximately 5mm using a Rhoton #9 microhook. Care to be taken to avoid injuring any blood vessels, especially at the sulcus. The treated cortical surface is covered with a thin layer of Surgicel. The distance between treatment zones is approximately 1 cm (see picture 1). This procedure is limited to the epileptic cortex at the surface of the surgical field. Electrocorticography is then repeated to assess for frequency, amplitude, and synchronicity of the epileptic discharges. Epileptic non-eloquent areas may be resected along with the above procedure as needed. Results: Eight patients with refractory epilepsy involving eloquent cortex were treated according to our INT protocol. Three out of four patients with evidence of ictal zone around the Wernicke’s area became seizure free after surgery without clinical evidence of language deficit. Language improved in one patient after the procedure. Three patients had ictal zones involving the motor cortex. The severity of seizures improved by restricting local propagation in all of them. One pediatric patient became seizure free and improved autistic symptoms with the development of new language skills. No permanent deficits were observed after the procedure. No evidence of worsening of seizures after one year in four patients. (See Table 1) Conclusions: Ictal Network Transection may safely and effectively improve seizure severity and frequency in patients with intractable focal epilepsy involving eloquent cortex. The main limitation of this procedure is the restriction to the visible brain surface, leaving deep cortical areas untreated. Larger and controlled studies are needed. Funding: No funding