Intraoperative ECoG during MRI-guided laser-interstitial thermal therapy for intractable epilepsy

MRI-guided laser-interstitial thermal therapy is a new modality for epilepsy surgery. In patients with intractable localization-related seizures, it has been used to ablate epileptogenic lesions with less morbidity than conventional craniotomies, and with potentially similar rates of seizure freedom. It is gaining favor in the treatment of mesial temporal sclerosis, in which the circumscribed epileptic focus is amenable to a stereotactic approach. In some centers, intraoperative electrocorticography (ECoG) is a standard procedure during tailored temporal lobectomies that include resection of mesial temporal structures. Results of intraoperative ECoG have been used to guide the extent of resection of mesial temporal structures and for prognostication. Given the limitations of burr-hole access during laser-interstitial thermal therapy, ECoG has not previously been applied. We present two case reports involving intraoperative ECoG monitoring with a depth electrode placed into the parahippocampal region, with recording before and immediately after thermal ablation of the mesial temporal region. In each case, there were decreases in the mesial temporal spike activity after laser ablation of the hippocampus. This is the first demonstration of intraoperative neurophysiologic motoring during laser-interstitial thermal therapy. The role of intraoperative ECoG for guiding the extent of ablation and determining prognosis during MRI-guided laser-interstitial thermal therapy remains to be determined.