Abstracts

Rationale: Intracranial monitoring for epilepsy has been proven to enhance diagnostic accuracy and provide localizing information for surgical treatment of intractable seizures. We investigated the usefulness of hippocampal depth electrodes in the era of high resolution imaging techniques.Methods: Between 1988 and 2010, one hundred patients underwent occipitotemporal hippocampal depth electrode (OHDE) implantation as part of arrays for invasive seizure monitoring, and their charts were retrospectively reviewed. Our technique involved the stereotactically-guided (using the Leksell model G frame) implantation of a 12 contact depth electrode directed along the long axis of the hippocampus, through an occipital twist drill hole. Results: From the 100 patients that had intracranial investigation, 84 underwent surgical resection (mean age 35.5, 52.4% males) of the seizure focus. MRI showed mesial temporal lobe sclerosis (MTS) in 27%, was abnormal without MTS in 55% of the patients, and was normal in 18%. One patient developed a small asymptomatic occipital hemorrhage around the electrode tract. The use OHDE enabled resective epilepsy surgery in 34.3% of the patients who eventually underwent complete or selective temporal lobe resection. The hippocampal formation was spared during surgery because of data obtained from the depth electrodes showing no or only secondary involvement in 29.2% of all the patients with preoperative temporal localization. The use of OHDE prevented resections in 8.7% of patients with radiographic MTS. The percentage of patients that underwent resection and had an Engel classification of 1 or 2 post-resection was 72% at 2 of follow up.Conclusions: The use of OHDE in intracranial epilepsy monitoring has a favorable risk profile and in our experience proved to be a valuable component of intracranial investigations since it can provide the sole evidence for resection of some epileptogenic foci and also result in hippocampal sparing or prevent resections in other patients.