Abstracts

Hippocampal depth electrodes are useful in lateralizing and localizing medial temporal lobe seizures. Historically these have been placed either orthogonally or transversely using frame based or frameless stereotaxy. This method can provide quality electrical recordings of hippocampal activity, but is a blind procedure with inherent risks and limitations including bleeding, hippocampal injury, inconsistent hippocampal orientation, and incomplete sampling. We report the placement of ventricular depth electrodes under framless stereotactic and neuro-endoscopic guidance using direct visualization to assure safe and consistent placement of hippocampal recording electrodes, with quality recordings leading to successful seizure localization., Frameless stereotactic navigation (Steath Treon Plus, Medtronic) was used to guide occipito-parietal burr hole placement and endoscope trajectory. A neuro-endoscope (Channel[trade] Neuroendoscope, Medtronic) was placed into the atria of the lateral ventricle, then guided down the temporal horn under direct visualization. A 10 contact, 5 mm spacing depth electrode (Ad-tech, Racine WI) was passed through the endoscope with 1 - 2 contacts placed into the temporal pole. The endoscope was then removed using flouroscopy to verify stable electrode position. Electrode position was verified by co-registration of post-operative CT scan to pre-operative MRI in all patients., Eleven ventricular electrodes were placed in 6 patients undergoing surgery for intracranial localization of partial seizures. Successful navigation of the temporal horn was achieved in all patients, and electrodes were verified to be touching the hippocampus in all patients visually and by post-operative imaging. No infection, neurologic injury, or post-operative hemorrhage was seen. Quality recordings were obtained from all electrodes, and seizure onsets were documented in 7/11 electrodes, with reversal potentials seen along the hippocampus using a bipolar montage. Two patients underwent anteromedial temporal resection 6 weeks post-implantation, with pathology showing gliosis adjacent to the electrode location., Electrocorticography may be performed using depth electrodes placed in the temporal horn of the lateral ventricle. Placement of temporal horn electrodes under direct neuro-endoscopic visualization can be performed safely, and provide high quality recordings of hippocampal activity without significant injury to the structure. Temporal horn electrodes are situated in a predictable anatomical relationship to hippocampal structures for reproducible recordings from the same hippocampal subfields between patients. Neuro-endoscopically placed ventricular electrodes may offer a safe and effective alternative to orthogonal and longitudinal hippocampal electrodes for localization of medial temporal lobe seizures.,