Intracranial monitoring using electroencephalography (IC-EEG) continues to play a critical role in the assessment of patients with medically intractable localization-related epilepsy. There has been minimal change in grid or electrode design in the last 15–20 years, and the surgical approaches for implantation are unchanged. Intracranial monitoring using EEG allows detailed definition of the region of ictal onset and defines the epileptogenic zone, particularly with regard to adjacent potentially eloquent tissue. Recent developments of IC-EEG include the coregistration of functional imaging data such as magnetoencephalography to the frameless navigation systems. Despite significant inherent limitations that are often overlooked, IC-EEG remains the gold standard for localization of the epileptogenic cortex. Intracranial electrodes take a variety of different forms and may be placed either in the subdural (subdural strips and grids, depth electrodes) or extradural spaces (sphenoidal, peg, and epidural electrodes). Each form has its own advantages and shortcomings but extensive subdural implantation of electrodes is most common and is most comprehensively discussed. The indications for intracranial electrodes are reviewed.
Advances in intracranial monitoring
Jeffrey P. Blount, Jason Cormier, Hyunmi Kim, Pongkiat Kankirawatana, Kristen O. Riley, and Robert C. Knowlton
Letter to the Editor. Atypical pituitary adenoma
Lauren E. Rotman, T. Brooks Vaughan, James R. Hackney, and Kristen O. Riley
Modulation of neural oscillations by vagus nerve stimulation in posttraumatic multifocal epilepsy: case report
Adeel Ilyas, Emilia Toth, Diana Pizarro, Kristen O. Riley, and Sandipan Pati
The putative mechanism of vagus nerve stimulation (VNS) for medically refractory epilepsy is desynchronization of hippocampal and thalamocortical circuitry; however, the nature of the dose-response relationship and temporal dynamics is poorly understood. For greater elucidation, a study in a nonepileptic rat model was previously conducted and showed that rapid-cycle (RC) VNS achieved superior desynchrony compared to standard-cycle (SC) VNS. Here, the authors report on the first in-human analysis of the neuromodulatory dose-response effects of VNS in a patient with posttraumatic, independent, bilateral mesial temporal lobe epilepsy refractory to medications and SC-VNS who was referred as a potential candidate for a responsive neurostimulation device. During stereotactic electroencephalography (SEEG) recordings, the VNS device was initially turned off, then changed to SC-VNS and then RC-VNS settings. Spectral analysis revealed a global reduction of power in the theta (4–8 Hz) and alpha (8–15 Hz) bands with both SC- and RC-VNS compared to the stimulation off setting (p < 0.001). Furthermore, in the alpha band, both SC- and RC-VNS were associated with greater global desynchrony compared to the off setting (p < 0.001); and, specifically, in the bilateral epileptogenic hippocampi, RC-VNS further reduced spectral power compared to SC-VNS (p < 0.001). The dose-response and temporal effects suggest that VNS modulates regional and global dynamics differently.
Robot-assisted stereoelectroencephalography exploration of the limbic thalamus in human focal epilepsy: implantation technique and complications in the first 24 patients
Ganne Chaitanya, Andrew K. Romeo, Adeel Ilyas, Auriana Irannejad, Emilia Toth, Galal Elsayed, J. Nicole Bentley, Kristen O. Riley, and Sandipan Pati
Despite numerous imaging studies highlighting the importance of the thalamus in a patient’s surgical prognosis, human electrophysiological studies involving the limbic thalamic nuclei are limited. The objective of this study was to evaluate the safety and accuracy of robot-assisted stereotactic electrode placement in the limbic thalamic nuclei of patients with suspected temporal lobe epilepsy (TLE).
After providing informed consent, 24 adults with drug-resistant, suspected TLE undergoing evaluation with stereoelectroencephalography (SEEG) were enrolled in the prospective study. The trajectory of one electrode planned for clinical sampling of the operculoinsular cortex was modified to extend it to the thalamus, thereby preventing the need for additional electrode placement for research. The anterior nucleus of the thalamus (ANT) (n = 13) and the medial group of thalamic nuclei (MED) (n = 11), including the mediodorsal and centromedian nuclei, were targeted. The postimplantation CT scan was coregistered to the preoperative MR image, and Morel’s thalamic atlas was used to confirm the accuracy of implantation.
Ten (77%) of 13 patients in the ANT group and 10 (91%) of 11 patients in the MED group had electrodes accurately placed in the thalamic nuclei. None of the patients had a thalamic hemorrhage. However, trace asymptomatic hemorrhages at the cortical-level entry site were noted in 20.8% of patients, who did not require additional surgical intervention. SEEG data from all the patients were interpretable and analyzable. The trajectories for the ANT implant differed slightly from those of the MED group at the entry point—i.e., the precentral gyrus in the former and the postcentral gyrus in the latter.
Using judiciously planned robot-assisted SEEG, the authors demonstrate the safety of electrophysiological sampling from various thalamic nuclei for research recordings, presenting a technique that avoids implanting additional depth electrodes or compromising clinical care. With these results, we propose that if patients are fully informed of the risks involved, there are potential benefits of gaining mechanistic insights to seizure genesis, which may help to develop neuromodulation therapies.