Robot-assisted stereoelectroencephalography exploration of the limbic thalamus in human focal epilepsy: implantation technique and complications in the first 24 patients

Abstract

<jats:sec><jats:title>OBJECTIVE</jats:title><jats:p>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).</jats:p></jats:sec><jats:sec><jats:title>METHODS</jats:title><jats:p>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.</jats:p></jats:sec><jats:sec><jats:title>RESULTS</jats:title><jats:p>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.</jats:p></jats:sec><jats:sec><jats:title>CONCLUSIONS</jats:title><jats:p>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.</jats:p></jats:sec>

Editorial. Dulling the double-edged sword of human SEEG research

“…For the thalamic electrodes placed by Chaitanya et al, the desired thalamic nucleus was implanted 77%-90% of the time. 2 The imaging, planning, and surgical technique factors contributing to these inaccuracies can now be adjusted and hopefully improved.…”

“…In this issue of Neurosurgical Focus, Chaitanya et al from the University of Alabama at Birmingham (UAB) present their implantation technique and complications in their first 24 patients with suspected temporal lobe epilepsy (TLE) in whom SEEG electrodes were placed to study the limbic thalamus. 2 They show that the research aspect of the procedure is safe, with no symptomatic complications, while providing fundamental knowledge that will likely contribute to thalamic (possibly closed loop) stimulation in the future. In many ways, this research team provides an example of how to carry out SEEG-based human research: out by their referenced early results, the anterior and medial thalamic nuclei provide fertile ground for research into aspects of limbic epilepsy, with excellent prospects for direct patient benefit in the future.…”

“…The surgeon is not part of the research consent process (see Fig. 1, Chaitanya et al 2 ). Surgeon researchers are obviously biased, while patients are known to want to please their surgeons.…”

“…The UAB group found a relatively high rate (21% [n = 5/24]) of asymptomatic bleeding at or just below the electrode entry site. 2 Logically, these bleeds would have been present independent of the research contacts placed into the thalamus. There were no cases of CT-detected thalamic edema or bleeding.…”

Anterior Nucleus of Thalamus Gates Progression of Mesial Temporal Seizures by Modulating Thalamocortical Synchrony

“…Written informed consent was obtained to perform research recordings from the thalamus. Through a meticulous planning and consenting process as detailed previously, adults with drug-resistant suspected TLE were educated that the trajectory of one of the clinical depth electrodes sampling the frontal operculum and insula would be modified to additionally sample the ANT (Chaitanya et al, 2020). This approach would obviate the need for additional electrode placement for research purposes, thereby minimizing the risk of hemorrhage.…”