Abstracts

Rationale: There has been growing interest in thalamic sampling during stereotactic electroencephalography (sEEG). Data on thalamic sEEG safety and accuracy is scarce. Here, we report on the safety and accuracy of thalamic sEEG and compare sEEG outcomes and thalamocortical connectivity to thalamic DBS for epilepsy from a single center.

Methods: This study included all patients with epilepsy implanted with thalamic sEEG or DBS between 2018-2024. Electrode contact proximity to Morel thalamic atlas structures (anterior nucleus of the thalamus (ANT), centromedian nucleus (CM) or pulvinar (PUL)) were performed using an open-source package. sEEG surgery used a precision aiming device, 3D printed stereotactic guide, or robotic system; DBS surgery used a rigid frame and to-target cannula. Acute complications were identified by postoperative imaging and chart review.
Volume of tissue engagement was calculated from the contact with minimum proximity value to target, then mirrored to the left-hemisphere. Weighted centers of mass were calculated for each target and electrode type using volumes from select patients. Fibers were seeded from 4-voxel radius spheres around each center using a structural normative connectome of healthy subjects.

Results: A total of 162 sEEG electrodes (126 ANT, 27 CM, 9 PUL) were implanted in 111 patients (Fig 1), with median proximity of 0.32 mm [IQR=0.24-1.06], 0.26 mm [IQR=0.20-0.40], and 0.15 mm [IQR=0.12-0.18], respectively. A total of 189 DBS electrodes (141 ANT, 35 CM, 13 PUL) were implanted in 83 patients, with median proximity of 0.24 mm [IQR=0.17-0.33], 0.22 mm [IQR=0.16-0.28], and 0.21 mm [IQR=0.16-0.23], respectively. Target-specific accuracy comparison showed minimally greater proximity in ANT sEEG (0.08 mm, p=5.1e-6) and PUL DBS (0.06 mm, p=0.038) subgroups, with no significant difference in CM subgroups (p=0.059) (Fig 2).
In ANT sEEG subgroup, there were 8 outliers defined as proximity value >3 mm, whereas 1 patient was identified as an outlier in ANT DBS subgroup. There were no outliers in CM or PUL subgroup in either sEEG or DBS cohort. No significant difference in accuracy was seen in pediatric vs adult (p=0.065) and single vs multitarget sEEG cases (p=0.25).
For sEEG, one patient (0.9%) developed a symptomatic intraparenchymal hemorrhage with transient weakness of the left upper extremity; asymptomatic radiographic complications were noted in 5.4% of patients. For DBS, three patients (3.7%) had transient symptomatic radiographic complications; asymptomatic radiographic complications were noted in 3.6% of patients.
Visual analysis of structural thalamocortical connectivity in each subgroup showed excellent overlap (Fig 1).

Conclusions: Thalamic sEEG demonstrates excellent targeting accuracy and a favorable safety profile. Engagement of thalamocortical network by sEEG and DBS is similar for a given thalamic target. Compared to DBS, the higher rates of thalamic sEEG targeting outliers may reflect differences in stereotactic targeting systems. The smaller cross-sectional area of sEEG vs. DBS leads may contribute to the lower incidence of symptomatic surgical complications with sEEG.

Funding: National Institute of Neurological Disorders and Stroke awards K23NS136792.