Optimizing indirect targeting of the centromedian nucleus for deep brain stimulation by incorporating third...

Deep brain stimulation (DBS) of the centromedian nucleus (CM) is used to treat diverse brain diseases including epilepsy, Tourette syndrome, and disorders of consciousness. However, the CM is challenging to visualize on routine MRI. Many surgeons use an indirect targeting method based on established stereotactic coordinates. The authors aimed to quantify how often a DBS electrode's contacts were positioned within the CM using this approach, and to identify alternative indirect coordinates that are more accurate.

Indirect targeting of the CM was performed on 100 MR images obtained in healthy adults, and the resulting coordinates were warped to a common brain template. To estimate positions of DBS contacts along this trajectory, the authors developed a probable electrode location (PEL) mask, modeled on trajectory angles obtained from prior clinical cases. Euclidean and x, y, and z distances between the centroids of the PEL mask and an atlas-based CM mask were measured and defined as error. The percentage of overlaps between the PEL mask and nearby thalamic nuclei was determined. To assess the clinical utility of this methodology, the analysis was validated using 20 MR images obtained in patients with generalized epilepsy, a common clinical indication for CM-DBS.

Using standard indirect coordinates, the authors found the average Euclidean error to be 4.40 ± 1.05 mm, and the x, y, and z errors were 4.19 ± 0.97 mm, 0.73 ± 0.65 mm, and 0.66 ± 0.69 mm, respectively. The PEL mask overlap was 52% with the CM and 65% with the ventral posteromedial nucleus. Variation in third ventricular width was the dominant contributor to these errors (r = -0.71). To overcome this variation, the authors developed alternative indirect coordinates: 4.5 mm lateral to the posterolateral corner of the third ventricle at the level of the posterior commissure. With this refinement, the average Euclidean error was reduced to 1.24 ± 0.5 mm, with 84% of the PEL mask within the CM.

The unavailability of advanced MRI for direct targeting limits access to CM-DBS in resource-constrained neurosurgical programs. Standard indirect coordinates do not provide optimal targeting of the CM, with most contacts laterally placed in the sensory thalamus. The proposed indirect approach may therefore increase the accuracy and availability of CM-DBS, while reducing side effects.