Targeting the posterior subthalamic area for essential tremor: proposal for MRI-based anatomical landmarks

Abstract

OBJECTIVEDeep brain stimulation (DBS) of the posterior subthalamic area (PSA) is an alternative to thalamic DBS for the treatment of essential tremor (ET). The dentato-rubro-thalamic tract (DRTT) has recently been proposed as the anatomical substrate underlying effective stimulation. For clinical purposes, depiction of the DRTT mainly depends on diffusion tensor imaging (DTI)–based tractography, which has some drawbacks. The objective of this study was to present an accurate targeting strategy for DBS of the PSA based on anatomical landmarks visible on MRI and to evaluate clinical effectiveness.METHODSThe authors performed a retrospective cohort study of a prospective series of 11 ET patients undergoing bilateral DBS of the PSA. The subthalamic nucleus and red nucleus served as anatomical landmarks to define the target point within the adjacent PSA on 3-T T2-weighted MRI. Stimulating contact (SC) positions with reference to the midcommissural point were analyzed and projected onto the stereotactic atlas of Morel. Postoperative outcome assessment after 6 and 12 months was based on change in Tremor Rating Scale (TRS) scores.RESULTSActual target position corresponded to the intended target based on anatomical landmarks depicted on MRI. The total TRS score was reduced (improved) from 47.2 ± 15.7 to 21.3 ± 10.7 (p < 0.001). No severe complication occurred. The mean SC position projected onto the PSA at the margin of the cerebellothalamic fascicle and the zona incerta.CONCLUSIONSTargeting of the PSA based on anatomical landmarks representable on MRI is reliable and leads to accurate lead placement as well as good long-term clinical outcome.

Structure-function relationship of the posterior subthalamic area with directional deep brain stimulation for essential tremor

“…A preoperative high-resolution stereotactic CT scan was performed with the stereotactic frame in place (Leksell, Elekta). The target was defined visually on T2-weighted axial slices based on anatomical landmarks as described previously by our group ( Nowacki et al, 2018a ). Surgery was performed with the patient awake under local anesthesia with microelectrode guidance and intraoperative clinical testing.…”

“…In cases of severe tremor despite optimized medical treatment, deep brain stimulation is an effective and safe alternative ( Limousin et al, 1999 , Lozano, 2000 ). The ventral intermediate nucleus (VIM) of the thalamus is the classical and widely accepted target for DBS ( Benabid et al, 1991 , Sammartino et al, 2016 , Nowacki et al, 2018a ). Alternatively, previous work has evaluated the efficacy of DBS in regions ventral to the thalamus that have been referred to as the zona incerta, the prelemniscal radiations, the posterior subthalamic area and the dentato-rubro-thalamic-tract by different groups ( Carrillo-Ruiz et al, 2008 , Blomstedt et al, 2010 ).…”

Deep-Brain Stimulation for Essential Tremor and Other Tremor Syndromes: A Narrative Review of Current Targets and Clinical Outcomes

“…Together, these findings suggest that PSA DBS (including caudal Zi and Raprl targets) may provide at least equally effective tremor relief than Vim DBS with a similar side-effect profile and possibly more efficient stimulation parameters. A popular stimulation target in this area appears to be 1-2 mm inferior to the AC-PC plane, at the interface between the caudal Zi and Raprl (circle in Figure 2C) [24,51], where fibers in the PSA are the densest, before they progressively fan out as they reach the Vim and then project to cortical areas [16]. While stimulation of both targets likely affect the same network, the PSA's proximity to the medial lemniscus and internal capsule makes it more vulnerable to off-target side-effects, and this may indeed factor into the observed lower energy parameters after programming is complete.…”

Deep Brain Stimulation for Essential Tremor and Other Tremor Syndromes: A Narrative Review of Current Targets and Clinical Outcomes

“…Together, these findings suggest that PSA DBS (including caudal Zi and Raprl targets) may provide at least equally effective tremor relief than Vim DBS with a similar side-effect profile and possibly more efficient stimulation parameters. A popular stimulation target in this area appears to be 1-2 mm inferior to the AC-PC plane, at the interface between the caudal Zi and Raprl (circle in Figure 2C) [24,48], where fibers in the PSA are the densest, before they progressively fan out as they reach the Vim and then project to cortical areas [16]. While stimulation of both targets likely affect the same network, the PSA's proximity to the medial lemniscus and internal capsule makes it more vulnerable to off-target side-effects and this may indeed factor into the observed lower energy parameters after programming is complete.…”