The individual variability of the dentato-rubro-thalamic tract in the planning of stereotactic operations in patients with tremor

Abstract

Background. Stereotactic operations on the ventral‑intermediate nucleus of the thalamus (Vim) and the posterior subthalamic area (PSA) are used for the surgical treatment of tremor. Since these structures are invisible in standard magnetic resonance imaging (MRI) regimes, indirect stereotactic guidance is mainly used during operations. MRI tractography allows taking into account the individual variability of the target structures for tremor, visualizing the target directly, but this technique has not yet entered the routine practice of preparing operations.Aim. The aim of the work is to study the variability of the position of the dentato‑rubro‑thalamic tract (DRT), determined according to MRI tractography data, in relation to the main reference points for indirect stereotactic guidance, as well as to the visible landmarks on MRI in FGATIR mode, to assess the validity of the currently used methods of preparing operations in patients with tremor.Materials and methods. Probabilistic MRI tractography of DRT based on the HARDY protocol was performed in 34 patients. Additionally, 3D T1 tomograms were obtained with axial slices with an isotropic voxel size equal to 1 mm, as well as FLAIR sagittal slices with a thickness of 1.12 and a pitch of 0.56 mm. Eleven patients additionally underwent a series of MRI sections according to the FGATIR program with a thickness of 1 mm, without an intersectional gap.Results. A significant variability of the DRT position has been established both in the coordinate system of the anterior and posterior commissures, and in relation to standard targets for indirect stereotactic guidance. In addition, a visible interhemispheric asymmetry of the position of the tracts was revealed. The smallest degree of deviation from the tract was noted for the trajectories of deep brain stimulation electrodes implanted in the caudal zona incerta (cZI) at the level of the maximum diameter of the red nuclei. A high degree of correspondence between the tract and the target zone of prelemniscal radiations (Raprl) was also established on tomograms in the FGATIR mode.Conclusions. The standard target points for the indirect targeting of Vim targets and the cerebello‑thalamic tract in PSA give a deviation of more than 2 mm from DRT in almost half of patients. During the use of cZI as a standard target for indirect guidance in the treatment of tremor, the DRT is located at the zone of stereotactic impact at the level of the 2nd or 3rd contact of the electrode in 76.5 % of cases. FGATIR mode allows visualizing the structure of Raprl, with stereotactic guidance on which the effect on the DRT can be achieved in 86.4 % of cases.