The role of tractography in the localization of the Vim nucleus of the thalamus and the dentato-rubro-thalamic tract for the treatment of tremor.

The ventralis intermedius (Vim) nucleus of the thalamus is the usual surgical target for tremor. However, locating the structure may be difficult as it is not visible with conventional imaging methods; therefore, surgical procedures typically use indirect calculations correlated with clinical and intraoperative neurophysiological findings. Current ablative surgical procedures such as Gamma-Knife thalamotomy and magnetic resonance-guided focused ultrasound require new alternatives for locating the Vim nucleus. In this review, we compare Vim nucleus location for the treatment of tremor using stereotactic procedures versus direct location by means of tractography. The most widely used cytoarchitectonic definition of the Vim nucleus is that established by Schaltenbrand and Wahren. There is a well-defined limit between the motor and the sensory thalamus; Vim neurons respond to passive joint movements and are synchronous with peripheral tremor. The most frequently used stereotactic coordinates for the Vim nucleus are based on indirect calculations referencing the mid-commissural line and third ventricle, which vary between patients. Recent studies suggest that the dentato-rubro-thalamic tract is an optimal target for controlling tremor, citing a clinical improvement; however, this has not yet been corroborated. Visualisation of the cerebello-rubro-thalamic pathway by tractography may help in locating the Vim nucleus. The technique has several limitations, and the method requires standardisation to obtain more precise results. The utility of direct targeting by tractography over indirect targeting for patients with tremor remains to be demonstrated in the long-term.