ABSTRACT
Discussion of thalamic surgery for treatment of tremor begins with an understanding of current thalamic anatomical terminology. Several nomenclatures have been used for the nuclei of the motor thalamus (1-4). Hassler’s terminology (1) in the Schaltenbrand atlas (5) is most commonly used in the current movement disorders literature and will be used in this chapter. The motor thalamus lies ventrally and from front to back and consists of the lateral polaris (Lpo), lying most anteriorly, receiving input from the globus pallidus interna (GPi) and the substantia nigra reticulata (SNr); the ventralis oralis anterior (Voa) and the ventral oralis posterior (Vpo) receiving input from the GPi; and the ventral intermediate nucleus (Vim) receiving input from the cerebellum and the lemniscal system (6). The relative contribution of cerebellar and lemniscal input to the Vim is a subject of debate and depends at least in part on whether human clinical or monkey anatomical data are used (6). The ventralis caudalis (Vc) lies posterior to the motor thalamus and receives lemniscal and spinothalamic sensory input. In the Anglo-American nomenclature, the ventral anterior nucleus (VA) includes the Lpo and the Voa, the ventrolateral nucleus (VL) includes the Vop and the Vim, and the ventral posterior nucleus is equivalent to the Vc. Hassler proposed that the Voa was a good target for treatment of rigidity while the Vop was more suitable for treatment of tremor (7).
