Direct identification of ventrointermediate nucleus of the thalamus on magnetic resonance and computed tomography images.

The ventro-intermediate (Vim) nucleus of the thalamus is a commonly used target for the treatment of tremor. The thalamic fasciculus contains myelinated fibers, believed to play a role in the generation of tremor, that converge into a dense bundle at the inferior aspect of the Vim nucleus, making it visible on magnetic resonance (MR) and computed tomography (CT) images. This structure, therefore, can be visualized directly and targeted for thalamotomy. Thalamotomies were performed on nine patients (who have a follow-up of 13-23 months) with parkinsonian and essential tremors using MR and CT images. The tremor target was hypointense on MR images obtained in inversion recovery sequence and hypointense on CT images. It was therefore visualized, directly targeted, and probed. Stimulation studies were done to physiologically confirm accuracy of the probe placement and then a radiofrequency lesion was made. Stimulation of the target identified as the Vim nucleus on MR and CT images produced responses similar to those expected from the Vim nucleus. After this site was lesioned tremor disappeared in all nine patients. The Vim nucleus of the thalamus is visible on MR and CT images. Destruction of this target abolishes parkinsonian and essential tremors.