Prelemniscal Radiations: A New Reliable Landmark of the Thalamic Nucleus Ventralis Intermedius Location

The thalamic nucleus ventralis intermedius (Vim nucleus) is the main surgical target for the management of intractable tremor. The Vim nucleus cannot be reliably located with routine stereotactic imaging, and so targeting relies on indirect coordinates.

We propose to investigate if colored fractional anisotropy (FA) mapping can help to locate the Vim nucleus by identifying its borders, particularly the prelemniscal radiations (Raprl) that lie below and behind the nucleus.

We retrospectively reviewed the colored FA maps for 18 consecutive patients having undergone gamma knife stereotactic Vim thalamotomy for disabling tremor.

The Raprl were easily located on colored FA maps and enabled the identification of the lower and posterior borders of the Vim nucleus in all patients. In the medial plane, the mean distance ± SD between the Raprl and Vim nucleus was 0.77 ± 1.19 mm (range: 0.1-3.3). The Raprl were located 1.35 ± 1.33 mm (range: 0.2-3.9) behind the Vim nucleus and 1.99 ± 1.23 mm (range: 0.7-4.4) below it. The mean vector distance ± SD between the Vim nucleus and the Raprl was 3 ± 1.38 mm (range: 1.25-5.2).

The Raprl can be easily seen on colored FA maps and constitute a reliable landmark for the borders of the Vim nucleus.