Anatomic characterization of prelemniscal radiations by probabilistic tractography: implications in Parkinson’s disease

Abstract

To characterize the anatomical connectivity of the prelemniscal radiations (Raprl), a white matter region within the posterior subthalamic area (PSA) that is an effective neurosurgical target for treating motor symptoms of Parkinson's disease (PD). Diffusion-weighted images were acquired from twelve healthy subjects using a 3T scanner. Constrained spherical deconvolution, a method that allows the distinction of crossing fibers within a voxel, was used to compute track-density images with sufficient resolution to accurately delineate distinct PSA regions and probabilistic tractography of Raprl in both hemispheres. Raprl connectivity was reproducible across all subjects and showed fibers traversing through this region towards primary and supplementary motor cortices, the orbitofrontal cortex, ventrolateral thalamus, and the globus pallidus, cerebellum and dorsal brainstem. All brain regions reached by Raprl fibers are part of motor circuits involved in the pathophysiology of PD; while these fiber systems converge at the level of the PSA, they can be spatially segregated. Fibers of distinct and specific motor control networks are identified within Raprl. The description of this anatomical crossroad suggests that, in the future, tractography could allow deep brain stimulation or lesional therapies in white matter targets according to individual patient's symptoms.

Prelemniscal Lesion for Selective Improvement of Parkinson Disease Tremor

“…On the other hand, with probabilistic tractography, evidenced in our DWI-MRI studies, we have identified a subset of cerebellar-thalamic fibers ending anteriorly over the ventralis oralis posterior nucleus (Vop), as described in other studies [6] (Fig. 1a), overlapping a fiber component connecting Gp with the thalamus [2, 3]. These fibers have been described in anatomical studies as well; arriving at the thalamus in the thalamic fasciculus [7], the fibers connect the Vop with the supplementary motor area and the dorsolateral frontal cortex.…”

“…In previous reports, we described the fiber composition of prelemniscal radiations (Raprl) in Parkinson disease (PD) patients [1, 2] and age- and sex-paired controls [3], evaluated through high-angular-resolution diffusion-weighted imaging (DWI) using magnetic resonance imaging (MRI). In the studied cases, 3 fiber components were identified: cerebellar-thalamic-cortical fibers, globus pallidus (Gp)-pedunculopontine fibers, and frontal orbitofrontal cortex-mesencephalic tegmental fibers.…”

Unilateral Stimulation of Prelemniscal Radiations for the Treatment of Acral Symptoms of Parkinson’s Disease: Long-Term Results

“…We have previously reported that suboptimum outcome results when DBS leads to selective improvement of only one PD symptom. This may be considered as indirect evidence that different symptoms are mediated by different anatomical circuits involving the Raprl .…”

“…The fiber composition of Raprl may explain the effect of DBS on different PD symptoms. Three components have been demonstrated in a cohort of PD patients and control healthy individuals paired in age and sex . The cerebellar‐thalamic cortical component links the cerebellum with the primary motor cortex (PMC) through Vim projections, while a different fiber subset links the supplementary motor area (SMA) through the ventral lateral (Vop) thalamic nucleus; this subset of fibers overlaps the projections of Gpi to the thalamus.…”

“…The third component links the orbitofrontal cortex (OFC) with the mesencephalic tegmentum and had not been previously described in humans, but was recently identified in monkeys through tracers injected in the OFC, traveling in the sub‐thalamus ventral to STN and continuing posteriorly . Being that the OFC is a potent inhibitory structure for behavior and functionally abnormal in PD patients as revealed by neuropsychological testing , it might be related to the pathophysiology of bradykinesia .…”