Objective: To characterize the connectivity of prelemniscal radiations (Raprl) and to identify differences in the fiber populations within the Raprl.

Background: The Raprl have been proposed as a neurosurgical target for the treatment of Parkinson’s disease (PD) since 1970’s, although the anatomic connectivity of this subthalamic area remains unknown. Recent MRI tractography analysis using spherical deconvolution informed filtering of tractograms (SIFT2) provides biologically accurate measures of fiber density.

Methods: Images from 11 healthy subjects and 11 PD patients were acquired using a 3T scanner. Diffusion-weighted images (DWI) were acquired using 120 unique diffusion-gradient directions with b=2000s/mm2 in addition to T1 and T2 volumes. An average response function per group was obtained to perform constrained spherical deconvolution (CSD). Anatomically-constrained tractography was performed followed of track-density images (TDI) with 10 million tracks seeded homogeneously throughout the white matter using MRtrix3 (github.com/MRtrix3). One million streamlines were generated for each ROI (Raprl area manually delineated in each hemisphere) and SIFT2 was applied. Tracts were virtually dissected according to cortical frontal areas, basal ganglia and cerebellum defined automatically by the co-registration of subject-specific labels according to the Desikan-Killiany Atlas as provided by Freesurfer (v.5.3). Differences of fiber density interconnecting the Raprl to each target between groups were assessed by Student’s t-test.

Results: CSD allowed the determination of the orientation of fiber tracts in the Raprl. Probabilistic tractography showed connectivity with orbitofrontal cortex (OFC), motor and premotor cortex, thalamus, globus pallidus, cerebellum and dorsal brainstem. There were significance differences of fiber density in right hemisphere pathways linking Raprl with lateral OFC cortex (p=0.026) and pars orbitalis (p=0.050).

Conclusions: Raprl could be adequately segmented with 3T MRI using high-resolution anatomical images and TDI which could be useful for neurosurgery planning. Probabilistic tractography based on CSD allows the characterization of Raprl. Tractography may allow the identification of eloquent white matter tracts, and hence provide a better method to plan the approach to surgical targets.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/characterization-and-quantitative-analysis-of-prelemniscal-radiations-in-parkinsons-disease/