Brainstem and spinal cord MRI identifies altered sensorimotor pathways post-stroke

Abstract

Damage to the corticospinal tract is widely studied following unilateral subcortical stroke, whereas less is known about changes to other sensorimotor pathways. This may be due to the fact that many studies investigated morphological changes in the brain, where the majority of descending and ascending brain pathways are overlapping, and did not investigate the brainstem where they separate. Moreover, these pathways continue passing through separate regions in the spinal cord. Here, using a high-resolution structural MRI of both the brainstem and the cervical spinal cord, we were able to identify a number of microstructurally altered pathways, in addition to the corticospinal tract, post stroke. Moreover, decreases in ipsi-lesional corticospinal tract integrity and increases in contra-lesional medial reticulospinal tract integrity were correlated with motor impairment severity in individuals with stroke.

Fig. 1

Tracts with white matter integrity changes in brainstem in individuals with stroke compared to controls. a Axial view of the tracts with significant decrease (red-yellow) or increase (blue) in white matter integrity in individuals with stroke compared to controls. Corticospinal tract (CST), corticobulbar tract (CBT), medical reticulospinal tract (MRST), lateral reticulospinal tract (LRST), and medial longitudinal fasciculus (MLF) of the lesioned hemisphere showed significant decreased white matter integrity in individuals with stroke compared to controls. Medial reticulospinal tract (MRST) of non-lesioned hemisphere showed significant increased white matter integrity in individuals with stroke. b Brainstem atlas adapted from Gray’s anatomy and Haines’ neuroanatomy with modification for simplicity, showing the location of tracts. c Sagittal view of the tracts with significant decrease (red-yellow) or increase (blue). (Statistical test: two-sample t test with non-parametric 50,000 permutation. Using the threshold-free cluster enhancement with corrected p < 0.05)

Fig. 2

Tracts with significant correlation between white matter integrity changes and motor impairment. a Axial view of the tract with positive correlation (red-yellow) and negative correlation (blue) between white matter integrity and motor impairment (Fugl–Meyer assessment, FMA) in individuals with stroke. Corticospinal tract (CST) of the lesion hemisphere showed significant positive correlation with impaired motor performance in individuals with stroke. Medial reticulospinal tract (MRST) at the side of non-lesioned hemisphere showed significant negative correlation with impaired motor performance in individuals with stroke. b Sagittal view of the tracts with significant positive (red-yellow) or negative (blue) correlation between white matter integrity and impaired motor performance in individuals with stroke. (Statistical test: within-group voxel-wise correlation analysis, using the threshold-free cluster enhancement and p < 0.05)

Fig. 3

White matter integrity changes in spinal cord of individuals with stroke compared to controls. a Tracts with significant decrease (red-yellow) in white matter integrity (fractional anisotropy (FA)). When compared to controls, individuals with stroke had significant decrease in white matter integrity of lateral corticospinal tract (LCST), cuneate fasciculus (FCu), gracile fasciculus (FGr), and tectospinal tract (TST) of the paretic side. These individuals also showed decreased white matter integrity in medial reticulospinal tract (MRST), medial longitudinal fasciculus (MLF), and medial corticospinal tract (MCST) of non-paretic side, which project ipsilaterally from the lesioned hemisphere. b Tracts with significant increase (blue) in white matter integrity. Medial reticulospinal tract of paretic side, which projects from non-lesioned motor cortices, had significant increased white matter integrity in individuals with stroke compared to controls. (Statistical test: between-group two-sample t test. Voxel-wise p < 0.005 was applied and the cluster-level corrected at p = 0.05.) c High-resolution spinal cord white matter atlas derived from the Gray’s Anatomy Atlas, adapted from ref. . d Correlation of significant white matter integrity changes in individuals with stroke with their motor impairment level. Decreases in lateral corticospinal tract in individuals with stroke had significant positive correlation with their impaired motor performance. Increases in medial reticulospinal tract in individuals with stroke showed a negative correlation with their impaired motor performance. Paretic refers to the side of non-lesioned hemisphere (contralesional). Blue line with abbreviation HC indicates the mean of FA value in healthy controls for lateral corticospinal tract (equal to 0.68) and medial reticulospinal tract (equal to 0.49). Fugl–Meyer Assessment (FMA) score is missing for one participant. Source data are provided as a Source Data file