Neurodegeneration of the Substantia Nigra after Ipsilateral Infarct: MRI R2* Mapping and Relationship to Clinical Outcome

Published Online:https://doi.org/10.1148/radiol.2019182126

High iron content of the substantia nigra remote from supratentorial infarcts was associated with worse long-term motor function after stroke.

Background

The substantia nigra (SN) is suspected to be affected after remote infarction, in view of its large array of connections with the supratentorial brain. Whether secondary involvement of SN worsens overall clinical outcome after a supratentorial stroke has not previously been studied.

Purpose

To assess longitudinal changes in SN R2* by using MRI in the setting of ipsilesional supratentorial infarct and the relationship of SN signal change to clinical outcome.

Materials and Methods

Participants prospectively included from 2012 to 2015 were evaluated at 24–72 hours (baseline visit) and at 1 year with MRI to quantify R2*. The SN was segmented bilaterally to calculate an R2* asymmetry index (SN-AI); greater SN-AI indicated greater relative R2* in the ipsilateral compared with contralateral SN. The 95th percentile of R2* (hereafter, SN-AI95) was compared according to infarct location with mixed linear regression models. We also conducted voxel-based comparisons of R2* and identified individual infarcted voxels associated with high SN-AI95 through voxel-based lesion-symptom mapping. Multivariable regression models tested the association between SN-AI95 and clinical scores.

Results

A total of 181 participants were evaluated (127 men, 54 women; mean age ± standard deviation, 64.2 years ± 13.1; 75 striatum infarcts, 106 other locations). Visual inspection, SN-AI95, and average maps consistently showed higher SN R2* at 1 year if ipsilateral striatum was infarcted than if it was not (SN-AI95, 4.25 vs -0.88; P < .001), but this was not observed at baseline. The striatal location of the infarct was associated with higher SN-AI95 at 1 year independently from infarct volume, SN-AI95 at baseline, microbleeds, age, and sex (β = 4.99; P < .001). Voxel-based lesion-symptom mapping confirmed that striatum but also insula, internal capsule, and external capsule were associated with higher SN-AI95 at 1 year. SN-AI95 was an independent contributor of poor motor outcome (Box and Block Test, β = -.62 points; P = .01).

Conclusion

In patients with stroke, greater substantia nigra R2*, likely reflective of greater iron content, can be observed at 1 year ipsilateral from remote infarcts of specific location, which is associated with worse motor function.

© RSNA, 2019

Online supplemental material is available for this article.

See also the editorial by Vernooij in this issue.

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Article History

Received: Sept 13 2018
Revision requested: Oct 23 2018
Revision received: Dec 18 2018
Accepted: Jan 24 2019
Published online: Mar 12 2019
Published in print: May 2019