MRI Reveals Stroke Impact on Basal Brain

Measuring iron content in the brain using magnetic resonance imaging (MRI) could provide a clearer understanding of the consequences of a stroke, according to a new study.

Researchers at Centre Hospitalier Universitaire (CHU) de Bordeaux (France), Neurocentre Magendie (Bordeaux, France), and other institutions in France conducted a study to assess longitudinal changes in the substantia nigra (SN) in 181 patients who had suffered an ipsilesional supratentorial infarct, using an MRI technique called R2*. Study participants were evaluated once at 24–72 hours after the stroke (baseline visit), and again one year later.

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 side. The 95th percentile of R2* was then compared according to infarct location. The results revealed that one year after a baseline, some of the patients showed higher iron content in the SN. High iron content was found to be associated with worse long-term outcomes, particularly when it was found on the same side of the brain that the stroke occurred. The study was published on March 12, 2019, in Radiology.

“Overall, the SN is strongly involved in motor control, but also in regulation of emotions, cognition, and motivation. Usually, stroke doesn't directly affect the SN but, by interrupting circuits, stroke can induce secondary degeneration of that area,” said senior author Professor Thomas Tourdias, MD, PhD, of CHU Bordeaux. “We showed that imaging of iron can also be used to image degeneration remotely from stroke in disconnected areas. This finding could be clinically useful, because it shows that a simple magnetic resonance imaging method such as R2* can provide a more comprehensive picture of the consequences of an infarct.”

The SN is a basal ganglia structure located in the midbrain discovered in 1784 by Félix Vicq-d'Azyr. It is the largest nucleus in the midbrain. Humans have two SN, one on each side of the midline. It plays an important part in brain function, including eye movement, motor planning, reward-seeking, learning and addiction. Many of the SN’s effects are mediated through the striatum, and the SN also serves as a major source of GABAergic inhibition to various brain targets. The SN is critical in the development of many diseases and syndromes, including Parkinson's disease, which is characterized by the loss of dopaminergic neurons in the SN.

Related Links:
Centre Hospitalier Universitaire de Bordeaux
Neurocentre Magendie