Iron distribution in the lentiform nucleus: A post-mortem MRI and histology study

Iron plays an important role in many neurobiological processes, especially in the basal ganglia, the brain structures with the highest concentration. Composed of the pallidum and putamen, the lentiform nucleus plays a key role in the basal ganglia circuitry. With MRI advances, iron-based sequences such as R2* and quantitative susceptibility mapping (QSM) are now available for detecting and quantifying iron in different brain structures. Since their validation using classic iron detection techniques (histology or physical techniques), these sequences have attracted growing clinical attention, especially in the field of extrapyramidal syndromes that particularly affect the basal nuclei. Accurate mapping of iron in these nuclei and their connections is needed to gain a better understanding of this specific anatomy, before considering its involvement in the physiopathological processes. We performed R2* and QSM along with Perls histology, to gain new insights into the distribution of iron in the lentiform nucleus and its surrounding structures, based on four specimens obtained from voluntary donors. We found that iron is preferentially distributed in the anterior part of the globus pallidus externus and the posterior part of the putamen. The lateral wall of the putamen is iron-poor, compared with the lateral medullary lamina and intraputaminal fibers. The relevance of perivascular iron concentration, along with pallido- and putaminofugal iron-rich fibers, is discussed.