Paradoxical paramagnetic calcifications in the globus pallidus: An ex vivo MR investigation and histological validation study

Abstract

MR images based on phase contrast images have gained clinical interest as an in vivo tool for assessing anatomical and histological findings. The globus pallidus is an area of major iron metabolism and storage in the brain tissue. Calcium, another important metal in the body, is frequently deposited in the globus pallidus as well. Recently, we observed dense paramagnetic deposition with paradoxical calcifications in the globus pallidus and putamen. In this work, we explore detailed MR findings on these structures, and the histological source of the related findings using ex vivo CT and MR images. Ex vivo MR was obtained with a maximum 100 μm 3 isotropic resolution using a 15.2 T MR system. 3D gradient echo images and quantitative susceptibility mapping were used because of their good sensitivity to metallic deposition, high signal-to-noise ratio, and excellent contrast to iron and calcium. We found dense paramagnetic deposition along the perforating arteries in the globus pallidus. This paramagnetic deposition was hyperdense on ex vivo CT scans. Histological studies confirmed this finding, and simultaneous deposition of iron and calcium, although more iron dominant, was observed along the vessel walls of the globus pallidus. This was an exclusive finding for the penetrating arteries of the globus pallidus. Thus, our results suggest that several strong and paradoxical paramagnetic sources at the globus pallidus can be associated with vascular degeneration.

Clinical Implications of Focal Mineral Deposition in the Globus Pallidus on CT and Quantitative Susceptibility Mapping of MRI

“…The basal ganglia are an area of deposition of various kinds of minerals in the brain, including iron, calcium, copper, and magnesium [ 1 2 ]. In particular, the globus pallidus (GP) is a major area of metabolism and deposition of iron and calcium [ 2 3 4 ]. The deposition of these two abundant and important minerals is commonly encountered in the daily practice of neuroradiology [ 5 6 7 8 ].…”

“…The deposition of these two abundant and important minerals is commonly encountered in the daily practice of neuroradiology [ 5 6 7 8 ]. In addition to diffuse parenchymal deposition, there have been reports of focal deposition of iron and calcium at the medial aspect of the GP [ 3 5 9 ]. Of note, the preferential depositions of iron and calcium at the medial GP are similar but not identical [ 3 5 6 ].…”

“…In addition to diffuse parenchymal deposition, there have been reports of focal deposition of iron and calcium at the medial aspect of the GP [ 3 5 9 ]. Of note, the preferential depositions of iron and calcium at the medial GP are similar but not identical [ 3 5 6 ]. Previous histological studies reported focal depositions of iron and calcium at the medial aspect of the GP in and around the penetrating arterioles and perivascular spaces, as well as in the GP parenchyma [ 1 3 10 ].…”

“…Of note, the preferential depositions of iron and calcium at the medial GP are similar but not identical [ 3 5 6 ]. Previous histological studies reported focal depositions of iron and calcium at the medial aspect of the GP in and around the penetrating arterioles and perivascular spaces, as well as in the GP parenchyma [ 1 3 10 ]. Moreover, this mineralization of the GP increased with aging [ 9 11 ].…”

“…Considering the characteristic and opposing magnetic susceptibility of iron and calcium (paramagnetic iron and diamagnetic calcium), quantitative susceptibility mapping (QSM) could be an ideal approach for their assessment [ 4 12 13 ]. However, compared to the accuracy of QSM for the assessment of iron deposition, the value of QSM for calcium has been questioned, especially in the GP [ 3 5 ]. This may be associated with the dominance of iron deposition compared to calcium deposition, resulting in a negligible contribution of diamagnetic calcium to bulk susceptibility [ 3 5 ].…”