Unilateral deposition of paramagnetic substances in basal ganglia as early sign of neurodegeneration in magnetic resonance imaging

Purpose To describe a new radiological finding—an asymmetric deposition of paramagnetic substances in the ipsilateral basal ganglia to a mainly frontal supratentorial lesion—retrospectively observed via Magnetic Resonance (MR), using a Susceptibility Weighted Imaging sequence (SWI), and develop a reliable hypothesis of its possible origin in the context of a transsynaptic degeneration. Methods Following initial clinical observations of this specific MR sign, a systematic retrospective database review of the more recent reports of any case with a history of tumors or other frontal pathology was conducted, to evaluate using the SWI sequence if this asymmetric deposition of paramagnetic substances in the basal ganglia was consistently present. In addition, the identified cases (frontal pathology with asymmetric deposition of paramagnetic substances in the basal ganglia) showed signs of a pathology different from the one mentioned above, or in other areas of the brain, that could justify the presence of these deposits. Results Within the retrospectively evaluated cohort of 35 patients, the primary supratentorial etiologies were diverse, from tumors, ischemic pathology or previous surgery, and the predominant location was the frontal lobes. Different symptoms were present in 54.3% of the patients. According to the qualitative analysis carried out using the SWI sequences, this deposition tended to occur predominantly in the globus pallidus and substantia nigra ipsilateral to a supratentorial lesion. Furthermore, 11 out of the 35 cases (32%) had incipient anterograde degeneration of the ipsilateral corticospinal pathway. It should also be noted in post-surgical patients that this asymmetric deposition of paramagnetic substances did not exist in the studies prior to the intervention. Conclusion It is hypothesized that this structural asymmetry represents an early sign in MR in the context of transsynaptic degeneration with associated iron deposition in the basal ganglia. This hitherto undescribed finding could be important to further knowledge of the pathophysiology of basal ganglia, and could serve as a biomarker and prognostic factor in patients with frontal cortex pathology.