Brain MRI Pattern Recognition in Neurodegeneration With Brain Iron Accumulation

Abstract

Most neurodegeneration with brain iron accumulation (NBIA) disorders can be distinguished by identifying characteristic changes on magnetic resonance imaging (MRI) in combination with clinical findings. However, a significant number of patients with an NBIA disorder confirmed by genetic testing have MRI features that are atypical for their specific disease. The appearance of specific MRI patterns depends on the stage of the disease and the patient's age at evaluation. MRI interpretation can be challenging because of heterogeneously acquired MRI datasets, individual interpreter bias, and lack of quantitative data. Therefore, optimal acquisition and interpretation of MRI data are needed to better define MRI phenotypes in NBIA disorders. The stepwise approach outlined here may help to identify NBIA disorders and delineate the natural course of MRI-identified changes.

Keywords: NBIA; iron; magnetic resonance imaging; neurodegeneration; pattern.

Figure 1

MRI hallmarks of PKAN (A–C), MPAN (D,E), and BPAN (F–H). In a PKAN patient with serial MRIs, the surrounding T2 hypointensity decreases in signal intensity with age (A,B, asterix). The PKAN-specific eye-of-the-tiger sign at the level of the anterior commissure (C-1) is better defined by the region-specific pattern of iron deposition on susceptibility-weighted image (C-2). In a younger patient with MPAN, T2- and T2*-weighted images shows preservation of isointense signal in the middle of inner and outer layers of iron accumulation (D-1, D-2, thin arrows). The typical streaking of the medial medullary lamina on T2-weighted image becomes more pronounced as signal intensity in the GP decreases, which is typically visible at the level of the anterior commissure (D-1, E-1). Brain MRI scans of three BPAN patients at different ages show age-related MRI changes. Brain MRI of a patient with BPAN at the age of 2 shows no abnormality on T2-weighted (F-1, F-2) and susceptibility-weighted (F-3, F-4) images. The substantia nigra is seen as hypointense on T2-weighted image (G-1, H-1) and hyperintense on T1-weighted image, whereas the central hypointense band is not demonstrated (G-2). T1-weighted image demonstrates hyperintensity of the substantia nigra and cerebral peduncle surrounding a central linear band of hypointensity, also known as the halo sign (H-2, thick arrow).