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).