MRI of HEMS patients. Initial MRIs of patient 9 (A–D, age 3 years), and of an age-matched control (E–H, 2.5 years) and follow-up MRIs of patient 9 (I–L, age 12.4 years), and of an age-matched control (M–P, 12 years). All images are axial T2-weighted. MRIs of patient 9 show mild T2 hyperintensity of the medulla oblongata (A, arrow), the pons (B, white arrow) and the hilus of the dentate nucleus (B, black arrow). The thalamus is mildly T2 hyperintense, except for its ventrolateral part, which is dark (C, white arrow). The posterior limb of the internal capsule shows alternating hyperintense–hypointense–hyperintense stripes (C, black arrow). There is mild T2 hyperintensity of the optic radiation (C, white arrowhead) and the periventricular white matter that extends into the central subcortical white matter (D, black arrow). At later stages, the T2 signal in the medulla and pons improves (I and J), but the T2 hyperintensity of the optic radiation (K, white arrow), the corpus callosum (K, black arrow) and the periventricular white matter and subcortical white matter increases. Control images (E–H and M–P) show the normal myelination pattern with respect to age.