(A, B) Case 1, who presented with a brainstem syndrome. Axial T2 fluid-attenuated inversion recovery (FLAIR) images showing hyperintensity in the midbrain and mesial temporal lobe (arrows in A), which subsequently resolved on follow-up imaging performed at 2 months when the patient had relapsed with a polysymptomatic encephalopathy (B). (C, D) Case 2, who presented initially with a brainstem syndrome followed by periods of recurrent encephalopathy. Axial T2-weighted images 6 months after her initial brainstem syndrome revealed diffuse global cortical atrophy (C). Imaging during an encephalopathic episode 5 years later revealed new white matter changes (arrow in D) and further atrophy. This radiologic feature of leukoencephalopathy progressed on subsequent imaging (not shown). (E–H) Two patients with neurologic syndromes following herpes simplex virus encephalitis (HSVE). Serial axial T2 FLAIR images of case 4 (E–G) showing localized cortical changes in the left thalamus and occipital lobe (arrows in E) on initial imaging that progressed, demonstrating significant bilateral white matter signal changes in the parieto-occipital region 2 months later (arrows in F) when the patient presented with significant worsening of cognitive, behavioral, and motor regression. Following treatment and improvement of symptoms, follow-up neuroimaging 2 months later demonstrated a significant resolution of this white matter change (G). Axial T2-weighted image of case 5 at relapse 2 months after HSVE showing extensive bilateral but asymmetrical cystic encephalomalacia centered on the temporo-insular regions (only parietal changes shown) characteristic of HSVE, but in addition demonstrating the characteristic leukoencephalopathic changes seen globally (arrows in H). (I–L) Patients presenting with acquired demyelinating syndrome (ADS). At time of relapse with left optic neuritis, brain imaging in case 8 showed subtle periventricular white matter signal change on a T2-weighted image (arrow demonstrating one periventricular lesion in I). Imaging of case 9 showing midbrain (arrow in J), capsular (arrow in K), and thalamic changes (not shown) on axial T2 FLAIR. Axial T2 FLAIR image of case 10 demonstrating patchy subcortical white matter changes (L).