What is the differential diagnosis?
1. Canavan disease: This usually affects the brainstem. The putamen and caudate nucleus are usually spared, as is the dentate nucleus. No antero-posterior gradient is seen. Markedly elevated NAA on MR spectroscopy. 2. Kearns-Sayre syndrome : The brainstem and thalamus are affected in most patients.
There is bilateral and symmetrical high signal of the white matter involving the subcortical U fibres. The deep white matter of the periventricular region and corpus callosum are preserved. The basal ganglia are of high signal, but the thalamus and brainstem are not affected. Marked signal change in the dentate nuclei is seen.
The areas of high T2/FLAIR intensity are of high signal on DWI (B=1000), but on subsequent ADC map this is shown to be due to T2 shine-through.
On ADC map, the regions of high T2/FLAIR intensity are shown to have increased diffusivity.