Diffusion MRI findings in phenylketonuria

Two patients with phenylketonuria were studied who were under dietary control since infancy, and who were mentally normal. Diffusion MRI was obtained using a spin-echo, echo-planar sequence with a gradient strength of 30 mT/m at 1.5 T. A trace sequence (TR=5700 ms, and TE=139 ms) was used, acquired in 22 s. Heavily diffusion-weighted (b=1000 mm²/s) images, and the apparent diffusion coefficient (ADC) values from automatically generated ADC maps were studied. There were two different patterns in these two patients, restricted and increased diffusion patterns. Restricted diffusion pattern consisted of high-signal on b=1000 s/mm² images with low ADC values ranging from 0.46 to 0.57×10⁻³ mm2/s. Increased diffusion pattern consisted of normal b=1000 s/mm² images with high ADC values ranging from 1.37 to 1.63×10⁻³ mm2/s. It is likely that these values reflected presence of two different histopathological changes in phenylketonuria or reflected different stages of the same disease.