MR in phenylketonuria-related brain lesions

Purpose: Phenylketonuria (PKU) patients were examined by different MR techn iques to explain the pathological changes observed in periventricular white brain matter using conventional MR imaging. Material and Methods: Fifteen patients with treated classical PKU were exam ined by H-1 spectroscopy, relaxometry and diffusion imaging on a whole-body 1.5-T MR imager. Results: Known PKU lesions characterized by T2 enhancement in periventricul ar white matter were observed in all patients. The MR spectra from the lesi oned areas showed a significant decrease in choline concentration. The mean ADC of water decreased and tortuosity increased in PKU lesions compared to control data. Conclusion: The results support the following hypothesis: The T2 increase i n the PKU lesion reflects a raised concentration of free water molecules (a bout 15%) that have an increased trajectory between collisions compared to the same region in controls. The increase in water mobility might be explai ned by changes in extracellular space volume and myelin sheaths, which, pre sumably, have a different geometry with more hydrophobic sites in PKU patie nts. The changes result in increased tortuosity and may be confirmed by the loss of anisotropy in PKU lesions.