Diffusion magnetic resonance imaging patterns in metabolic and toxic brain disorders.

PURPOSE: To evaluate metabolic and toxic brain disorders that manifest with restricted, elevated, or both restricted and elevated diffusion patterns on diffusion magnetic resonance imaging (MRI).
MATERIAL AND METHODS: Echo-planar diffusion MRI examinations were obtained in 34 pediatric patients with metabolic and toxic brain disorders proved by appropriate laboratory studies. The MRI unit operated at 1.5 T with a gradient strength of 30 mT/ meter, and a rise time of 600 micros. b=1000s/mm2 images and apparent diffusion coefficient (ADC) maps with ADC values were studied.
RESULTS: Three patterns were observed: 1. A restricted diffusion pattern (high signal on b = 1000 s/mm2 images and low ADC values); 2. an elevated diffusion pattern (normal signal on b = 1000s/mm2 images and high ADC values); and 3. a mixed pattern (coexistent restricted and increased diffusion patterns in the same patient). Disorders manifesting with a restricted diffusion pattern included metachromatic leukodystrophy (n = 2), phenylketonuria (n = 3), maple syrup urine disease (intermediate form) (n = 1), infantile neuroaxonal dystrophy (n = 1), Leigh (n = 2), Wilson (n = 3), and Canavan disease (n = 1). Disorders with an elevated diffusion pattern included phenylketonuria (n = 1), adrenoleukodystrophy (n = 1), merosin-deficient congenital muscular dystrophy (n = 2), mucopolysaccharidosis (n = 2), Lowe syndrome (n = 1), Leigh (n = 2), Alexander (n = 1), Pelizaeus-Merzbacher (n = 1), and Wilson (n = 3) disease. Disorders with a mixed pattern included L-2 hydroxyglutaric aciduria (n = 2), non-ketotic hyperglycinemia (n = 1), infantile neuroaxonal dystrophy (n =2), maple syrup urine disease (n = 1), and Leigh (n = 1) disease.
CONCLUSION: The findings suggested that the three different diffusion patterns reflect the histopathological changes associated with the disorders and different stages of a particular disorder. It is likely that the restricted diffusion pattern corresponds to abnormalities related to myelin, and the elevated diffusion pattern to disintegration of the tissue. The mixed pattern has contributions from both myelin abnormalities related to myelin disintegration of the tissue.