Diffusion Tensor Imaging Parameters in Children with Acute Hyperammonemic Encephalopathy due to Urea Cycle Enzyme Defects and Organic Acidemia

Background: Prolonged hyperammonemia, as a result of its toxic effect, may cause irreversible damage in the central nervous system. Objective: We aimed to determine whether there were DTI changes in brains of pediatric subjects with acute hyperammonemic encephalopathy due to Urea Cycle Defects (UCD) and Organic Acidemia (OA). Methods: Eleven children with acute hyperammonemic encephalopathy (UCD, n=5; OA, n=6) and 9 controls were included in study. Routine MRI and diffusion-weighted images at b= 0 s mm -2 and b= 1000 s mm -2 were applied. Then, DTI sequence was performed. ADC and FA comparisons of all subjects were performed by nonparametric tests (the Mann-Whitney test, Kruskal-Wallis test). Results: The mean ADCs of the perirolandic cortex (p=0.037), cerebellar white matter (p=0.006), cingulum (p=0.017), temporal and frontal periventricular white matter (p=0.030) (p=0.020), and parietal subcortical white matter (p=0.037) were statistically higher in all subjects than controls. FAs of nucleus caudatus (p=0.034), putamen (p=0.004), perirolandic cortex (p=0.026), corpus callosum genu (p=0.031), temporal periventricular white matter (p=0.003), and occipital periventricular and subcortical white matter (p=0.045, p=0.026) were lower in both subjects with UCD and OA than controls. FAs of splenium of the corpus callosum (p=0.012) in subjects with UCD were lower compared to subjects with OA and the control group. FAs of hippocampus and parietal subcortical white matter in subjects with OA were lower compared to subjects with UCD and the control group (p=0.031). Conclusion: On DTI, both UCDs and OAs demonstrated similar DTI changes in same regions compared to controls. These changes in ADC and FA values in both conditions may indicate microstructural damage. In this context, DTI findings may contribute to a better understanding of the underlying pathophysiology of disease.