Quantitative Differentiation Between Healthy and Disordered Brain Matter in Patients with Neurofibromatosis Type I Using Diffusion Tensor Imaging

Abstract

BACKGROUND AND PURPOSE: Hyperintensities on T2-weighted images are seen in the brains of most patients with neurofibromatosis type I (NF-1), but the origin of these unidentified bright objects (UBOs) remains obscure. In the current study, we examined the diffusion characteristics of brain tissue in children with NF-1 to test the hypothesis that a microstructural abnormality is present in NF-1.

MATERIALS AND METHODS: Diffusion tensor imaging (DTI) was performed in 50 children with NF-1 and 8 controls. Circular regions of interest were manually placed in 7 standardized locations in both hemispheres, including UBO sites. Apparent diffusion coefficients (ADC), fractional anisotropy (FA), and axial anisotropy (A_m) were used to differentiate quantitatively between healthy and disordered brain matter. Differences in eigenvalues (λ₁, λ₂, λ₃) were determined to examine parenchymal integrity.

RESULTS: We found higher ADC values for UBOs than for normal-appearing sites (P < .01) and higher ADC values for normal-appearing sites than for controls (P < .04 in 5 of 7 regions). In most regions, we found no differences in FA or A_m. Eigenvalues λ₂ and λ₃ were higher at UBO sites than in normal-appearing sites (P < .04).

CONCLUSION: With ADC, it was possible to differentiate quantitatively between normal- and abnormal-appearing brain matter in NF-1 and also between normal-appearing brain matter in NF-1 and healthy brain matter in controls, indicating subtle pathologic damage disrupting the tissue microstructure in the NF-1 brain. Higher diffusivity for λ₁, λ₂, and λ₃ indicates that this disturbance of microstructure is caused by accumulation of fluid or vacuolation.