Diffusion tensor MR imaging tractography of the pyramidal tracts correlates with clinical motor function in children with congenital hemiparesis

Abstract

Background and purpose: Children with congenital hemiparesis have greater asymmetry in diffusion parameters of the pyramidal tracts compared with control subjects. We hypothesized that the asymmetry correlates with the severity of hemiparesis and that diffusion metrics would be abnormal in the affected tracts and normal in the unaffected tracts.

Materials and methods: Fifteen patients with congenital hemiparesis and 17 age-matched control subjects were studied with diffusion tensor MR imaging tractography. Hemipareses were scored as mild, moderate, or severe. We measured tract-specific diffusion parameters (fractional anisotropy, mean, and directional diffusion coefficients) of the pyramidal tracts. We compared tract-specific parameters and asymmetry between the right and left tracts of the differing severity groups and control subjects.

Results: We observed many different causes of congenital hemiparesis including venous infarction, arterial infarction, and polymicrogyria. Clinical severity of hemiparesis correlated with asymmetry in fractional anisotropy (P < .0001), transverse diffusivity (P < .0001), and mean diffusivity (P < .03). With increasing severity of hemiparesis, fractional anisotropy decreased (P < .0001) and transverse diffusivity (P < .0001) and mean diffusivity (P < .02) increased in the affected pyramidal tract compared with controls. Diffusion metrics in the unaffected tract were similar to those in the control subjects.

Conclusion: Asymmetry in fractional anisotropy, transverse diffusivity, and mean diffusivity, as well as the degree of abnormality in the actual values of the affected pyramidal tracts themselves, correlates with the severity of motor dysfunction in infants and children with congenital hemiparesis from different causes. This suggests that abnormalities detected by diffusion tensor MR imaging tractography in the affected pyramidal tract are related to the functional ability of the affected pyramidal tract, regardless of the etiology of motor dysfunction.

Fig 1.

Color-coded representation of fractional anisotropy in the pyramidal tracts of a control subject (A), a patient with mild left hemiparesis (B), a patient with moderate left hemiparesis (C), and a patient with severe left hemiparesis (D). Lower fractional anisotropy values are seen in the affected pyramidal tract compared with the unaffected tract of the patients with moderate and severe hemiparesis. The patient with mild hemiparesis and the control subject show no appreciable asymmetry. Although the entire tract is shown from the level of the cerebral peduncle to the centrum semiovale, the analysis was limited to that portion of the pyramidal tract between the posterior limb of the internal capsule (outlined in green) and the cerebral peduncle (see Methods).

Fig 2.

Comparison of diffusion parameters in affected and unaffected tracts of the patients with normative curves. Fractional anisotropy (A), transverse diffusivity (B), D_av (C), and parallel diffusivity (D) are plotted against age for the patients with mild hemiparesis (circles), those with moderate hemiparesis (squares), and those with severe hemiparesis (triangles). Both affected (solid symbol) and unaffected (open symbol) pyramidal tract diffusion values are plotted for each patient. Values are compared with the normative curves (dashed curve) of the natural logarithm of the diffusion metric versus age (see Methods).