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Motor weakness is an important sequela after traumatic brain injury (TBI). Although the majority of cases of TBI are classified as mild TBI, little is known about motor weakness in mild TBI. In this study, we attempted to investigate injury of the corticospinal tract (CST), an important neural tract for motor function, in patients with mild TBI, using diffusion tensor tractography (DTT). There were 53 patients with mild TBI and 36 control subjects who were recruited. The patients were assigned to two groups according to the presence of abnormality of the right (dominant) hand function in terms of fine motor activity and grip strength: group A-abnormal hand function, group B-normal hand function. The left CST was reconstructed, and DTT parameters (fractional anisotropy [FA] and fiber number) and configuration were estimated. There were 35 (66%) patients who had an abnormal function of the right hand. The values of FA and fiber number of patient group A were significantly lower than those of patient group B and the control group ( p < 0.001). On configurational analysis of DTT for the left CST in patient group A, 80% showed partial tearing at the subcortical white matter and 20% showed narrowing. We found that in terms of DTT parameters and configuration, a significant portion of patients with mild TBI showed injury of the CST. These results suggest that DTT could provide useful information in detecting injury of the CST, and evaluation of the CST using DTT would be necessary for patients who complain of hand weakness after mild TBI. [ABSTRACT FROM AUTHOR]