We report a case of a 42-year-old woman who developed fine motor dysfunction after decompressive craniectomy for traumatic brain injury (TBI), despite the absence of obvious lesions on conventional magnetic resonance imaging (MRI) to explain the motor deficits. Following cranioplasty, diffusion tensor imaging (DTI) revealed an increase in fractional anisotropy (FA) in the primary motor cortex, which correlated with significant improvement in motor function. These findings highlight DTI's potential as a valuable tool for capturing subtle brain changes not apparent on conventional imaging techniques.