Low signal intensity and increased anisotropy on magnetic resonance imaging in the white matter lesion after head trauma: unrecognized findings of diffuse axonal injury.

We report on a four-year-old girl with head trauma caused by a motor vehicle accident. She presented with delirium, oculomotor palsy and ptosis in her left eye, left hemiparesis, and pyramidal signs in all extremities. Computed tomography on the day of admission showed diffuse cerebral edema with right-sided predominance. Magnetic resonance images on day 3 of admission showed lesions of diffuse axonal injury and contusion in the corpus callosum and right occipital and bilateral temporal lobes. There was a low-intensity lesion in the white matter of the right hemisphere on T2-weighted images, fluid-attenuated inversion recovery, T2()-weighted images, apparent diffusion coefficient maps and diffusion-weighted images. This low-intensity lesion disappeared by day 7, and a transient brain atrophy in the right hemisphere appeared on day 28. The low signal intensity in the cerebral white matter was apparently different from that associated with contusion and typical diffuse axonal injury, and might represent a late-onset accumulation of non-heme iron and free radicals in the white matter after head trauma.