DWI 'starfield pattern' seen in this case refers to multiple bright foci of diffusion restriction on a dark background.
The timing of deterioration in this case is typical of fat embolism syndrome, with patients usually becoming symptomatic 24-72 hours after injury.
The main differential for cerebral fat embolism in a trauma patient will be diffuse axonal injury (DAI). In this case, the innumerable tiny foci of susceptibility artefact and diffusion restriction in a patient with four long bone fractures is highly likely to reflect fat embolism.