Diffuse Axonal Injury (DAI)

Diagnosis Definition

• DAI (also referred to as traumatic axonal injury, or TAI) is a type of traumatic brain injury (TBI) resulting from accelerating and decelerating motion, with a rotational component, that leads to shearing of the white matter tracts of the brain
• Clinical presentation ranges from clinically insignificant findings to a comatose state
• The cause is usually high-speed motor vehicle accident but DAI can also result from child abuse (e.g., shaken baby syndrome)
• The outcome is frequently coma, with over 90% of patients with severe DAI never regaining consciousness; those who do wake up often remain significantly impaired

Imaging Findings

• DAI can be inferred when MRI, especially SWI or GRE sequences that are exquisitely sensitive to paramagnetic blood products, shows several small 1-15 mm ovoid or linear regions of susceptibility artifact (i.e., hemorrhage) at the grey-white matter junction (most commonly the frontal and temporal lobes), in the corpus callosum, and in more severe cases in the brainstem and pons, surrounded by FLAIR hyperintensity
• Surrounding edema increases in the first few days and usually resolves in 3 months on FLAIR images, whereas hemorrhagic changes on SWI may take 12 months to resolve; this is to be expected as edema is faster to resolve than hemorrhage

KEY IMAGES

Pearls

• There is no association between diffuse axonal injury and underlying skull fractures
• MRI is more sensitive than CT but MRI may also be normal in cases of DAI if edema isn’t present
• Diffusion tensor imaging can show findings of DAI even when MRI is negative

References

1. Davis PC. Head trauma. AJNR Am J Neuroradiol. 2007; 28(8):1619-21
2. Scheid R, Preul C, Gruber O, Wiggins C, von Cramon DY. Diffuse axonal injury associated with chronic traumatic brain injury; evidence from T2*-weighted gradient-echo imaging at 3T. AJNR Am J Neuroradiol. 2003; 24(6):1049-1056