Diffuse Axonal Injury

KEY FACTS

Terminology

• Traumatic axonal stretch injury

Imaging

• General features

  • Can be hemorrhagic or nonhemorrhagic

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      Microbleeds important imaging marker for diffuse axonal injury (DAI)

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      Intraventricular hemorrhage correlates with DAI

  • Location

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      Subcortical/deep white matter (WM), corpus callosum

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      Deeper brain involvement = ↑ severity, poor prognosis

• NECT often normal (50-80%)

• MR

  • FLAIR: Hyperintense foci

  • T2* GRE: Hypointense “blooming” foci (hemorrhage)

  • SWI: Depicts significantly more DAI foci than GRE

  • DWI: May show restricted diffusion

Top Differential Diagnoses

• Multifocal nonhemorrhagic lesions

• Multifocal hemorrhagic lesions

Pathology

• Closed head injury (CHI)

  • Sudden deceleration, abrupt changes in angular momentum

• Cortex, WM have different densities, rotate at different speeds in CHI

  • Axons stretched (rarely disconnected or “sheared”)

  • Occurs at interfaces between tissues of differing density

• 80% of lesions are microscopic, nonhemorrhagic

Diagnostic Checklist

• Consider DAI if

  • Low GCS, minimal findings on NECT

• Remember

  • Deeper the abnormalities, more severe the brain injury

  • Remember: Visible lesions are “tip of iceberg”

TERMINOLOGY

IMAGING