Diffuse Axonal Injury

KEY FACTS

TERMINOLOGY

• Traumatic axonal stretch injury

IMAGING

• General features

○ Can be hemorrhagic or nonhemorrhagic

– Microbleeds important imaging marker for diffuse

axonal injury (DAI)

– Intraventricular hemorrhage correlates with DAI

○ Location

– Subcortical/deep white matter (WM), corpus callosum

– 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

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"

(Left) Most common sites of

axonal injury are shown in red;

frequent but less common

locations are in green. Injury

to the midbrain/upper pons

(purple) is uncommon but

often lethal; generally, the

deeper the abnormalities, the

more severe the injury. (Right)

Axial NECT scan in a 25-yearold man involved in a highimpact motor vehicle accident

(MVA) shows multiple

hemorrhagic foci in the

subcortical WM ſt, external

st and internal ﬇ capsules,

basal ganglia ﬈, and thalami

﬊. Blood is also present in 3rd

& lateral ventricles.

(Left) FLAIR MR in a 26-yearold man involved in a highspeed roll-over MVA shows

scattered hyperintense foci ﬈

in the subcortical and deep

WM consistent with diffuse

axonal injury. (Right) Axial SWI

in the same case shows

innumerable punctate and

linear hypointense foci ﬊ that

follow the course of the axons

within the corona radiata. T2*

scans (GRE, SWI) are very

sensitive to susceptibility

artifact from hemorrhage.

Brain: Pathology-Based Diagnoses: Malformations,

Trauma, and Stroke

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