Diffuse Axonal Injury
DAI

General Considerations

• Result of deceleration injuries, especially in high-speed motor vehicle collisions

• Also a major cause of morbidity in “Shaken Baby Syndrome”

• Most frequent cause of persistent vegetative state following trauma
• Result of rotational shear injuries that most often occur at the gray-white matter junction

• Extent of injury is usually worse than that depicted by imaging

• Shearing leads to edema, axoplasmic leakage, retraction ball formation and wallerian degeneration
• Brainstem function is typically unaffected

Clinical Findings

• Damage occurs at time of injury and then when secondary swelling occurs
• Immediate loss of consciousness

• Most, but not all, have no period of lucidity

• Brainstem functions remain intact so it is rarely a cause of death

Imaging Findings

• Diffuse
• Bilateral
• Majority of lesions (80%) are multiple
• Occur at the gray-white matter junction
• Lesions are most frequently ovoid, larger centrally than peripherally
• Frequently involved are the

• Frontal and temporal lobes
• Posterior body and splenium of the corpus callosum
• Caudate nuclei
• Thalamus
• Tegmentum
• Internal capsule
• More frequently associated with hemorrhage
• MRI is the preferred method of study but CT is usually more available

• On CT

• 50-89 of patients with DAI may have a normal CT scan on presentation
• Small petechial hemorrhages located at gray-white matter junction and  corpus callosum are characteristic but occur in only about 20%
• There may also be small. Focal areas of decreased attenuation secondary to edema

• On MRI

• Gradient-echo sequences are very useful in demonstrating paramagnetic effects of petechial hemorrhages
• Most common MRI finding
• Presence of multiple focal areas of abnormally bright signal on T2-weighted images in the white matter of the temporal or parietal corticomedullary junction or in splenium of corpus callosum.
• Hemorrhagic lesions appear hyperintense on T1-weighted images
• Non-hemorrhagic lesions appear hyperintense on T2-weighted sequences
• Gradient-echo sequences are very useful in demonstrating paramagnetic effects of petechial hemorrhages

Differential Diagnosis

• Multiple sclerosis
• Embolic or hemorrhagic stroke

Prognosis

• Over 90% remain in persistent vegetative state

• Chances of this occurring are greater with lesions that are supratentorial, involve the corpus callosum or corona radiata

• Prognosis worsens with multiplicity of lesions

Diffuse Axonal Injury. An axial, non-enhanced CT image of the brain demonstrates multiple small petechial hemorrhages at the gary-white matter junction, the caudate nucleus and the corpus callosum, characteristic of diffuse axonal injury in this male who was in a motor vehicle accident.
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Diffuse Axonal Injury  eMedicine  Wasserman, J; Koenigsberg, R