Diffuse axonal injury (DAI)

The patient was in a motor vehicle accident.


Findings

Non-contrast head CT demonstrates few punctuate hyper attenuating foci, including one near the gray-white junction in the right frontal lobe. MRI brain demonstrates multiple punctuate foci of T2/FLAIR prolongation, with corresponding restricted diffusion, within the subcortical frontal, temporal, and parietal lobes bilaterally. Most occur near the gray-white junction. The corpus callosum, deep gray matter structures, and brainstem are spared.

Differential diagnosis:
- Diffuse axonal injury.
- Multifocal nonhemorrhagic lesions:
Aging/microvascular ischemic disease
Demyelinating disease (MS, ADEM, etc.)
Marchiafava-Bignami syndrome
- Multifocal hemorrhagic lesions:
Cerebral amyloid angiopathy
Chronic hypertension
Cavernous malformation
Hemorrhagic tumors


Diagnosis: Diffuse axonal injury


Key points

Clinical Presentation
- Usually occurs in setting of high-speed MVC
- Transient loss of consciousness and retrograde amnesia common in minor traumatic brain injury
- LOC at moment of impact seen in moderate/severe TBI

Pathophysiology:
- Does not require direct impact to skull
- Occurs due to shear forces from differential acceleration/deceleration and rotational forces
- Cortex moves at different speed relative to underlying deep brain structures, creating axonal stretching.
- Non-traumatically disrupted axons are also damaged by traumatic depolarization, ion fluxes, and ultimately toxic edema.

50-80% of initial CT studies appear normal.
Hyper dense petechial hemorrhage, especially near gray-white junctions, seen in approximately20% of cases.
MRI is most-sensitive routine study for detection, especially when GRE sequences are utilized.

Typical MRI Findings:
- T1WI: Usually normal. May see hyper intense hemorrhage between 3-14 days.
- T2WI: Hyper intense foci seen at expected locations (gray-white junctions, corpus callosum, brainstem, uncommonly deep gray matter, internal/external capsules, corona radiata). Hemorrhagic lesions appear hypo intense on T2WI.
- FLAIR: Both hyper intense and hypo intense lesions at expected locations.
- DWI: Hyper intense foci of restricted diffusion.
- T2 GRE: Most sensitive sequence. Hypo intense foci due to susceptibility from blood products.

Increasing severity of traumatic force correlates with deeper brain involvement.

Staging based on Adams and Gennarelli system:
- Stage 1: Involves gray-white junctions of frontal and temporal lobes (mild)
- Stage 2: Involves corpus callosum and lobar white matter (moderate)
- Stage 3: Involves midbrain and pons (severe)