Diffuse Axonal Injury

Diffuse axonal injury results from rotational acceleration and deceleration producing widespread shear and stretch injury to axons.

The damage concentrates at junctions between tissues of different density.

Common sites include:

• Grey white matter junction
• Corpus callosum
• Dorsolateral upper brainstem
• Internal capsule
• Cerebellar peduncles

A patient can remain deeply unconscious despite a CT showing little haemorrhage because DAI is primarily microscopic.

Adams pathological grading

Grade I

Diffuse axonal injury in cerebral white matter, particularly at the grey white junction.

Grade II

Grade I injury plus corpus callosum involvement.

Grade III

Grade II injury plus brainstem involvement.

Grade III disease carries the greatest risk of prolonged coma and severe disability.

The classic presentation is immediate prolonged unconsciousness after high energy trauma.

Findings can include:

• Coma disproportionate to CT findings
• Abnormal posturing
• Autonomic instability
• Pupillary abnormalities with associated brainstem injury
• Prolonged impaired consciousness

A patient does not need to be permanently comatose to have DAI. Mild and moderate axonal injury can produce persistent cognitive and behavioural impairment.

CT can be normal or show only:

• Tiny haemorrhagic foci
• Mild cerebral swelling
• Small intraventricular haemorrhage

MRI: investigation of choice when DAI is suspected.

Useful sequences include:

• Diffusion weighted imaging
• Susceptibility weighted imaging
• T2 and FLAIR

MRI identifies small lesions within:

• Corpus callosum
• Brainstem
• White matter

MRI severity can inform prognosis but must not be used alone to declare neurological recovery impossible.

There is no operation that directly repairs diffuse axonal injury.

Management focuses on preventing secondary damage.

Use severe TBI principles:

• Avoid hypoxaemia
• Avoid hypotension
• Treat ICP above 22 mmHg when monitored
• Maintain CPP 60 to 70 mmHg
• Treat seizures
• Maintain normothermia
• Provide early nutrition
• Prevent VTE
• Begin rehabilitation when stable

Surgery is required only for associated treatable lesions such as:

• EDH
• SDH
• Large contusion
• Hydrocephalus
• Refractory intracranial hypertension requiring decompression

Prognosis

Recovery can continue for months.

Poor prognostic features include:

• Brainstem DAI
• Persistent fixed pupils
• Severe hypoxic or hypotensive secondary injury
• Prolonged unresponsive state

Do not use absence of early awakening after sedation withdrawal as a sole reason to assume futility.