In a patient with high‑impact trauma (e.g., motor vehicle collision) who presents with loss of consciousness or coma but has a normal initial non‑contrast CT, how should diffuse axonal injury be diagnosed and managed?

Diffuse Axonal Injury: Diagnosis and Management

Immediate Diagnostic Approach

In a patient with high-impact trauma presenting with loss of consciousness or coma but a normal initial CT, you must proceed directly to MRI with specific sequences (T2-weighted gradient-echo, susceptibility-weighted imaging, and diffusion-weighted imaging) to diagnose diffuse axonal injury, as CT detects only 10% of DAI cases.* 1, 2

Initial Imaging Strategy

• Non-contrast CT remains mandatory as the first-line imaging in all patients with suspected moderate to severe traumatic brain injury, performed immediately upon presentation 3, 2, 4
• CT has severe limitations for DAI detection because microhemorrhages associated with axonal injury are frequently invisible on conventional CT, missing approximately 90% of cases 1, 2, 4
• When CT is normal but persistent unexplained neurologic findings exist (such as prolonged coma after high-impact trauma), MRI is indicated with a Class I recommendation 3, 1, 2, 4

Optimal MRI Protocol for DAI Detection

The American College of Radiology recommends the following specific sequences 1, 2, 4:

• T2-weighted gradient-echo (GRE) imaging*: Sensitive to microhemorrhages in acute, early subacute, and chronic stages of DAI 1
• Susceptibility-weighted imaging (SWI): 3-6 times more sensitive than T2* GRE for detecting hemorrhagic axonal injuries 1, 2
• Diffusion-weighted imaging (DWI): Visualizes non-hemorrhagic axonal injuries not appreciated on other sequences 1, 2

MRI can detect DAI lesions within the first 24 hours after injury, with approximately 27% of mild TBI patients with normal CT showing abnormalities on early MRI that improve prediction of 3-month outcomes 1, 2

Acute Physiological Management

Hemodynamic Targets

Maintain systolic blood pressure >110 mmHg to ensure adequate cerebral perfusion, as mortality increases markedly when systolic pressure drops below this threshold 3, 2, 4

• Avoid any episode of hypotension (SBP <90 mmHg), which compounds secondary brain injury 3, 2
• Use vasopressor drugs (phenylephrine, norepinephrine) for rapid correction rather than waiting for delayed effects from fluid resuscitation or sedative adjustment 3
• Avoid hypotensive agents for sedation induction 3

Ventilation Management

Control ventilation through tracheal intubation and mechanical ventilation with end-tidal CO2 monitoring (Grade 1+ recommendation), even during the pre-hospital period 3, 2, 4

• Prevent hypocapnia, which causes cerebral vasoconstriction and increases the risk of brain ischemia 3, 2, 4
• Target EtCO2 between 30-35 mmHg prior to obtaining arterial blood gas samples 3
• Pre-hospital tracheal intubation decreases mortality in trauma patients 3

Intracranial Pressure Management

• ICP monitoring is recommended for patients with severe TBI to detect intracranial hypertension, with intervention threshold typically at ICP >20 mmHg 2
• External ventricular drainage is suggested for treating persisting intracranial hypertension despite sedation and correction of secondary brain insults (Grade 2+ recommendation) 3, 2
• Decompressive craniectomy may be considered for refractory intracranial hypertension in multidisciplinary discussion 2

Prognostic Assessment

MRI-Based Prognostic Indicators

• The presence of both a contusion and >4 foci of hemorrhagic axonal injury on MRI is an independent prognostic predictor 1, 2, 4
• DAI grading correlates strongly with outcomes: Grade III DAI (dorsolateral brainstem lesions) is associated with poor outcomes and highest mortality 1, 2, 4
• The location and extent of DAI lesions correlate with clinical outcomes 1, 2

Important Caveat

• The number of microhemorrhages, while helpful for accurate diagnosis, is not currently thought to be associated with injury severity or outcomes 1

Management Strategies

Primary Treatment Principle

Management focuses on preventing secondary brain injury, as there is no specific treatment for the primary axonal damage itself 1, 2, 4

Rehabilitation Approach

• Early physical therapy and rehabilitation are essential to prevent joint contractures and muscle atrophy, including proper positioning, frequent repositioning, range of motion exercises, and splinting 2, 4
• Regular multidisciplinary case reviews are recommended for patients with severe DAI 1, 2, 4
• Early communication with regional neuroscience centers is essential for patients with perceived devastating brain injury 2, 4

Follow-up Imaging

• Follow-up imaging is indicated with neurological deterioration rather than on a routine basis 2
• Repeat CT is recommended for patients with epidural, subdural, and parenchymal hematomas, but may be less likely to alter clinical management in patients with subarachnoid hemorrhage 2

Common Pitfalls and Caveats

• Do not rely on CT alone: Only 10% of DAI is positive on CT because most lesions lack macroscopic hemorrhage 1, 2
• Do not use gadolinium-based contrast agents for conventional MRI in TBI (Class IIb recommendation) 1
• Diffusion Tensor Imaging (DTI) shows promise in research settings but has insufficient evidence to support routine clinical use at the individual patient level 1
• For elderly patients with severe injuries unlikely to be fully recoverable, early insertion of palliative medicine consultation improves outcomes, reduces in-hospital mortality and length of stay, and improves communication with family 2, 4