Epidemiology & Risk Factors

Etiologies: MVCs (most common in young adults), falls (most common overall & in elderly/infants), assaults, sports-related trauma.
Risk Factors: Alcohol/substance use, advanced age, anticoagulant/antiplatelet therapy, lack of protective gear (helmets, seatbelts).
Classification by Glasgow Coma Scale (GCS):
- Mild: GCS 13–15 (includes concussion).
- Moderate: GCS 9–12.
- Severe: GCS ≤ 8 (defines coma; requires definitive airway).

Clinical Features

General Signs: Altered mental status (AMS), loss of consciousness (LOC), post-traumatic amnesia, headache, nausea/vomiting.
Signs of Increased ICP (Cushing Triad):
- Hypertension (widened pulse pressure).
- Bradycardia.
- Respiratory depression/irregular respirations.
Herniation Syndromes:
- Uncal (Transtentorial): Ipsilateral fixed & dilated pupil (blown pupil via CN III compression), contralateral hemiparesis.
- Subfalcine (Cingulate): Contralateral leg weakness (ACA compression).
- Tonsillar: Coma, flaccid paralysis, respiratory/cardiac arrest (cerebellar tonsils through foramen magnum).
Physical Exam Pearls:
- Basilar Skull Fracture: “Raccoon eyes” (periorbital ecchymosis), Battle sign (mastoid ecchymosis), hemotympanum, CSF rhinorrhea/otorrhea (clear discharge with “halo sign” / positive for $β$ -2 transferrin).

Diagnosis

Initial/Best Test: Non-contrast Head CT (NCCT).
- Indications for NCCT in mild TBI (Canadian CT Head Rule / New Orleans Criteria): GCS < 15 at 2 hrs post-injury, suspected open/depressed skull fracture, signs of basilar skull fracture, $\geq 2$ episodes of vomiting, age $\geq 65$ , retrograde amnesia $\geq 30$ mins, dangerous mechanism, coagulopathy/anticoagulant use.
Specific Imaging Findings:
- Epidural Hematoma (EDH): Biconvex (lenticular), hyperdense collection limited by cranial sutures (rupture of middle meningeal artery).
- Subdural Hematoma (SDH): Crescent-shaped, hyperdense (acute) or hypodense (chronic) collection crossing suture lines (rupture of bridging veins).
- Diffuse Axonal Injury (DAI): Multiple punctate hemorrhages at the grey-white matter junction; CT often normal or shows minimal changes disproportionate to severe clinical comatose state (MRI/DWI is most sensitive). c
- Subarachnoid Hemorrhage (SAH): Hyperattenuation in sulci, cisterns, and fissures.
Key Labs: Type & screen/crossmatch, CBC, BMP, PT/INR, PTT, toxicology screen, blood alcohol level, arterial blood gas (ABG).
Contraindication: Lumbar puncture is strictly contraindicated prior to neuroimaging due to risk of fatal brain herniation.

Differential Diagnostics

Epidural Hematoma (EDH):
- Diff: Classic lucid interval followed by rapid neurological decline; lens-shaped hyperdensity on NCCT.
Subdural Hematoma (SDH):
- Diff: Gradual insidious onset in elderly/alcoholics/infants; crescent-shaped hyperdensity crossing suture lines.
Diffuse Axonal Injury (DAI):
- Multifocal shearing tears and disruption of the axons of the brain due to rotational acceleration-deceleration trauma of the head; typically seen in high-impact road traffic accidents.
- Diff: Severe comatose presentation immediately post-high-speed acceleration-deceleration impact with near-normal initial NCCT; punctate lesions on MRI.
Concussion (Mild TBI):
- Diff: Functional rather than structural injury; transient cognitive deficit, normal NCCT, resolution typically within 1–3 weeks.
Ischemic / Hemorrhagic Stroke:
- Diff: Focal deficit matching vascular territory without preceding trauma; non-traumatic intraparenchymal bleed often deep (basal ganglia) secondary to chronic HTN.

Management

Initial Resuscitation (ABCs):
1. Airway: Intubate if GCS $\leq$ 8 or impending airway compromise (avoid nasotracheal intubation if basilar skull fracture suspected).
2. Breathing: Maintain normocapnia ( $P a C O_{2}$ 35–40 mmHg) and adequate oxygenation ( $P a O_{2} \geq 60$ mmHg, $S p O_{2} \geq 94%$ ).
3. Circulation: Maintain SBP $\geq 100$ mmHg (ages 50–69) or $\geq 110$ mmHg (ages 15–49, $\geq 70$ ) with isotonic crystalloids (NS/LR) to optimize Cerebral Perfusion Pressure ( $C P P = M A P - I C P$ ; Goal CPP 60–70 mmHg). Avoid hypotonic fluids (e.g., D5W, 0.45% NS $\to$ worsens cerebral edema).
Targeted Management of Elevated ICP ( $I C P > 22$ mmHg):
- Tier 1 (First-line):
  - Elevate Head of Bed (HOB) to 30° (promotes venous drainage).
  - Neck in midline position (avoid jugular compression).
  - Analgesia and sedation (reduces metabolic demand/ICP spikes).
- Tier 2 (Hyperosmolar Therapy):
  - Hypertonic saline (3%) (preferred in hypotension) OR Mannitol (osmotic diuretic; avoid if hypotensive/hypovolemic).
  - Temporary hyperventilation ( $P a C O_{2}$ 30–35 mmHg) reserved only as a brief rescue bridge for acute herniation (causes cerebral vasoconstriction $\to$ risk of ischemia if prolonged).
- Tier 3 (Refractory):
  - Neuromuscular blockade.
  - Moderate hypothermia.
  - High-dose barbiturates (e.g., Pentobarbital coma).
  - Decompressive craniectomy or surgical evacuation of space-occupying mass/lesion (indicated for midline shift $> 5$ mm or large hematoma volume).
Adjunctive Medical Therapy:
- Seizure Prophylaxis: Levetiracetam or Phenytoin for 7 days post-severe TBI (reduces early post-traumatic seizures; does not prevent long-term epilepsy).
- Reversal of Anticoagulation:
  - Warfarin: 4-Factor Prothrombin Complex Concentrate (4F-PCC) + IV Vitamin K.
  - Heparin: Protamine sulfate.
  - Direct Factor Xa inhibitors: Andexanet alfa or 4F-PCC.
  - Dabigatran: Idarucizumab.
- Contraindication: Glucocorticoids (e.g., Dexamethasone, Methylprednisolone) are contraindicated in moderate-to-severe TBI (proven to increase mortality).

Complications

Brain Herniation Syndromes (Uncal, central, subfalcine, tonsillar).
Post-Concussive Syndrome: Persistent headache, fatigue, dizziness, memory impairment, insomnia, and mood changes lasting weeks to months.
Post-Traumatic Epilepsy / Early Seizures.
Post-Traumatic Hypopituitarism: Anterior pituitary infarction from stalk shear injury.
Syndrome of Inappropriate ADH (SIADH) or Cerebral Salt Wasting (CSW) $\to$ Hyponatremia.
Diabetes Insipidus (Central DI) $\to$ Hypernatremia.
Chronic Traumatic Encephalopathy (CTE): Progressive neurodegeneration secondary to repetitive mild head impacts.

tags	—
aliases	Diffuse Axonal Injury

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Epidemiology & Risk Factors

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