## Investigation of Choice in Acute Head Injury with GCS ≤8 **Key Point:** Non-contrast CT head is the gold standard and most appropriate first imaging investigation in acute head injury with depressed GCS, regardless of focal neurological signs. **High-Yield:** In any patient with GCS ≤8 or signs of severe head injury (altered consciousness, focal deficits, skull fracture), immediate non-contrast CT head is mandatory before any other investigation or intervention. ### Rationale for CT Head **Clinical Pearl:** CT is superior to all other modalities in acute trauma because it: - Detects intracranial hemorrhage (epidural, subdural, subarachnoid, intracerebral) - Identifies cerebral contusion and diffuse axonal injury - Assesses midline shift and herniation risk - Is rapid (< 5 minutes) — critical in unstable patients - Guides urgent neurosurgical intervention **Tip:** GCS ≤8 is an absolute indication for intubation AND CT head. The patient's inability to protect airway is a separate ATLS priority (Airway management), but CT must be obtained urgently once airway is secured. ### Why CT, Not Other Modalities? | Investigation | Role in Acute Head Injury | Limitation | | --- | --- | --- | | **Non-contrast CT head** | Gold standard; detects acute bleeding, edema, shift | None in acute phase | | Skull X-ray | Outdated; poor sensitivity for intracranial injury | Misses 50% of significant injuries | | MRI brain | Excellent for diffuse axonal injury, posterior fossa lesions | Too slow (30–60 min); contraindicated if metallic foreign body; not for acute unstable patients | | Lumbar puncture | Contraindicated in acute head injury | Risk of herniation; CT must exclude mass effect first | **Warning:** Never perform LP before CT in head injury — risk of transtentorial herniation if mass effect is present. 
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