A 32-year-old man is brought to the emergency department following a road traffic accident with severe head injury. On examination, he has a GCS of 7/15 with bilateral pupillary dilation and decorticate posturing. Which is the most common cause of death in the first 48 hours following severe head injury in trauma patients?

## Most Common Cause of Death in Severe Head Injury **Key Point:** Acute subdural hematoma and diffuse axonal injury are the most common *pathological findings* in fatal head injuries, but **transtentorial herniation secondary to raised intracranial pressure** is the most common *mechanism of death* in the first 48 hours. ### Pathophysiology of Death in Severe Head Injury In the hyperacute phase (0–48 hours), death results from: 1. Massive elevation of intracranial pressure (ICP) 2. Compression and displacement of brainstem structures 3. Herniation (transtentorial, uncal, or central) 4. Loss of vital brainstem reflexes (respiration, cardiovascular control) **Clinical Pearl:** The classic triad of Cushing's response (hypertension, bradycardia, irregular respiration) signals impending brainstem herniation and is a pre-terminal event. ### Why Other Lesions Are Not the Primary Cause of Death | Lesion | Why Not Primary Cause of Death | Timing | |--------|--------------------------------|--------| | **Diffuse Axonal Injury (DAI)** | Present in ~45% of fatal head injuries but causes death via secondary effects (seizures, metabolic derangement) over hours–days, not immediate herniation | Delayed | | **Acute Epidural Hematoma** | Accounts for only 5–10% of fatal head injuries; most are treatable with urgent evacuation if diagnosed early | Varies; often later | | **Acute Subdural Hematoma** | Most common *pathological finding* (40–45% of fatal cases) but death occurs via mass effect → raised ICP → herniation, not the hematoma itself | Hours–days | **High-Yield:** The mechanism of death is **raised ICP → brain herniation → brainstem compression → loss of vital functions**. The underlying lesion (SDH, DAI, etc.) is the *cause* of raised ICP, but herniation is the *cause of death*. ### GCS and Prognosis A GCS of 7/15 with bilateral pupillary dilation and decorticate posturing indicates: - Severe diffuse brain injury - Likely uncal herniation (dilated pupil = CN III compression) - Imminent brainstem failure **Mnemonic: SLUDGE** — Signs of brainstem herniation: **S**alivation, **L**acrimation, **U**rination, **D**efecation, **G**astrointestinal upset, **E**mesis (actually parasympathetic — but in herniation, you see the *opposite*: dry mouth, fixed pupils, apnea). [cite:Harrison 21e Ch 423]