7h • General discussion
🧠 Brain Herniation: The Silent Descent You Must Never Miss
Brain herniation is one of the most time-critical neurological emergencies we face.
It doesn’t shout at the beginning, it whispers.
But when it declares itself, deterioration can be rapid, dramatic, and irreversible.
Understanding the early signs, the mechanisms, and the clinical patterns is essential for anyone working in acute, critical, or emergency care.
🔍 What Is Brain Herniation?
Brain herniation occurs when rising intracranial pressure (ICP) forces brain tissue to shift from its normal position into adjacent compartments.
This displacement compresses vital structures, including the brainstem and threatens cerebral perfusion.
In simple terms:
👉 Too much pressure → not enough space → the brain is pushed somewhere it shouldn’t be.
This can be fatal within minutes if not recognised.
🧠 The Main Types of Brain Herniation
Here are the key herniation patterns you need to know:
1️⃣ Uncal (Transtentorial) Herniation
The medial temporal lobe is pushed under the tentorium.
Key features:
Unilateral fixed, dilated pupil (CN III compression)
Ptosis and “down and out” eye position
Reduced level of consciousness
Contralateral motor weakness → progressing to hemiplegia
Late: Cushing’s triad (hypertension, bradycardia, irregular respirations)
Think:
Pupil change = uncal herniation until proven otherwise
2️⃣ Central Herniation
Downward shift of the diencephalon and brainstem.
Early signs:
Subtle changes in consciousness
Small, reactive pupils
Respiratory pattern changes
Decorticate posturing
Late signs:
Fixed pupils
Flexor → extensor posturing changes
Cushing’s triad
Think:
A progressive decline with bilateral signs.
3️⃣ Subfalcine Herniation
Cingulate gyrus shifts beneath the falx cerebri.
Signs may be subtle:
Headache
Altered mentation
Weakness in one leg (compression of ACA territory)
Often an early warning before more dangerous herniation patterns occur.
4️⃣ Tonsillar Herniation
The cerebellar tonsils are forced down through the foramen magnum.
This is immediately life-threatening.
Key features:
Irregular or absent breathing
Neck stiffness
Altered consciousness → rapid decline
Cardiovascular instability
Pinpoint or non-reactive pupils
Think:
Tonsillar = respiratory arrest risk. Act now.
⚠️ Early Warning Signs You Must Not Ignore
Brain herniation rarely starts with dramatic deficits.
Look for these early red flags:
Sudden change in GCS
New or worsening headache
Vomiting (especially without nausea)
Behavioural change / agitation
Pupillary asymmetry
New focal deficit
New posturing
Cushing’s response:
↑ Blood pressure (widened pulse pressure)
↓ Heart rate
Irregular respirations
These signs indicate rising ICP and impending herniation.
🚨 Why It Happens
Common causes include:
Traumatic brain injury
Intracerebral haemorrhage
Subdural or epidural haematoma
Massive ischaemic stroke
Brain tumours
Hydrocephalus
Infections (meningitis, encephalitis)
Hypoxic injury with cerebral oedema
Any condition that increases intracranial pressure can trigger herniation.
🛠️ Emergency Priorities (General Principles)
While definitive treatment varies, the key goals remain consistent:
Protect airway and breathing
Maintain oxygenation and ventilation
Reduce ICP (e.g., head elevation, osmotherapy as appropriate)
Avoid hypotension — maintain cerebral perfusion
Urgent neuroimaging
Early neurosurgical involvement
Treat the underlying cause (bleed, tumour, infection, obstruction)
Time lost is brain lost.
📌 Why This Matters
Brain herniation is not just a diagnosis, it’s a neurological emergency with a narrow window for intervention.
Recognising:
the early clues
the evolving pattern
the characteristic signs
…may be the difference between recovery and irreversible damage.
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🧠 Brain Herniation: The Silent Descent You Must Never Miss
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