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Raised intracranial pressure and herniation syndromes
The skull is a closed box: when one volume grows (tumour, blood, oedema, fluid), pressure rises, brain blood flow falls and finally brain tissue is pushed out (herniation) — so pressure is lowered in fast, ordered steps.
Why it matters in the exam
Questions present a patient with headache, vomiting, papilloedema and falling consciousness, or a patient who deteriorates with one dilated pupil, and ask what is happening and what to do. They test the cerebral perfusion pressure formula (mean arterial pressure minus intracranial pressure), Cushing's triad (hypertension, bradycardia and irregular breathing), herniation types by their signs, and the steps: head-of-bed elevation, osmotherapy (mannitol or hypertonic saline), brief hyperventilation as a bridge only, CSF drainage and decompressive craniectomy. Common distractors: lumbar puncture with mass effect, hypotonic fluids, prolonged hyperventilation, or steroids for head injury. A 6th nerve palsy is a "false localising sign" of raised pressure.
Key points
- Cerebral perfusion pressure is mean arterial pressure minus intracranial pressure.
- Cushing's triad: hypertension, bradycardia and irregular breathing.
- Uncal herniation: a dilated pupil on the same side and weakness on the opposite side.
- Treatment: head 30 degrees, mannitol or hypertonic saline, brief hyperventilation, drainage and sometimes surgery.
- No lumbar puncture with mass effect and no steroids for head injury.
Summary table
| Topic | Rule or finding | Note |
|---|---|---|
| Numbers | Cerebral perfusion pressure = mean arterial pressure minus intracranial pressure; treat when pressure is above 22 mmHg; perfusion target 60 to 70 mmHg | A fall in blood pressure is as harmful as a rise in intracranial pressure |
| Uncal herniation | A fixed dilated pupil on the same side (3rd nerve), weakness on the opposite side, falling consciousness | Sometimes weakness on the same side (false localising sign) |
| Central and subfalcine herniation | Central: falling consciousness, small pupils, decorticate and decerebrate posturing; subfalcine: anterior cerebral artery infarct — leg weakness | Central progresses from top to bottom |
| Tonsillar herniation | Neck stiffness, apnoea, sudden death | A lumbar puncture with mass effect may cause it |
| Stepwise treatment | Head of bed 30 degrees, neck straight, analgesia and treatment of fever and seizures; mannitol 0.25 to 1 g/kg or hypertonic saline; hyperventilation to PaCO2 30 to 35 as a short bridge | Ventricular drain, decompressive craniectomy; steroids only for oedema around a tumour |
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Sources
- Brain Trauma Foundation Guidelines for the Management of Severe Traumatic Brain Injury, 4th edition, 2016 — ICP and CPP thresholds
- Neurocritical Care Society Guideline for the Acute Treatment of Cerebral Edema, 2020 — Hyperosmolar therapy
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-06. The text may contain errors; when in doubt, check the source.