Neurology Neurology · Emergency · High Yield

Raised ICP Signs

Raised intracranial pressure is a medical emergency. Its clinical features follow the Monro-Kellie doctrine and progress to herniation if untreated.

✦ The Mnemonic

"Cushing's Triad + Coning Signs — Brain Herniating"

Cushing's triad · Papilloedema · Headache · CN VI palsy · Herniation syndromes

C Cushing's triad Hypertension + bradycardia + irregular respirations — late, pre-terminal sign of severe raised ICP

H Headache Worse in the morning (recumbent position raises ICP overnight), on straining, coughing; positional

P Papilloedema Bilateral disc swelling — raised ICP transmitted down optic nerve sheaths; absent in acute ICP rise

VI CN VI palsy (false localising sign) Abducens stretched over petrous bone; lateral gaze palsy without pontine lesion

U Uncal herniation Ipsilateral CN III palsy (dilated pupil) → contralateral hemiplegia → coma → death

T Tonsillar herniation Cerebellar tonsils through foramen magnum → sudden respiratory arrest

📚 Clinical Breakdown

Monro-Kellie doctrine: the cranium is a rigid box containing brain (80%), blood (10%), and CSF (10%). An increase in any one component must be compensated by a decrease in another. Once compensation is exhausted, ICP rises sharply — the pressure-volume curve becomes exponential.

Management of raised ICP: 30° head elevation, head midline (avoid compressing jugular veins), correct hypovolaemia, target PaO2 >13 kPa and PaCO2 4.5–5 kPa (hyperventilation lowers ICP acutely), IV mannitol 0.25–1 g/kg, or hypertonic saline. Treat underlying cause (haematoma, hydrocephalus, tumour).

Idiopathic intracranial hypertension (IIH): raised ICP without structural cause. Young obese women. Headache, pulsatile tinnitus, papilloedema, visual field loss (arcuate scotoma progressing to blindness). Treat with weight loss, acetazolamide, and CSF diversion (LP shunt or optic nerve sheath fenestration if vision threatened).

Cushing's triad Hypertension + bradycardia + irregular breathing — pre-terminal

CN VI as false localising Stretched over petrous — not a pontine lesion

Uncal herniation sign Ipsilateral blown pupil (CN III compression)

IIH associations Young obese women; vitamin A excess; certain drugs

⭐ Clinical Pearl

LP contraindications in raised ICP: LP can cause fatal tonsillar herniation if performed in the presence of a posterior fossa mass or uncompensated raised ICP. Always perform CT head (and fundoscopy) before LP if: papilloedema, focal neurology, reduced GCS, immunocompromised, or age >60. Do NOT delay antibiotics for LP in suspected meningitis.

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