Key Facts

Raised ICP is a life-threatening emergency requiring urgent identification and treatment. The cause must be identified and treated. Brainstem herniation (coning) is the final common pathway of death from raised ICP.

Epidemiology

Varies by cause. Common in neurosurgical and neurointensive care settings. TBI is the commonest cause of acute raised ICP. Space-occupying lesions are the commonest cause of subacute raised ICP.

Aetiology

• Increased CSF: hydrocephalus (obstructive or communicating), choroid plexus tumour
• Increased brain volume: cerebral oedema (cytotoxic — ischaemic stroke; vasogenic — tumour, abscess, infection; interstitial — hydrocephalus), mass lesion (tumour, haematoma, abscess)
• Increased blood volume: venous sinus thrombosis, arteriovenous malformation, hypertensive encephalopathy
• Other: idiopathic intracranial hypertension (pseudotumour cerebri), acute liver failure, hyponatraemia, high-altitude cerebral oedema

Pathophysiology

Monro-Kellie doctrine: the skull is a fixed-volume container. Compensatory mechanisms include displacement of CSF to spinal subarachnoid space and compression of venous sinuses. When compensation is exhausted, small increases in volume cause large rises in ICP (exponential pressure-volume curve). Raised ICP reduces cerebral perfusion pressure (CPP = MAP - ICP) → cerebral ischaemia. Brain herniation occurs when pressure gradients across dural folds cause brain displacement: transtentorial (uncal), subfalcine, cerebellar tonsillar (through foramen magnum → brainstem compression → death).

Symptoms

• Headache: worse on waking (recumbent position increases ICP), worse with coughing/straining/bending; progressive
• Nausea and vomiting: often projectile; especially early morning
• Visual disturbance: transient visual obscurations (brief bilateral visual loss on posture change), blurred vision, diplopia (CN VI palsy — false localising sign)
• Altered consciousness: drowsiness → stupor → coma

Signs

• Papilloedema: bilateral optic disc swelling on fundoscopy; may take hours-days to develop
• CN VI palsy: lateral rectus weakness → horizontal diplopia (false localising sign due to long intracranial course)
• Cushing response: systemic hypertension + reflex bradycardia + irregular (Cheyne-Stokes) respiration — LATE sign indicating brainstem compression
• Pupillary changes: ipsilateral fixed dilated pupil (CN III compression from uncal herniation)
• Decerebrate/decorticate posturing: brainstem dysfunction

Red Flags

• GCS deterioration → imminent herniation
• Fixed dilated pupil → uncal herniation (neurosurgical emergency)
• Cushing response → brainstem compression
• New onset seizures with mass lesion
• Papilloedema in any headache patient

Imaging (Urgent)

• CT head (non-contrast): first-line emergency investigation; identifies mass lesions, hydrocephalus, cerebral oedema, haemorrhage, midline shift
• CT with contrast: if abscess or tumour suspected
• MRI brain: superior for tumour characterisation, posterior fossa lesions, venous thrombosis
• CT/MR venogram: if cerebral venous thrombosis suspected

Bedside

• GCS: serial monitoring
• Fundoscopy: papilloedema
• Pupil size and reactivity: unilateral dilation → uncal herniation

Invasive Monitoring

• ICP monitoring (intraparenchymal bolt, external ventricular drain): gold standard in neurocritical care; target ICP <22 mmHg, CPP >60 mmHg

Lumbar Puncture

• CONTRAINDICATED if mass lesion or midline shift on CT (risk of coning)
• May be used therapeutically in IIH (after imaging excludes mass)
• Opening pressure: normal <25 cmH₂O; raised ICP >25 cmH₂O

Bloods

• FBC, coagulation, U&Es, LFTs: baseline
• Blood cultures: if infective cause suspected
• Osmolality: if mannitol being used

Emergency Measures (ABCs First)

• Airway protection: intubate if GCS ≤8
• Head elevation: 30° (improves venous drainage)
• Avoid hypotension: maintain MAP to preserve CPP (CPP = MAP - ICP; target CPP >60 mmHg)
• Avoid hypoxia: target PaO₂ >13 kPa
• Avoid hyperthermia and hyperglycaemia: active temperature and glucose management

Medical ICP Reduction

• IV mannitol 20%: 0.25-1 g/kg bolus over 15-20 minutes; osmotic diuretic; monitor serum osmolality (stop if >320 mOsm/kg)
• Hypertonic saline 3-5%: 2-5 mL/kg IV; alternative to mannitol; no osmolality ceiling; can be given via peripheral IV
• Hyperventilation: target PaCO₂ 4.0-4.5 kPa (temporising measure ONLY; excessive hyperventilation causes cerebral vasoconstriction → ischaemia)
• Dexamethasone 8-16 mg/day: for vasogenic oedema (tumours, abscess) — NOT for cytotoxic oedema (stroke, TBI)
• Sedation: propofol, midazolam — reduces cerebral metabolic demand

Surgical

• External ventricular drain (EVD): CSF drainage; diagnostic + therapeutic; first-line for hydrocephalus
• Decompressive craniectomy: large bone flap removal to allow brain swelling; reduces mortality in malignant MCA infarction and severe TBI (DECIMAL, DESTINY, RESCUEicp trials)
• Surgical excision: tumour resection, haematoma evacuation, abscess drainage
• VP shunt: for chronic hydrocephalus

Referral Criteria

• All acute raised ICP: neurosurgical emergency referral
• Neurocritical care for ICP monitoring
• Oncology: if underlying tumour

Depends on underlying cause and rapidity of treatment. Untreated raised ICP → brainstem herniation → death. Acute hydrocephalus: excellent prognosis if drained promptly. Malignant MCA infarction: decompressive craniectomy reduces mortality from ~70% to ~30% but significant disability in survivors. TBI: ICP >40 mmHg sustained → very poor prognosis. Brain tumour: depends on type, grade, and resectability.

Types of Brain Herniation

Cerebral Oedema Types