Raised Intracranial Pressure

Meet the patient

A 22-year-old man reaches resus after falling from his bike: he was talking at the scene, but his GCS has dropped from 14 to 11 in the last hour, his right pupil is bigger than his left, and his blood pressure is creeping up while his pulse slows. The CT scanner is warming up before anyone examines him further.[1]

Two questions decide the next thirty minutes — and they decide every raised-ICP case: is the brain herniating? (the pupil and the GCS trend answer that) and what is driving the pressure? (only the CT answers that, and only after it may you reach for a needle). Hold those two and the whole topic falls into place.[1]

The skull is a rigid box — Monro-Kellie governs everything

Raised ICP is a neurological emergency, and Monro-Kellie is the single idea that explains every sign, every threshold, and every treatment. The skull is a rigid, unyielding container holding three incompressible contents — so any rise in one must be bought by a fall in another, until the reserve runs out and pressure spikes.[1]

Normal intracranial pressure is 5 to 15 mmHg in a supine adult (about 7 to 20 cmH2O); in children about 1.5 to 10 mmHg, and in infants under 5 mmHg because the open fontanelles and unfused sutures lend extra compliance. Raised ICP is a sustained pressure over 20 mmHg in adults and over 15 mmHg in children; in traumatic brain injury the Brain Trauma Foundation 4th edition sets the treatment threshold at over 22 mmHg.[1]

As pressure climbs, cerebral perfusion pressure falls — CPP equals MAP minus ICP — the brain is starved of blood, and the brain substance is finally forced from one compartment to another: herniation. The most catastrophic form is tonsillar herniation (coning), where the cerebellar tonsils are driven through the foramen magnum, compressing the medulla into respiratory arrest and death.[1]

The discipline is simple and unforgiving: recognise the signs early, image urgently with non-contrast CT, lower the pressure, treat the cause — and never do an LP before the CT. One bedside error — a lumbar puncture in an unimaged mass, or steroids poured into a traumatic brain — and the patient dies of what was treatable.[1]

Classification — six mechanisms, four ways to herniate

Raised ICP sorts on two axes: the mechanism that adds intracranial volume, and the anatomical herniation syndrome the pressure finally produces. Monro-Kellie is the unifier — fixed total volume, so adding to one component costs another, until compensation is exhausted and the curve turns vertical.[1]

By mechanism the causes fall into clean groups: a space-occupying mass (tumour, haematoma, abscess) adds volume directly; hydrocephalus (obstructive or communicating) accumulates CSF; cerebral oedema (vasogenic, cytotoxic, osmotic, interstitial) swells the parenchyma; venous outflow obstruction (sinus thrombosis) blocks drainage; trauma adds blood and oedema; and idiopathic intracranial hypertension is the diagnostic leftover once every structural cause is excluded.[1]

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Cerebral oedema — four subtypes, only one likes steroids

Cerebral oedema is itself a major cause of raised ICP, and the examiner distinguishes four flavours deliberately. The discriminator that earns marks is steroid responsiveness.[1]

• Vasogenic — the blood-brain barrier leaks; fluid and protein escape into the extracellular space, classically around a tumour, abscess, or metastasis. Steroid-responsive — dexamethasone tightens the barrier.
• Cytotoxic (cellular) — intracellular swelling from sodium-potassium pump failure; the hallmark of ischaemic stroke, hypoxia, severe TBI. Not steroid-responsive.
• Osmotic — plasma osmolality drops rapidly (severe hyponatraemia, rapid correction, dialysis disequilibrium); water shifts into the brain.
• Interstitial — transependymal flow of CSF into the periventricular white matter in hydrocephalus.[1]

The classic trap lives here: steroids tighten the leaky barrier of vasogenic oedema — they do nothing for the dead cells of cytotoxic oedema, and CRASH proved they kill in trauma.[3]

Who gets it, and why

The epidemiology of raised ICP is the epidemiology of its causes — it is a syndrome, not a disease. In emergency practice traumatic brain injury is the commonest driver: severe TBI (GCS 3 to 8) raises ICP in over half of patients, and uncontrolled intracranial hypertension carries roughly 50 percent mortality.[1]

In neurosurgical series brain tumours (glioblastoma, metastases) and hydrocephalus lead; in paediatrics the headlines are congenital hydrocephalus (aqueduct stenosis, Dandy-Walker, Chiari II with myelomeningocele) and intraventricular haemorrhage of prematurity.[1]

Idiopathic intracranial hypertension has a demographic you can diagnose from the door: a young, obese woman of reproductive age. Incidence is about 1 per 100,000 in the general population but climbs to 19 per 100,000 in obese women of childbearing age, and rises further with body mass index. Obesity is the dominant modifiable risk factor, and weight loss of 5 to 10 percent is the single most effective treatment.[2]

Drug precipitants of IIH are worth a named list: tetracyclines (doxycycline, minocycline), vitamin A and retinoids (isotretinoin, hypervitaminosis A), combined oral contraceptive pill, lithium, growth hormone, anabolic steroids, and steroid withdrawal.[2]

Age reshapes the differential: infants — hydrocephalus and congenital malformations; children — posterior fossa tumours (medulloblastoma, ependymoma, pilocytic astrocytoma); young adults — IIH, venous sinus thrombosis, trauma; the elderly — subdural haematoma, metastases, and the swelling of a stroke.[1]

Monro-Kellie to herniation — the governing equation

Alexander Monro and George Kellie, in the 18th century, wrote the rule every intervention in this topic serves. The rigid skull holds a fixed volume of three incompressible components — brain about 80 percent, blood about 10 percent, CSF about 10 percent — so any addition to one must be offset by loss from another, or pressure rises.[1]

Early on, a growing mass is buffered by CSF displaced into the spinal subarachnoid space and venous blood squeezed into the extracranial veins. This is the flat, forgiving part of the volume-pressure curve — the patient looks well while the pressure quietly mounts.[1]

Once that compliance reserve is spent, the intracranial volume-pressure curve turns steep — a thimble of extra volume now produces an exponential pressure spike. This is decompensation, and it explains the tempo: the patient stable for weeks deteriorates over hours once the flat portion is used up.[1]

The same curve explains why coughing, straining, hypercapnia, seizures, and agitation can tip a compensated patient into crisis — each transiently raises intracranial blood volume. Every one of those converts straight into a treatment: normocapnia, normoxia, normothermia, analgesia, sedation, seizure prophylaxis.[1]

As ICP climbs, CPP falls — CPP = MAP minus ICP — and below about 60 mmHg the brain is ischaemic. Autoregulation, which normally holds cerebral blood flow constant across MAP 50 to 150 mmHg by adjusting arteriolar calibre, fails in the injured brain; perfusion then passively follows pressure, so a single hypotensive episode is directly injurious.[1]

This is why CPP 60 to 70 mmHg is the neurocritical-care target — too low starves the brain, too high worsens oedema and bleeds. A single systolic BP under 90 mmHg doubles mortality in severe TBI.[1][5]

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The four herniation syndromes — the UCTS-U face-off

Herniation is how raised ICP kills: brain is forced from one compartment to another through the rigid dural partitions (falx, tentorium) or the foramen magnum. Each syndrome leaves a recognisable pattern at the bedside.[1]

The four-syndrome face-off, each with a one-line discriminator:[1]

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Uncal is the commonest and most examinable. The medial temporal lobe is driven down through the tentorial hiatus, compressing in sequence the ipsilateral oculomotor nerve (a dilating, then fixed and dilated, pupil on the same side) and the ipsilateral cerebral peduncle (contralateral hemiparesis). Ipsilateral fixed dilated pupil with contralateral hemiparesis is the bedside signature.[1]

The classic false-localiser — Kernohan's notch. Occasionally the contralateral cerebral peduncle is crushed against the opposite tentorial edge, producing ipsilateral hemiparesis. The weak side then points away from the lesion, and the unwary operate on the wrong side.[1]

Central (transtentorial) is a symmetrical, axial downward shift of the diencephalon and brainstem — the result of diffuse bilateral pressure. It compresses in stages: diencephalon first (small reactive pupils, drowsiness), midbrain and pons next (midposition fixed pupils 3 to 5 mm, decorticate then decerebrate posturing), medulla last (irregular breathing, respiratory arrest). Diabetes insipidus may appear from hypothalamic-pituitary compression.[1]

Tonsillar (coning) is the feared one: the cerebellar tonsils are forced through the foramen magnum and compress the medulla, bringing respiratory arrest, loss of consciousness, and death within minutes. It is the reason a lumbar puncture performed in the face of raised ICP can kill — draining CSF from below builds a cranial-to-spinal gradient that sucks the tonsils down. This is the rationale for CT before LP.[1]

Subfalcine (cingulate) is the cingulate gyrus slipping under the falx cerebri, compressing the anterior cerebral artery against the rigid falx and producing contralateral leg weakness. It is often the earliest herniation with a frontal mass.[1]

Upward (cerebellar) herniation — the cerebellum driven up through the tentorial hiatus with a posterior fossa mass, compressing the midbrain and obstructing the aqueduct. It can be precipitated by a ventricular shunt that drains the supratentorial ventricles faster than it relieves a posterior fossa mass.[1]

The Cushing triad is pre-terminal — a medullary distress signal, not a screening sign. Sympathetic discharge drives the blood pressure up (the widened pulse pressure is the clue), the baroreceptor reflex answers with vagal bradycardia, and direct brainstem compression produces irregular (Cheyne-Stokes or ataxic) breathing.[1]

It is present in only about a third of fatal cases — so its absence never excludes raised ICP. When you do see it, act; do not wait to confirm.[1]

The cardinal quartet at the bedside

The cardinal quartet is headache, vomiting, papilloedema, and altered consciousness — but the tempo, pattern, and individual signs shift with the cause and the age, and the examiner probes the corners.[1]

Headache is the cardinal symptom and has a pattern you can recite in your sleep: worse on waking (a night lying flat raises cerebral venous pressure), worsened by coughing, sneezing, bending, or straining at stool (each briefly raises intrathoracic and hence intracranial venous pressure), and progressive over days to weeks rather than episodic. It is often relieved by vomiting and by standing, and is usually bifrontal or generalised.[1]

Contrast it at the bedside: tension (bilateral, pressing, end-of-day, no papilloedema); migraine (throbbing, photophobic, phonophobic, builds over hours with aura, relieved by sleep); cluster (unilateral periorbital, excruciating, lacrimation, in bouts).[1]

Vomiting in raised ICP is classically effortless and unexpected — not preceded by nausea — because it arises from direct compression of the medullary vomiting centre rather than the gut. Projectile vomiting is the classic paediatric sign.[1]

Papilloedema is the most specific sign but is often absent acutely — it takes hours to days to develop as axoplasmic flow is obstructed at the disc. The fundoscopy sequence: loss of spontaneous venous pulsations (earliest), then blurring of the disc margins (superior and inferior poles first), then disc elevation, and finally flame haemorrhages and cotton-wool spots in chronic disease.[1]

Everyone forgets: a normal fundus never excludes raised ICP. In the acute case the disc may look entirely normal — the falling GCS is the emergency, not the fundus.[1]

Altered consciousness runs from subtle cognitive slowing through drowsiness to deep coma. Document and trend the GCS — a fall of two or more points is an emergency demanding immediate imaging and escalation.[1]

At the bedside the herniation syndromes declare themselves: uncal — ipsilateral fixed dilated pupil with contralateral hemiparesis (beware Kernohan's notch flipping the side); subfalcine — contralateral leg weakness; central — bilateral pinpoint to midposition fixed pupils, posturing, coma; tonsillar — sudden respiratory arrest, sometimes in a patient who was talking moments before.[1]

Atypical presentations — the corners the examiner tests

The examiner tests atypical presentations on purpose. In the elderly, cerebral atrophy buys extra compliance, so a chronic subdural or a slow tumour reaches enormous size before it symptoms — presentation is later and subtler, often cognitive change, falls, anorexia, or a fluctuating conscious level rather than textbook headache.[1]

In children, especially pre-verbal, the signs are irritability, lethargy, head tilt (a posture to relieve pressure), vomiting, and in infants a bulging fontanelle and sunset sign (eyes driven downward, exposing sclera above the iris, from tectal plate compression).[1]

The IIH pattern is distinctive: a young obese woman with daily headache, transient visual obscurations (seconds, often on bending, from momentary optic nerve head ischaemia), pulsatile tinnitus (venous turbulence from raised venous pressure), diplopia from a sixth-nerve palsy (false-localising, from traction on the long vulnerable nerve as the brain shifts), and progressive visual field loss on perimetry. The risk that defines management is permanent blindness from chronic optic atrophy.[1]

The differential — and the LP-before-CT trap

The differential splits into other causes of headache, other causes of optic disc swelling, and other causes of acute coma — and the trap in each is reaching for the wrong pathway before the CT.[1]

The single distinction that protects the patient is IIH versus a posterior fossa tumour causing obstructive hydrocephalus — both give identical headache and papilloedema, which is why MRI/MRV is mandatory before the label "idiopathic" can be attached. Imaging reveals the tumour and the ventriculomegaly; without it, you are guessing.[2]

For acute coma with a normal CT, run through hepatic or metabolic encephalopathy, post-ictal state (especially non-convulsive status), intoxication (alcohol, opioids, benzodiazepines), sepsis, and hypertensive encephalopathy — each has its own urgent pathway, none of them is neurosurgery.[1]

The bedside round — find the sign that forces imaging

Examination in suspected raised ICP has one job: find the dangerous sign that demands immediate imaging and escalation.[1]

• GCS — document and trend hourly; a fall of two or more is an emergency. Reproduce the components: Eyes 1 to 4, Verbal 1 to 5, Motor 1 to 6; range 3 to 15. Intubate at GCS 8 or less.
• Fundoscopy — loss of spontaneous venous pulsations (earliest), blurred disc margins (poles first), disc elevation, then flame haemorrhages. A normal fundus never rules raised ICP out.
• Pupils — a unilateral fixed dilated pupil over 4 mm points to uncal herniation on that side until proven otherwise; bilateral midposition fixed (3 to 5 mm) suggest central; pinpoint suggests pons or opiates.
• Motor and focal exam — hemiparesis, Babinski, reflex asymmetry, any focal deficit pointing to a mass. Recall Kernohan's notch can flip the side.
• Vital signs — hunt the Cushing triad (rising BP with wide pulse pressure, falling pulse, irregular breathing); document temperature, since fever worsens ICP.
• Transorbital ultrasound — optic nerve sheath diameter over 5.0 to 5.8 mm measured 3 mm behind the globe is a rapid bedside surrogate, useful in ED or ICU while CT is arranged.
• False-localising sixth-nerve palsy — the long abducens nerve is tethered at the petroclinoid ligament; as the brain shifts it stretches, producing a lateral-rectus palsy with horizontal diplopia that does not localise the lesion — and is one of the modified Dandy criteria allowed in IIH.[1]

Investigations — CT first, always

Non-contrast CT — the FIRST test

The non-contrast CT brain is the first investigation in any suspected raised ICP, full stop. It is fast, ubiquitous, and answers the questions that decide the next move: is there a mass, a haematoma, hydrocephalus, midline shift, or effacement of the basal cisterns?[1]

The danger signs on CT: midline shift over 5 mm; effacement of the basal cisterns (ambient, quadrigeminal, suprasellar — a herald of impending herniation); loss of grey-white differentiation (cytotoxic oedema, ischaemia); compression or slit-like ventricles; and any obvious mass, haematoma, or infarct.[1]

MRI brain with MRV

MRI is second-line, for detail: posterior fossa lesions (no bone artefact), small tumours, and cerebral venous sinus thrombosis on MR venography. In the IIH workup MRI/MRV is mandatory — to exclude a venous sinus thrombosis or posterior fossa mass before "idiopathic" can be claimed. MRV shows absent or irregular venous flow in thrombosis.[1]

Lumbar puncture — contraindicated before imaging

Lumbar puncture before imaging is contraindicated in any suspected raised ICP, because of the risk of tonsillar herniation (coning) — draining CSF from below builds a cranial-to-spinal gradient that can force the cerebellar tonsils through the foramen magnum.[1]

The classic exceptions to "CT before LP": suspected meningococcal disease in a febrile patient with a non-blanching rash (give antibiotics immediately, do not delay for imaging), and the immunocompromised, in whom the threshold for imaging is even lower.[1]

In IIH, once CT/MRI is normal, the LP is both diagnostic and therapeutic. Measure the opening pressure in the lateral decubitus position with the legs relaxed (not flexed, which falsely elevates pressure). Opening pressure over 25 cmH2O in adults (over 28 cmH2O in children) confirms raised ICP; the CSF composition must be normal (cells, protein, glucose). Draining 20 to 30 mL can relieve the headache temporarily.[2]

The modified Dandy criteria — the four gates to "idiopathic"

The modified Dandy criteria exclude mimics and lock down the diagnosis:[2]

1. Signs and symptoms of raised ICP — headache, papilloedema, visual obscurations.
2. No localising neurological signs except a unilateral or bilateral sixth-nerve palsy (false-localising).
3. Raised CSF opening pressure over 25 cmH2O (adults) with normal CSF composition — no cells, normal protein and glucose.
4. Normal neuroimaging — no mass, no hydrocephalus, no venous sinus thrombosis on MRI/MRV.

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All four must hold; a posterior fossa tumour or a venous thrombosis is a secondary cause, not IIH. The label "idiopathic" is a diagnosis of exclusion earned only after the four gates pass.[2]

Invasive ICP monitoring — when, and with what

Place a monitor in severe TBI (GCS 3 to 8) with an abnormal CT, or a normal CT with two or more of: age over 40, motor posturing, systolic BP under 90 mmHg. The thresholds come straight from the Brain Trauma Foundation 4th edition.[5]

The intraventricular catheter (EVD) is the gold standard — it measures pressure directly and drains CSF therapeutically; its costs are invasiveness, ventriculitis risk, and difficulty placing it in a compressed ventricle. The intraparenchymal fibre-optic probe (Camino, Codman) is easier and cleaner but cannot drain and may drift.[1]

Modern multimodal monitoring layers on brain tissue oxygenation (PbtO2), microdialysis (lactate-pyruvate ratio for ischaemia), and continuous EEG — the injured brain is monitored, not just its pressure.[5]

Bloods

Routine bloods: glucose, urea and electrolytes, liver function, coagulation screen (before any neurosurgical procedure), full blood count and CRP for infection, and a drug or toxin screen if the coma is unexplained. In the anticoagulated patient, check the INR or anti-Xa urgently.[1]

The emergency bundle — head up, normocapnia, osmotherapy, treat the cause

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The emergency bundle treats secondary brain injury while the cause is found and fixed. The aim is constant — lower ICP, protect CPP — and every intervention either reduces intracranial volume or supports perfusion. The targets: avoid hypotension (keep systolic BP over 110, CPP 60 to 70), avoid hypoxia (SpO2 over 94 percent, PaO2 over 60), normocapnia, normoglycaemia, normothermia.[1]

• Airway and Breathing — intubate and ventilate if GCS is 8 or less. Give oxygen to keep SpO2 over 94 percent; hypoxia raises ICP by cerebral vasodilation and is directly injurious.
• Normocapnia — target PaCO2 4.0 to 5.0 kPa (35 to 40 mmHg). Brief mild hyperventilation to 4.0 to 4.5 kPa is reserved for the actively herniating patient as a temporising measure only. Prolonged hypocapnia below 4.0 kPa causes cerebral ischaemia and is harmful — hyperventilation is never a sustained strategy.
• Position — head of bed up 30 degrees, neck midline to drain the jugular veins. Avoid tight tube ties and any jugular compression; even turning the head impedes venous return.
• Perfusion — avoid hypotension (one systolic BP under 90 doubles mortality in severe TBI). Hold CPP 60 to 70 mmHg with isotonic fluids and noradrenaline as needed.
• Normoglycaemia and normothermia — treat fever (paracetamol, cooling) and seizures; both raise cerebral metabolic demand and ICP. Avoid tight glucose control — hypoglycaemia is injurious.
• Osmotherapy (first-line drugs) — mannitol 0.5 to 1 g/kg IV as a 20 percent solution over 10 to 15 minutes draws water out of the brain into the vascular space and is renally excreted; check serum osmolality and stop over 320 mOsm/L (acute kidney injury). Alternatively 3 percent hypertonic saline, about 250 mL bolus or 5 mL/kg, achieves the same gradient and suits the hypovolaemic or renally impaired. Both lower ICP within minutes.
• Clinical herniation — Cushing triad, a unilateral fixed dilated pupil, or a sudden GCS drop: emergency mannitol or hypertonic saline, hyperventilate briefly, urgent CT and neurosurgical referral. This is a load-and-go moment.[1]

The tiered ladder — escalate only when the lower tier fails

Neurocritical care escalates in tiers — each step adds power and risk, so escalation is deliberate and guided by ICP and CPP monitoring.[1][5]

Tier 0 — the basics

• Head up 30 degrees, neck midline to drain venous blood.
• Sedation and analgesia — propofol infusion or midazolam with fentanyl; lowers cerebral metabolic demand, agitation, and the sympathetic fight against the tube. Propofol can drop BP — watch CPP.
• The four normals — normoxia, normocapnia, normoglycaemia, normothermia.
• Seizure prophylaxis — phenytoin or levetiracetam for one week in severe TBI with an intracranial haematoma or depressed skull fracture (lowers early, not late, seizures).
• Treat fever — paracetamol and cooling; fever raises cerebral metabolic demand.[1]

Tier 1 — osmotic therapy

• Mannitol 0.25 to 1 g/kg IV bolus (20 percent solution), repeated guided by ICP and the osmolar gap (measured minus calculated over 20 mOsm/L signals a waning effect and renal risk). Check osmolality and renal function every 6 hours; stop over 320 mOsm/L.
• 3 percent hypertonic saline bolus (250 mL or 5 mL/kg) — useful in the hypovolaemic or renally impaired; monitor sodium, aim under 160 mmol/L.
• CSF drainage via an EVD — 5 to 10 mL aliquots can drop ICP immediately in a hydrocephalic patient.[1]

Tier 2 — metabolic suppression and surgery

• Barbiturate coma — thiopentone loading then infusion to suppress cerebral metabolic rate; titrate to burst suppression on continuous EEG. Risks: hypotension, immunosuppression, prolonged ICU stay.
• Decompressive craniectomy — a large frontotemporoparietal flap gives the swollen brain room to expand outward rather than downward. Reserved for refractory intracranial hypertension. RESCUEicp lowered mortality but at the cost of more vegetative and severely disabled survivors — a last-tier, shared-decision option, not a first-line treatment.[4]

Treat the cause — the only thing that actually cures raised ICP

• Evacuate an extradural, subdural, or intracerebral haematoma — an extradural drained before coning is one of neurosurgery's most rewarding operations.
• EVD or shunt for hydrocephalus.
• Resect or debulk a tumour; dexamethasone 4 to 8 mg QID (load 8 to 16 mg) for vasogenic oedema around a tumour or abscess.
• Antibiotics for a brain abscess or meningitis — empirical ceftriaxone plus metronidazole, guided by culture.[1]

The named trap that kills: corticosteroids are harmful in traumatic and ischaemic raised ICP. The CRASH trial (over 10,000 patients) showed intravenous corticosteroids increased mortality in TBI. Reserve dexamethasone for vasogenic oedema only — its mechanism is blood-brain barrier stabilisation, which does nothing for cytotoxic or traumatic oedema.[3]

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CSF shunts and diversion

For hydrocephalus, definitive treatment diverts CSF out of the cranium. The ventriculoperitoneal (VP) shunt is the workhorse — lateral ventricle to peritoneum, with a one-way valve (programmable or fixed-pressure) — and it serves both obstructive and communicating hydrocephalus.[1]

Endoscopic third ventriculostomy (ETV) is the alternative for obstructive hydrocephalus from aqueduct stenosis: a fenestration in the floor of the third ventricle lets CSF bypass the block to the basal cisterns, avoiding a shunt and its lifelong complications. The EVD is the temporary acute measure — monitoring plus therapeutic drainage in one line.[1]

Shunt complications are common and examinable: blockage (commonest — headache, vomiting, drowsiness); infection (Staph epidermidis or aureus — fever, meningism, track redness; remove and treat); overdrainage (ventricles collapse — slit-ventricle syndrome, orthostatic headache); underdrainage (persistent hydrocephalus).[1]

The syndrome of the trephined (sinking skin flap) is a delayed complication of decompressive craniectomy — the brain sinks under the absent bone flap as atmospheric pressure exceeds intracranial, and cranioplasty corrects it.[4]

IIH — the pseudotumour exception

Idiopathic intracranial hypertension — the pseudotumour exception

IIH is raised ICP with no structural cause — and it is the one raised-ICP syndrome that walks into outpatients rather than resus. The patient is a young, obese woman of reproductive age with daily progressive headache, transient visual obscurations, pulsatile tinnitus, papilloedema, and a false-localising sixth-nerve palsy.[2]

Diagnosis is the modified Dandy criteria (above): signs of raised ICP, no localising signs except a sixth palsy, opening pressure over 25 cmH2O with normal CSF, and normal MRI/MRV. The main risk is permanent blindness from chronic optic atrophy — visual loss is the indication for surgery.[2]

Treatment is staged: weight loss (5 to 10 percent, the single most effective move) plus acetazolamide — the IIH Treatment Trial proved it improves papilloedema and visual field function in mild-moderate disease. Surgery — optic nerve sheath fenestration or VP shunt — is reserved for vision-threatening disease.[2][6]

Severe traumatic brain injury — where the thresholds come from

In severe TBI (GCS 3 to 8) the secondary brain injury — hypoxia, hypotension, raised ICP — decides outcome far more than the primary impact. The Brain Trauma Foundation 4th edition sets the thresholds examiners quote: ICP monitoring in GCS 3 to 8 with abnormal CT (or normal CT with two of age over 40, motor posturing, systolic BP under 90); treat ICP over 22 mmHg; target CPP 60 to 70 mmHg; no prophylactic steroids (harmful — CRASH); multimodal monitoring in the most severe.[3][5]

Obstructive versus communicating hydrocephalus

Obstructive (non-communicating) — a block within the ventricular system: aqueduct stenosis, a posterior fossa tumour (medulloblastoma, ependymoma compressing the fourth ventricle), or fourth-ventricle outflow obstruction. Imaging shows ventriculomegaly proximal to the block (lateral and third dilated, fourth normal in aqueduct stenosis). Treat with EVD, VP shunt, or ETV (for aqueduct stenosis).[1]

Communicating — impaired CSF absorption at the arachnoid granulations: after subarachnoid haemorrhage (blood blocks the granulations), after meningitis (inflammatory debris), or with carcinomatous meningitis. All four ventricles dilate. Treat with a VP shunt — ETV does not help, because the block is at absorption, not within the ventricles.[1]

Cerebral venous sinus thrombosis

Cerebral venous sinus thrombosis presents with headache, papilloedema, and seizures, mimicking IIH in young prothrombotic women, but it can produce a venous infarct (often haemorrhagic) with focal deficits. Diagnose on MRV (absent or irregular venous flow).[2]

The key exam point: treat with anticoagulation (heparin then warfarin) even in the presence of haemorrhage. The bleed is venous, from back-pressure, and anticoagulation relieves the obstruction — a haemorrhagic venous infarct is treated with anticoagulation, not withheld from it.[2]

Herniation — the immediate bundle

Any herniation syndrome is an emergency: immediate osmotherapy (mannitol or hypertonic saline), hyperventilate briefly, urgent CT, and neurosurgery for decompression or evacuation. A unilateral fixed dilated pupil (uncal) with a temporal haematoma may reverse with emergency evacuation; tonsillar coning with respiratory arrest is often beyond salvage but deserves the full bundle.[1]

Complications and the preventable-harm list

The classic diagnostic pitfall is the LP before the CT in a patient with a mass — releasing the spinal gradient precipitates tonsillar herniation (coning). Always image first if there is any focal sign, reduced consciousness, papilloedema, immunocompromise, new-onset seizure, abnormal fundus, or a history suggesting a mass (progressive headache, vomiting).[1]

A second is corticosteroids in traumatic raised ICP — CRASH proved this raises mortality; dexamethasone is for vasogenic oedema (tumour, abscess) only.[3]

A third is prolonged hyperventilation — the early ICP fall from hypocapnia is bought with cerebral ischaemia, so hyperventilation is a bridge, not a strategy.[1]

The preventable-harm list — how raised-ICP patients die avoidably:[1]

• LP before CT — coning.
• Steroids in traumatic ICP — CRASH-proven mortality increase.
• Prolonged hyperventilation — cerebral ischaemia from sustained hypocapnia.
• Missing Cushing's triad as pre-terminal — waiting to confirm, instead of acting.
• A single hypotensive episode — doubles mortality in severe TBI.
• Bilaterally fixed dilated pupils left without the full bundle — they carry 70 to 90 percent mortality, but some reverse with emergency evacuation.[1]

Prognosis and disposition

Prognosis tracks the cause and the speed of treatment. In TBI-related raised ICP the prognostic factors are age, initial GCS, pupillary response (bilaterally fixed dilated pupils carry 70 to 90 percent mortality), the ICP control achieved, and the CPP maintained.[1]

Treatable causes can do beautifully — an extradural haematoma evacuated before coning is one of neurosurgery's great wins: the patient walks in with a headache and out neurologically intact. Severe TBI with uncontrolled ICP carries roughly 50 percent mortality; malignant tumours with mass effect do poorly on the tumour's own terms.[1]

In devastating brain injury with ICP uncontrollable through tier 0, tier 1, and decompressive craniectomy, the conversation moves to palliative care and withdrawal of life-sustaining treatment — a multidisciplinary decision with neurosurgery, intensive care, and the family, guided by prognostic signs (bilaterally absent pupillary and corneal reflexes, absent motor response, sustained ICP over 40 mmHg).[4]

Disposition: reduced consciousness, papilloedema, a monitored ICP, or an evolving deficit goes to ICU or neurocritical care; any surgical lesion (haematoma, hydrocephalus, tumour with mass effect) goes to theatre; stable IIH with intact vision can go to the ward with close perimetry and OCT follow-up.[1]

Special populations

• Infants — the open fontanelle and unfused sutures lend compliance, so the signs differ: bulging fontanelle (palpate calm and upright), splayed sutures, rapidly increasing head circumference (crossing centiles is a red flag), sunset sign, a high-pitched cry, irritability, vomiting. Causes: congenital hydrocephalus (aqueduct stenosis, Chiari II with myelomeningocele, Dandy-Walker), intraventricular haemorrhage of prematurity, congenital infections.
• Children — posterior fossa tumours (medulloblastoma, ependymoma, pilocytic astrocytoma) lead, often with ataxia, head tilt, vomiting, and obstructive hydrocephalus. Image any child with a progressive headache, one present on waking, or accompanied by vomiting or ataxia.
• Pregnancy — IIH is commoner (hormonal and weight changes). Distinguish from pre-eclampsia and eclampsia (hypertension, proteinuria, seizures, raised liver enzymes). Acetazolamide is generally avoided in the first trimester (theoretical teratogenicity) but considered safe in the second and third; weight management is key. Cerebral venous sinus thrombosis is also commoner in pregnancy and the puerperium.
• The elderly — cerebral atrophy lends compliance, so presentation is later and subtler (cognitive change, falls, fluctuating consciousness); a chronic subdural may reach enormous size before symptoms, especially when anticoagulated, presenting weeks after even minor trauma with a fluctuating conscious level.
• The anticoagulated patient — any new headache or reduced consciousness demands urgent CT and immediate reversal: warfarin with vitamin K plus prothrombin complex concentrate; dabigatran with idarucizumab; apixaban or rivaroxaban with andexanet alfa. Reverse empirically on suspicion — do not wait for the INR.
• The immunocompromised and HIV-positive — think toxoplasma abscess (ring-enhancing, sulphadiazine plus pyrimethamine), primary CNS lymphoma (periventricular, EBV-driven; steroids shrink it dramatically and confuse the biopsy — hold steroids until biopsy if lymphoma is suspected), and cryptococcal meningitis (raises ICP, may need repeat therapeutic LPs or a shunt).[1][2]

The trials, the guidelines, the regional deltas

Exam application bank (NEET-PG / INICET)

One-line answer

Raised intracranial pressure (ICP) occurs when the volume of brain, blood or CSF exceeds the rigid skull's capacity (Monro-Kellie doctrine). Normal ICP is 5 to 15 mmHg in a supine adult; in traumatic brain injury, ICP over 22 mmHg defines raised ICP and warrants treatment. Causes include space-occupying lesions (tumour, haematoma, abscess), hydrocephalus (obstructive and communicating), cerebral oedema (vasogenic, cytotoxic, osmotic), traumatic brain injury, cerebral venous sinus thrombosis and idiopathic intracranial hypertension (IIH). Presentation: headache (worse on waking, coughing, bending), nausea and vomiting, papilloedema, altered consciousness, and the Cushing triad (bradycardia, hypertension, irregular respiration — pre-terminal).[1]

Worked stems (answer without another resource)

Stem 1 — Classic presentation. Map symptoms to mechanism; name the first investigation and the first treatment step with dose and route if a drug is standard.[1]

Stem 2 — Unstable / complicated. List the red flags that force immediate resuscitation, theatre, ICU, antidote, or reperfusion — and what you do in the first 15 minutes.[1]

Stem 3 — Atypical group. Elderly, pregnancy, child, or immunocompromised: how presentation and thresholds change.[1]

Stem 4 — Differential trap. Name the three closest mimics and one discriminator for each.[1]

Stem 5 — Disposition. Who goes home with safety-netting, who is admitted, who needs HDU, ICU, or theatre, and what follow-up is mandatory.[1]

Rapid viva checklist

Run these ten in order — if you can speak to all ten unprompted, you have the topic.[1]

1. Definition plus classification
2. Pathophysiology chain
3. Bedside signs and criteria
4. Score with exact components (if any)
5. Emergency bundle
6. Definitive therapy with doses
7. Complications of disease and of treatment
8. Special populations
9. Guideline or trial name if classic
10. Three exam traps

[1]

Coverage self-check

If you cannot answer any stem above from this page alone, re-read the matching section — the page is meant to be self-sufficient for final-prof and NEET-PG/INICET questions on Raised Intracranial Pressure.[1]

Exam pearls

1. "Raised ICP: headache (worse on waking or coughing) plus vomiting plus papilloedema plus falling consciousness."[1]
2. "Cushing triad equals bradycardia plus hypertension with wide pulse pressure plus irregular respirations — pre-terminal brainstem herniation; its absence never excludes raised ICP."[1]
3. "CPP equals MAP minus ICP. Treat ICP over 22 mmHg (trauma); keep CPP 60 to 70 mmHg."[5]
4. "CT FIRST before LP — risk of coning. Never do LP first in a possible mass."[1]
5. "Acute: head up 30 degrees, neck midline, normocapnia (PaCO2 4.0 to 5.0 kPa), mannitol 0.5 to 1 g/kg or 3 percent hypertonic saline 250 mL, treat the cause."[1]
6. "IIH equals young obese women, papilloedema, normal MRI/MRV, LP pressure over 25 cmH2O, normal CSF. Treat: weight loss plus acetazolamide; surgery if vision threatened."[2]
7. "Herniation: uncal (ipsilateral fixed dilated pupil, contralateral hemiparesis) equals emergency. Tonsillar (coning) equals respiratory arrest and death. Central (pinpoint pupils, coma, DI). Subfalcine (ACA compression, contralateral leg weakness)."[1]
8. "Steroids for vasogenic oedema (tumour or abscess) ONLY — they are HARMFUL in traumatic raised ICP (CRASH trial)."[3]
9. "Monro-Kellie: rigid skull, fixed volume — brain about 80 percent, blood about 10 percent, CSF about 10 percent. Exhaust compensation and pressure spikes exponentially."[1]
10. "False-localising sixth-nerve palsy: long nerve stretched at the petroclinoid ligament as the brain shifts; does not localise the lesion."[1]

The mantra — the one line to carry

The mantra: the skull is a rigid box — when volume rises, perfusion falls and the brain herniates. Head up 30 degrees, normocapnia, osmotherapy, treat the cause — and CT before LP.[1]

Ward-round test — three stems, thirty seconds each

Stem 1 — the falling GCS after a fall (answer)

The 22-year-old from the top of the topic: GCS 14 to 11 in an hour, right pupil larger than left, BP rising and pulse slowing. Diagnosis set and first actions? Model: This is uncal herniation from an expanding intracranial mass (likely an extradural or subdural haematoma) — the asymmetric pupil is CN III compression, the rising BP with slowing pulse is the Cushing response (pre-terminal). Give emergency mannitol 0.5 to 1 g/kg IV (or 3 percent hypertonic saline), hyperventilate briefly to PaCO2 4.0 to 4.5 kPa, urgent non-contrast CT, and neurosurgical referral now for evacuation. Do not do an LP. Intubate if GCS is 8 or less.[1]

Stem 2 — the obese woman with daily headache (answer)

A 28-year-old woman, BMI 36, has daily headache for six weeks, seconds-long visual loss when she bends to pick up her child, pulsatile tinnitus, and bilateral disc swelling. CT is normal. What is the diagnosis, the next test, and the first treatment? Model: This is idiopathic intracranial hypertension until proven otherwise. Next test: MRI/MRV (exclude venous sinus thrombosis and a posterior fossa mass), then a lumbar puncture with opening pressure — over 25 cmH2O with normal CSF confirms it (modified Dandy criteria). First treatment: weight loss plus acetazolamide; serial perimetry and OCT to guard vision; surgery (ONSF or VP shunt) if vision is threatened.[2][6]

Stem 3 — the registrar who wants to give steroids (answer)

A severe TBI patient has rising ICP and cerebral oedema on CT. The registrar wants to add IV dexamethasone. What is the right call, and the trial that decides it? Model: No. Corticosteroids are harmful in traumatic and ischaemic raised ICP — the CRASH trial (over 10,000 patients) showed intravenous corticosteroids increased mortality in TBI. Reserve dexamethasone for vasogenic oedema only (tumour or abscess), where it stabilises the blood-brain barrier. For this patient: head up 30 degrees, normocapnia, mannitol or hypertonic saline, treat the cause — no steroids.[3]

References

1. [1]Kareemi H, Pratte M, English S, et al. Initial Diagnosis and Management of Acutely Elevated Intracranial Pressure J Intensive Care Med, 2023.PMID 36802976
2. [2]Wang MTM, Bhatti MT, Danesh-Meyer HV. Idiopathic intracranial hypertension: Pathophysiology, diagnosis and management J Clin Neurosci, 2022.PMID 34929642
3. [3]Edwards P, Arango M, Balica L, et al. Final results of MRC CRASH, a randomised placebo-controlled trial of intravenous corticosteroid in adults with head injury-outcomes at 6 months Lancet, 2005.PMID 15936423
4. [4]Hutchinson PJ, Kolias AG, Timofeev IS, et al. Trial of Decompressive Craniectomy for Traumatic Intracranial Hypertension N Engl J Med, 2016.PMID 27602507
5. [5]Hawryluk GWJ, Rubiano AM, Totten AM, et al. Guidelines for the Management of Severe Traumatic Brain Injury: 2020 Update of the Decompressive Craniectomy Recommendations Neurosurgery, 2020.PMID 32761068
6. [6]Wall M, McDermott MP, Kieburtz KD, et al. Effect of acetazolamide on visual function in patients with idiopathic intracranial hypertension and mild visual loss: the idiopathic intracranial hypertension treatment trial JAMA, 2014.PMID 24756514