Increased ICP
Increased intracranial pressure is an elevation of pressure within the cranial vault above 20 mmHg, caused by expanding mass lesions, cerebral edema, or impaired cerebrospinal fluid circulation, potentially leading to brain herniation and death.
Increased intracranial pressure (ICP) — also termed raised ICP or intracranial hypertension — refers to a sustained elevation of the pressure within the rigid cranial vault above the normal physiological range.
- Adult normal ICP = 10–15 mmHg [1]
- Infant normal ICP = 1–6 mmHg [1] (lower because of open fontanelles and unfused sutures that provide compliance)
- Young children: 3–7 mmHg [2]
- Definitely abnormal > 20 cmH₂O (≈ 15 mmHg); sustained ICP > 20–22 mmHg warrants treatment in most neurosurgical guidelines (Brain Trauma Foundation, 4th edition, 2016/2020 update) [1]
Break down the term: "Intra" = within, "cranial" = skull, "pressure" = force per unit area. So we are literally talking about the force exerted by the skull's contents against the inner table of the skull.
Why does raised ICP matter?
It matters for two reasons [2]:
- Global effect — ↓ cerebral blood flow → cerebral ischaemia
- Focal effect — pressure gradients across dural compartments → brain herniation → brainstem compression → death
Raised ICP is not a disease in itself — it is a pathophysiological state complicating many conditions. Its epidemiology therefore mirrors its causes:
| Risk factor / context | Why it matters |
|---|---|
| Traumatic brain injury (TBI) | Most common acute cause worldwide. In Hong Kong, RTA and falls (especially in elderly) predominate. Up to 50–75% of patients with severe TBI (GCS ≤ 8) develop raised ICP |
| Intracranial tumours | Second most common cause overall. Adults: 70% supratentorial (metastases, meningioma, GBM). Children 2–12 y: 70% infratentorial (medulloblastoma, pilocytic astrocytoma, ependymoma) [3] |
| Stroke (large territory infarct, ICH, SAH) | Malignant MCA syndrome, large cerebellar infarct, and hypertensive ICH are common in HK's ageing population |
| CNS infections | TB meningitis remains a significant cause in Hong Kong; bacterial meningitis, brain abscess, cryptococcal meningitis (especially HIV) |
| Hydrocephalus (congenital or acquired) | Congenital: aqueductal stenosis, Chiari malformations, Dandy-Walker. Acquired: post-SAH, post-meningitis, tumours |
| Idiopathic intracranial hypertension (IIH) | Incidence ~1–2/100,000/y; overwhelmingly in obese women of child-bearing age [2] |
| Age extremes | Infants: unfused sutures → can compensate longer, but when overwhelmed, present with bulging fontanelle. Elderly: brain atrophy provides initial compliance, but once exhausted, ICP rises steeply |
| Anticoagulant / antiplatelet use | ↑ risk of intracranial haemorrhage in the elderly HK population (high use of warfarin, DOACs for AF) |
| Chronic hypertension | Major RF for hypertensive ICH (commonest sites: pons, cerebellum, putamen, thalamus) [4] |
Relevant Anatomy & Physiology
The adult skull is a closed, rigid box (unlike the infant skull, which has open fontanelles and unfused sutures). This is the foundation of everything that follows.
"The skull is a rigid structure with constant volume. The content of skull = brain (80%) + blood (10%) + CSF (10%). Therefore, ↑ in any constituent must be compensated by ↓ in others." [1][2]
Compensatory mechanisms (in order of recruitment):
- CSF displacement — CSF flows out of the cranium into the spinal subarachnoid space (slow mechanism)
- Venous blood displacement — venous blood is squeezed out via the jugular veins (fast mechanism)
- Brain compliance — very limited; brain tissue is essentially incompressible
Once these buffers are exhausted, even a tiny additional volume causes a dramatic rise in ICP. This is shown in the classic ICP-volume curve (exponential):
Exception: in infants, ↑ ICP causes suture diastasis [2] — the sutures can splay apart, providing extra compliance, which is why infants can tolerate slowly expanding lesions longer but present with an enlarging head.
- Production: Choroid plexus in ventricles, ~450 mL/day in adults [1]
- Absorption: Arachnoid granulations (villi) at venous sinuses [1]
- CSF volume at any time ≈ 150 mL (half intracranial, half spinal)
- CSF flows: lateral ventricles → interventricular foramen (of Monro) → 3rd ventricle → cerebral aqueduct (of Sylvius) → 4th ventricle → foramina of Luschka (lateral) and Magendie (median) → subarachnoid space → arachnoid granulations → superior sagittal sinus → venous system
Hydrocephalus occurs if: ↑ Production, Flow obstruction, or ↓ Absorption [1]
These are the clinical surrogates for adequate brain perfusion [5]:
(If ICP > JVP; otherwise CPP = MAP − JVP)
Where:
- CPP = Cerebral Perfusion Pressure
- MAP = Mean Arterial Pressure
- ICP = Intracranial Pressure
- CVR = Cerebrovascular Resistance
- CBF = Cerebral Blood Flow
Why is this important? If ICP rises without a matching rise in MAP, CPP falls → CBF falls → the brain becomes ischaemic. In severe cases, when ICP approaches MAP, CPP → 0 → brain death.
- Normal: For MAP ~50–150 mmHg, the cerebral vasculature adjusts its resistance (CVR) to keep CBF constant (~50 mL/100 g/min). This is called pressure-active autoregulation.
- In chronic hypertension: the autoregulation curve shifts rightward [5] — meaning the brain now requires a higher MAP to maintain the same CBF. This is why aggressive BP lowering in a chronically hypertensive patient can cause cerebral ischaemia.
- In TBI: autoregulation is impaired (the system becomes pressure-passive) [6] — any drop in MAP directly translates to a drop in CBF → ischaemia. This is why maintaining adequate MAP is critical in head-injured patients.
Clinical Pearl: Autoregulation in TBI
A common mistake is to aggressively lower blood pressure in a head-injured patient with concurrent raised ICP. Because autoregulation is impaired, the brain is dependent on systemic BP for perfusion. Dropping MAP will drop CPP and worsen secondary brain injury. The target is to keep CPP ≥ 60 mmHg (some guidelines say 60–70 mmHg).
Etiology (with Focus on Hong Kong)
Organised by the Monro-Kellie components:
1. Increased Brain Volume
Cerebral oedema = excess water within the brain parenchyma. Three forms:
| Type | Mechanism | Typical cause |
|---|---|---|
| Vasogenic oedema | Disrupted BBB → protein-rich fluid leaks into extracellular space | Tumours (especially via VEGF secretion [3]), abscess, contusion, meningitis |
| Cytotoxic oedema | Cellular energy failure → loss of Na⁺/K⁺-ATPase → intracellular Na⁺/Ca²⁺ accumulation → intracellular swelling | Ischaemic stroke, hypoxia, trauma |
| Interstitial (hydrocephalic) oedema | Obstructive hydrocephalus → CSF forced trans-ependymally into periventricular extracellular space | Obstructive hydrocephalus |
In cerebral ischaemia, there is acidosis, excitotoxicity, and free radical generation leading to both cytotoxic oedema (↑ intracellular Na⁺/Ca²⁺) and vasogenic oedema (BBB disruption) [2].
Space-occupying mass lesion — e.g. haematoma, tumour, abscess [1]
| Type | Key details (HK context) |
|---|---|
| Tumours | Adults: metastases (lung, breast, colorectal — all common in HK), glioblastoma, meningioma. Children: medulloblastoma, pilocytic astrocytoma, ependymoma |
| Haematoma | EDH (middle meningeal artery tear, 90% with skull fracture), SDH (bridging vein tear; acute/subacute/chronic), ICH (hypertensive or amyloid angiopathy) |
| Abscess | Bacterial (post-otitis media, post-sinusitis, haematogenous), TB tuberculoma (HK endemic), toxoplasmosis (in HIV) |
Brain swelling — focal/diffuse [1]
Multifactorial in TBI [6]:
- Vasogenic oedema (disrupted BBB)
- Cytotoxic oedema (neuronal injury from excitotoxicity, direct injury, ischaemia)
- Reactive hyperaemia due to impaired vascular autoregulation
This creates a vicious cycle: swelling → ↑ ICP → ↓ cerebral perfusion → further neuronal injury → more swelling [6].
Hydrocephalus — communicating / non-communicating [1]
Definition: Accumulation of excess CSF within the cranium [3]
| Non-communicating (Obstructive) | Communicating | |
|---|---|---|
| Mechanism | Flow obstruction at ventricular system/aqueduct — ventricular enlargement proximal to block (4th ventricle normal if aqueduct blocked) | At arachnoid villi — all ventricles dilated including 4th ventricle |
| Acquired causes | Tumours: CPA tumours (vestibular schwannoma, meningioma), brain metastasis, gliomas, craniopharyngioma/pituitary macroadenoma; Vascular: cerebellar infarct, ICH, IVH; Infections: ventriculitis, post-infective aqueductal stenosis, brain abscess, neurocysticercosis | Tumours: leptomeningeal carcinomatosis; Vascular: SAH, IVH; Infections: basal meningitis (e.g. TB, Cryptococcal — very relevant in HK); Normal pressure hydrocephalus |
| Congenital causes | Aqueductal stenosis, Type II Chiari malformation (Arnold-Chiari), Dandy-Walker malformation [1][3] | Overproduction of CSF (rare): choroid plexus papilloma |
Some common causes of hydrocephalus [1]:
- Acquired: ↑ CSF production (e.g. choroidal plexus papilloma), flow obstruction (e.g. tumour, haematoma), ↓ absorption (e.g. meningitis, SAH), idiopathic
- Congenital: aqueductal stenosis, Arnold-Chiari malformation, Dandy-Walker syndrome, neural tube defect, congenital infection, congenital mass lesions
Hyperaemia [1] — arterial:
- Post-traumatic reactive hyperaemia (loss of autoregulation → arteriolar dilation)
- Hypercapnia (CO₂ is a potent cerebral vasodilator — ↑ PaCO₂ → ↑ CBF → ↑ ICP)
- Seizures (↑↑ metabolic demand → ↑ CBF) [7]
Venous congestion [1] — venous:
- Cerebral venous sinus thrombosis (CVST) — important in HK: F > M, associated with pregnancy, OCP use, prothrombotic states [4]
- Jugular vein compression/obstruction (e.g. tight cervical collar, neck surgery) [5]
- Impaired venous drainage from raised intrathoracic pressure (coughing, straining, Valsalva)
| Cause | Notes |
|---|---|
| Idiopathic intracranial hypertension (IIH) | Previously "benign" intracranial hypertension / pseudotumour cerebri. RFs: female, obesity, OCP, tetracycline, nalidixic acid, vitamin A, systemic steroid withdrawal [2]. Incidence 1–2/100,000/y. Unknown mechanism, possibly ↑ CSF outflow resistance + ↓ CSF reabsorption |
| Seizures | ↑ Metabolic activity → hyperaemia → ↑ ICP [5][7] |
| Craniosynostosis | Premature fusion of skull sutures → reduced cranial volume |
| Pachymeningitis | Thickened, inflamed dura → reduced compliance |
| Breakdown of BBB | Allows plasma to leak into brain → vasogenic oedema [2] |
Hong Kong-specific Aetiologies to Remember
- TB meningitis — remains endemic in HK; causes basal meningitis → communicating hydrocephalus
- Hypertensive ICH — very common given the high prevalence of hypertension in HK's ageing population
- Brain metastases — lung, breast, and colorectal carcinomas are the top 3 cancers in HK
- Falls in the elderly → SDH (chronic > acute) and contusions. Many are on anticoagulants for AF
- Nasopharyngeal carcinoma — endemic in southern China; can cause skull base invasion/venous obstruction
Pathophysiology: The Chain of Events
Let's put it all together from first principles:
Any of the above aetiologies adds volume to the fixed intracranial compartment.
Per the Monro-Kellie doctrine, CSF is displaced into the spinal canal, and venous blood is squeezed out. ICP remains relatively normal during this compensatory phase.
Once compensatory reserves are exhausted, the ICP-volume curve enters its steep (exponential) phase — even tiny additional volumes cause dramatic ICP spikes.
ICP progressively increased. Definitely abnormal > 20 cmH₂O. Suggests worsening conditions. Repeat imaging studies. Escalate treatment. [1]
↑ ICP → ↓ CPP (since CPP = MAP − ICP) → ↓ CBF → global cerebral ischaemia.
If ICP ≈ MAP → CPP ≈ 0 → brain death.
Pressure gradients across dural partitions (falx cerebri, tentorium cerebelli) drive brain tissue from a high-pressure compartment into a low-pressure one. This is brain herniation — the most feared consequence of raised ICP. (We will detail herniation syndromes under Clinical Features below.)
This is the last-ditch physiological attempt to maintain cerebral perfusion:
- ↑ ICP → ↓ CPP → brainstem ischaemia
- Brainstem ischaemia activates the vasomotor centre in the medulla → massive sympathetic discharge → systemic hypertension (to try to drive blood into the brain)
- Baroreceptors in the carotid sinus/aortic arch detect the hypertension → reflex bradycardia via vagal activation
- Brainstem respiratory centres are also affected → irregular/abnormal breathing (Cheyne-Stokes, ataxic, apnoea)
Cushing's triad = Hypertension + Bradycardia + Irregular respiration This is a late, pre-terminal sign. If you see this on a ward, it means brainstem herniation is imminent — call neurosurgery immediately.
Classification
As above — mass lesion, cerebral oedema, hydrocephalus, hyperaemia, venous congestion, IIH.
| Acute | Subacute | Chronic | |
|---|---|---|---|
| Time course | Minutes to hours | Days to weeks | Weeks to months |
| Example | Acute EDH, massive ICH | Growing tumour, subacute SDH | Chronic SDH, slow-growing tumour, NPH, IIH |
| Presentation | Rapid deterioration, herniation | Progressive headache, focal deficits | Insidious cognitive decline, gait disturbance |
- Non-communicating (obstructive): Block within the ventricular system
- Communicating: Block at the level of the arachnoid granulations or subarachnoid space
- Normal Pressure Hydrocephalus (NPH): A surgically treatable cause of cognitive decline. Complex pathophysiology of abnormal brain compliance. ICP not high despite large ventricles. [1]
Clinical Features
Clinical features depend on age, cause, chronicity, and brain compliance [1].
| Symptom | Pathophysiological basis |
|---|---|
| Headache (supine > erect; worse early a.m.) [1] | During recumbency, venous return from the brain is impeded (loss of gravitational drainage) → ↑ intracranial venous volume → ↑ ICP. Also, PaCO₂ rises slightly during sleep (hypoventilation) → cerebral vasodilation → ↑ ICP. The headache is classically diffuse, throbbing, and may worsen with coughing, straining, or bending forward (all of which ↑ intrathoracic/intra-abdominal pressure → ↑ ICP) |
| Vomiting (might transiently relieve headache) [1] | The area postrema (vomiting centre) in the floor of the 4th ventricle is directly stimulated by raised ICP. May be projectile (especially in posterior fossa lesions). Vomiting transiently ↓ ICP because the Valsalva phase ends → venous drainage improves |
| Blurring of vision [1] | Due to papilloedema (see below) causing transient visual obscurations (TVOs) — fleeting episodes of "greying out" or blurring lasting seconds, due to transient fluctuations in optic nerve head perfusion [8]. Chronic papilloedema → permanent optic nerve damage → visual field loss |
| Diplopia (CN VI) [1] | CN VI (abducens) has the longest intracranial course of any cranial nerve. It runs along the clivus, is tethered at Dorello's canal, and is therefore susceptible to stretch/compression by diffusely raised ICP. This is a false localising sign — it doesn't tell you where the lesion is, only that ICP is raised |
| Deterioration in consciousness [1] | ↓ CBF → ↓ perfusion of the ascending reticular activating system (ARAS) in the brainstem → drowsiness → stupor → coma. Also, herniation directly compresses the brainstem |
| Seizures | Focal cortical irritation from mass lesions, oedema, or ischaemia → abnormal neuronal firing. Seizures in turn cause hyperaemia and worsen ICP [7] |
| Cognitive/personality changes | Chronic raised ICP → diffuse cortical dysfunction. Common in slow-growing tumours and NPH |
Infant-specific Symptoms [1]
- Large head (macrocephaly — because sutures can separate)
- Irritability, poor feeding, failure to thrive
- Developmental delay
- "Sunset eyes" — downward deviation of the eyes due to pressure on the tectal plate (superior colliculus) → tonic downward gaze (Parinaud's syndrome variant)
| Sign | Pathophysiological basis |
|---|---|
| Papilloedema (late) [1] | ↑ ICP is transmitted along the subarachnoid space that surrounds the optic nerve sheath → acts as a "tourniquet" → ↓↓ axoplasmic outflow from the optic disc → axonal swelling → visible disc swelling on fundoscopy [8]. Signs: blurred disc margins, loss of spontaneous venous pulsation (SVP — normally present in ~80% of people), dilated superficial capillaries, haemorrhages around disc. Takes hours-days to develop, hence it is a late sign. Its absence does NOT exclude raised ICP |
| CN VI palsy | Unilateral or bilateral lateral rectus palsy → esotropia (eye turns inward) → binocular horizontal diplopia worse on looking towards the affected side. False localising sign (explained above) [8] |
| Cushing's triad (hypertension, bradycardia, irregular respiration) | Terminal sign — indicates brainstem compression (see mechanism above). Requires immediate intervention |
| Altered level of consciousness (↓ GCS) | Compression of ARAS or global hypoperfusion |
| Motor deficits [1] | Depend on the location of the lesion or herniation (see below) |
| Urinary incontinence [1] | In chronic hydrocephalus/NPH — pressure on the periventricular corticospinal fibres subserving bladder control |
| Focal neurological deficits | Mass effect → compression of specific neural structures |
Infant-specific Signs [1]
- Tense, bulging fontanelle (palpable)
- Dilated scalp veins (because venous drainage from the scalp is impeded by the tense intracranial compartment)
- Suture diastasis (palpable as widened gaps)
- ↑ Head circumference crossing centile lines
C. Herniation Syndromes
Herniation occurs when a pressure gradient drives brain tissue from one compartment to another across a rigid dural fold.
- What herniates: Cingulate gyrus under the falx cerebri
- What it compresses: Anterior cerebral artery (ACA) → contralateral leg weakness, ipsilateral ACA territory infarct
- Compression of the foramen of Monro → contralateral hydrocephalus
- What herniates: Medial temporal lobe (uncus) through the tentorial notch
- What it compresses:
- Ipsilateral CN III → ipsilateral fixed, dilated pupil (the parasympathetic fibres run on the outside of CN III and are compressed first → loss of pupillary constriction = mydriasis). This is the classic "blown pupil"
- Ipsilateral cerebral peduncle → contralateral hemiparesis (corticospinal tract decussates at the pyramids, so an ipsilateral peduncle lesion causes contralateral weakness)
- Kernohan's notch phenomenon: the contralateral cerebral peduncle is pushed against the opposite tentorial edge → ipsilateral hemiparesis (a false localising sign!)
- Posterior cerebral artery (PCA) → occipital infarct → contralateral homonymous hemianopia
- Brainstem → progressive rostro-caudal deterioration: drowsiness → coma → Cushing's reflex → death
Clinical pearl: An expanding supratentorial mass (e.g. acute EDH) classically produces: ipsilateral fixed dilated pupil → contralateral hemiparesis → progressive obtundation. This sequence reflects progressive uncal herniation.
- What herniates: Both cerebral hemispheres push downward through the tentorial notch
- Features: Bilateral fixed dilated pupils, bilateral motor signs, rapid progression to death
- Often seen with diffuse bilateral brain swelling
- What herniates: Cerebellar tonsils through the foramen magnum
- What it compresses: Medulla oblongata → cardiorespiratory arrest
- This is why lumbar puncture is contraindicated when there is raised ICP with a posterior fossa mass or significant midline shift — removing CSF from below can precipitate tonsillar herniation ("coning")
NEVER do an LP before imaging in suspected raised ICP!
If there is clinical suspicion of raised ICP, always do CT brain first before performing a lumbar puncture. Removing CSF from below a pressure gradient can precipitate fatal tonsillar herniation (coning). This is one of the most important patient safety rules in medicine.
- What herniates: Cerebellum pushed upward through the tentorial notch
- Occurs with posterior fossa masses
- Compresses the midbrain
- Brain herniates through a skull defect (fracture or craniectomy site)
- Visible as a "mushrooming" of brain tissue at the defect
A surgically treatable cause of cognitive decline.
Classic clinical triad:
- Gait disturbance — "magnetic gait" (feet appear glued to the floor), broad-based, shuffling. This is usually the first and most responsive symptom to treatment
- Cognitive decline — subcortical dementia pattern (slowed thinking, apathy, inattention)
- Urinary incontinence — initially urgency, then frank incontinence
Mnemonic: "Wet, Wacky, and Wobbly" = Incontinence, Dementia, Gait ataxia
ICP not high despite large ventricles. Complex pathophysiology of abnormal brain compliance. The current theory is that there are intermittent B-waves of raised ICP (especially at night) that cause progressive ventricular dilation, even though a single spot measurement of ICP may be normal.
Responds well to CSF diversion (e.g. VP-shunting). This is what makes it so important — it's one of the few treatable causes of dementia.
Need to distinguish from other causes of dementia such as AD, which does not respond to shunting. [1]
Herniation and ICP Monitoring Summary
- Absence of clinical monitoring (GCS < 8)
- Anticipating future deterioration
- Abnormal CT scan + no clinical monitoring (e.g. intubated, drug/alcohol intoxication)
- Normal CT scan + 2/3 risk factors (age > 40 y, SBP < 90 mmHg, uni/bilateral motor signs)
- External Ventricular Drain (EVD) — gold standard: catheter placed in lateral ventricle → allows both ICP monitoring AND therapeutic CSF drainage [7]
- Intraparenchymal probe — placed directly into brain tissue; cannot drain CSF
- Epidural/subdural sensors — less accurate
Additional Key Concepts
ICP has a pulsatile waveform synchronous with the cardiac cycle:
- P1 (percussion wave) — arterial pulsation
- P2 (tidal wave) — brain compliance
- P3 (dicrotic wave) — aortic valve closure
In normal ICP, P1 > P2. In raised ICP with reduced compliance, P2 > P1 — this is a sign that compensatory reserves are exhausted.
- A waves (plateau waves): Sustained elevations of ICP to 50–100 mmHg lasting 5–20 minutes. Pathological — indicate severely compromised intracranial compliance. Medical emergency.
- B waves: Rhythmic oscillations (0.5–2/min) of ICP up to 20–30 mmHg. Seen in reduced compliance; may be seen in NPH.
- C waves: Small (< 20 mmHg), rapid oscillations related to systemic BP changes. Generally not pathological.
High Yield Summary
-
Monro-Kellie Doctrine: Skull = rigid box. Brain (80%) + Blood (10%) + CSF (10%) = constant. ↑ in one must be offset by ↓ in others.
-
Normal ICP: Adult 10–15 mmHg, Infant 1–6 mmHg. Abnormal > 20 mmHg.
-
CPP = MAP − ICP. If ICP ↑ without ↑ MAP → CPP ↓ → CBF ↓ → ischaemia.
-
Cerebral autoregulation maintains constant CBF for MAP 50–150 mmHg normally, but is shifted right in chronic hypertension and impaired (pressure-passive) in TBI.
-
Causes (Monro-Kellie framework): ↑ Brain (oedema, mass), ↑ CSF (hydrocephalus), ↑ Blood (hyperaemia, venous congestion), Others (IIH, craniosynostosis).
-
Cerebral oedema types: Vasogenic (BBB disruption → extracellular), Cytotoxic (cell swelling → intracellular), Interstitial (obstructive hydrocephalus → periventricular).
-
Clinical features: Headache (worse supine/morning), vomiting, visual blurring, CN VI palsy (false localising), papilloedema (late), ↓ consciousness.
-
Cushing's triad (HTN + bradycardia + irregular breathing) = pre-terminal brainstem herniation sign.
-
Herniation syndromes: Subfalcine (ACA compression), Uncal (ipsilateral CN III → blown pupil, contralateral hemiparesis), Central, Tonsillar (foramen magnum → medullary death), Upward.
-
NPH = "Wet, Wacky, Wobbly" — treatable with VP shunt. Must distinguish from Alzheimer's.
-
Never LP before CT when raised ICP is suspected — risk of tonsillar herniation (coning).
-
ICP monitoring indications: GCS < 8, anticipating deterioration, abnormal CT + intubated, normal CT + 2/3 RFs.
Active Recall - Raised Intracranial Pressure
[1] Lecture slides: GC 111. Raised intracranial pressure and hydrocephalus.pdf (pp. 1–15) [2] Senior notes: Ryan Ho Neurology.pdf (pp. 153–158) [3] Senior notes: maxim.md (Intracranial tumours and hydrocephalus sections) [4] Senior notes: maxim.md (ICH and cerebral venous thrombosis sections) [5] Senior notes: felixlai.md (ICP pathophysiology and CPP sections) [6] Senior notes: Ryan Ho Neurology.pdf (p. 205, Secondary brain injury) [7] Senior notes: Ryan Ho Fundamentals.pdf (p. 339, ICP management and monitoring) [8] Senior notes: Ryan Ho Opthalmology.pdf (p. 90, Papilloedema)
Differential Diagnosis of Raised Intracranial Pressure
Raised ICP is a pathophysiological state, not a single disease. When a patient presents with features of raised ICP (headache worse supine/morning, vomiting, visual blurring, CN VI palsy, papilloedema, deteriorating consciousness), your job is to work backwards to identify the underlying aetiology — because the treatment depends entirely on the cause. A patient with a cerebellar tumour causing obstructive hydrocephalus needs emergency posterior fossa surgery, not just mannitol. A patient with IIH needs weight loss and acetazolamide, not a craniotomy.
The DDx is best organised by the Monro-Kellie framework (what component is expanded?) combined with the temporal profile (acute vs subacute vs chronic) because these two axes together narrow the differential most efficiently.
Systematic DDx Organised by Monro-Kellie Component
| Differential | Key distinguishing features | Why it causes raised ICP |
|---|---|---|
| Ischaemic stroke with cerebral oedema (malignant MCA syndrome, massive cerebellar infarct) | Acute onset focal neurological deficit (hemiplegia, aphasia, gaze deviation); CT shows hypodense territory ± midline shift after 24–72 h | Cytotoxic oedema (energy failure → intracellular swelling) ± subsequent vasogenic oedema (BBB breakdown). Peaks at 3–5 days post-stroke |
| Intracerebral haemorrhage (ICH) [4] | Acute onset headache + focal deficit + ↓GCS; NCCT shows hyperdense mass. Common sites: pons, cerebellum, putamen, thalamus (hypertensive); lobar if CAA | Direct mass effect of haematoma + surrounding oedema. Expanding haematoma ± IVH → acute hydrocephalus |
| Brain tumour [1][3] | Subacute/chronic progressive headache + focal neurological signs + seizures; often with constitutional symptoms (weight loss). Adults: 70% supratentorial (metastases, meningioma, GBM). Children 2–12 y: 70% infratentorial (medulloblastoma, pilocytic astrocytoma, ependymoma) | Tumour mass effect + vasogenic oedema (disrupted BBB, tumour-secreting VEGF) [3] ± obstructive hydrocephalus ± obstruction of cerebral venous drainage (e.g. superior sagittal sinus thrombosis) [3] |
| Brain abscess [1] | Subacute headache + fever + focal signs ± seizures; history of sinusitis, otitis media, dental infection, endocarditis, or immunocompromise; ring-enhancing lesion on CT/MRI | Expanding abscess + surrounding vasogenic oedema. Very high oedema-to-lesion ratio |
| Traumatic brain injury (TBI) — contusions, diffuse brain swelling [6] | History of trauma; NCCT shows contusions (salt-and-pepper hyperdensity within brain parenchyma), diffuse effacement of sulci/cisterns | Multifactorial: vasogenic oedema (disrupted BBB), cytotoxic oedema (neuronal injury), reactive hyperaemia (impaired autoregulation) [6] |
| Acute hypoxic-ischaemic encephalopathy | Post-cardiac arrest, near-drowning, or severe hypoxia; diffuse cerebral oedema on CT with loss of grey-white differentiation | Global energy failure → cytotoxic oedema |
| Acute hyponatraemia | Serum Na < 120 mmol/L; often iatrogenic (excessive hypotonic fluids) or SIADH. Confusion, seizures, coma | Osmotic gradient drives water into brain cells → cytotoxic oedema. The brain swells because neurons become relatively hyperosmolar to the plasma |
Hydrocephalus — communicating / non-communicating [1]
| Differential | Key distinguishing features | Mechanism |
|---|---|---|
| Obstructive (non-communicating) hydrocephalus | Acute/subacute onset depending on cause. CT shows dilated lateral and 3rd ventricles with normal-sized 4th ventricle if block at aqueduct. Causes: tumours (CPA tumours, brain metastasis, gliomas, craniopharyngioma), vascular (cerebellar infarct, ICH, IVH), infections (ventriculitis, brain abscess, neurocysticercosis), congenital (aqueductal stenosis, Chiari II, Dandy-Walker) [3] | CSF pathway blocked → CSF accumulates proximal to block → ventricular dilation → ↑ ICP |
| Communicating hydrocephalus | All ventricles dilated including 4th ventricle. Causes: SAH, IVH, basal meningitis (TB, cryptococcal — important in HK), leptomeningeal carcinomatosis [3] | Impaired CSF absorption at arachnoid granulations (post-inflammatory scarring/protein clogging) |
| Normal Pressure Hydrocephalus (NPH) [1] | Classic clinical triad: gait disturbance, cognitive decline, urinary incontinence ("Wet, Wacky, Wobbly"). ICP not high despite large ventricles. Chronic, insidious. Elderly patients | Complex pathophysiology of abnormal brain compliance. Intermittent B-waves of raised ICP cause progressive ventricular dilation. Spot ICP may be normal. Responds well to CSF diversion (e.g. VP-shunting) |
| Choroid plexus papilloma (rare) | Mostly in children < 2 y. CT shows intraventricular enhancing mass (usually lateral ventricle in children, 4th ventricle in adults) | ↑ CSF production — the papilloma actively secretes CSF at a rate exceeding normal absorption capacity |
| Differential | Key distinguishing features | Mechanism |
|---|---|---|
| Epidural haematoma (EDH) | Lucid interval then rapid deterioration; temporal bone fracture + middle meningeal artery tear (75%); lentiform hyperdense lesion on CT. Does not cross suture lines [9] | Arterial bleeding → rapidly expanding haematoma → ↑ ICP → uncal herniation |
| Subdural haematoma (SDH) — acute, subacute, chronic | Acute: post-trauma with progressive ↓GCS; crescentic hyperdense collection crossing suture lines [9]. Chronic: elderly, often on anticoagulants, vague history of minor trauma weeks ago, fluctuating confusion, focal deficits. Does not cross midline (bound by falx) | Bridging vein tear → blood accumulates between dura and arachnoid → mass effect. Chronic SDH expands through repeated micro-bleeds from neomembrane capillaries |
| Subarachnoid haemorrhage (SAH) | Thunderclap headache ("worst headache of my life"), meningism, ± ↓GCS; NCCT shows hyperdense blood in sulci/cisterns/fissures | Aneurysm rupture → blood in subarachnoid space → (1) direct mass effect/global irritation; (2) communicating hydrocephalus (blood products clog arachnoid granulations); (3) vasospasm → delayed cerebral ischaemia |
| Cerebral venous sinus thrombosis (CVST) [4] | Requires high index of suspicion. F > M (pregnancy, OCP). Headache + papilloedema + ↓GCS + seizure + focal deficits. MRI + MR venogram shows filling defect. Empty delta sign (superior sagittal sinus involvement) | Venous outflow obstruction → ↑ venous pressure → impaired CSF absorption + venous infarction ± haemorrhagic transformation |
| Reactive hyperaemia [1] | Post-TBI or post-reperfusion (e.g. after carotid endarterectomy or thrombectomy) | Loss of autoregulation → inappropriate arteriolar dilation → ↑ cerebral blood volume |
| Differential | Key distinguishing features | Mechanism |
|---|---|---|
| Bacterial meningitis | Acute onset fever, headache, neck stiffness, photophobia, ↓GCS; CSF: ↑ neutrophils, ↑ protein, ↓ glucose | Diffuse cerebral oedema (vasogenic — BBB disruption) + communicating hydrocephalus (inflammatory exudate blocks arachnoid granulations) |
| TB meningitis [10] | Subacute onset over weeks. Triphasic illness: prodromal → meningitic → paralytic. CN palsies (esp II, VI). Hydrocephalus in 80%. Basal meningeal enhancement on contrast CT/MRI | Basal exudates → communicating hydrocephalus + vasculitis → infarcts + vasogenic oedema. Very important in Hong Kong |
| Cryptococcal meningitis | Insidious onset in immunocompromised (HIV, transplant); India ink +ve, cryptococcal antigen in CSF/serum | Mucoid capsule physically blocks arachnoid granulations → communicating hydrocephalus. Also direct parenchymal invasion |
| Viral encephalitis (e.g. HSV) | Acute onset fever, confusion, seizures, temporal lobe predilection (HSV-1); MRI shows T2/FLAIR hyperintensity in temporal lobes | Cytotoxic oedema (neuronal destruction) + vasogenic oedema (BBB disruption) |
| Differential | Key distinguishing features | Mechanism |
|---|---|---|
| Idiopathic intracranial hypertension (IIH) [2] | Obese women of child-bearing age. S/S of ↑ICP: headache, transient visual loss, pulsatile tinnitus, diplopia (CN6 palsy), N/V. Papilloedema present. Imaging: normal brain parenchyma with small/normal ventricles ('slit' ventricles), enlarged sella (empty sella sign). LP: ↑ opening pressure but normal constituents | Unknown — may be ↑ CSF outflow resistance + ↓ CSF reabsorption. Diagnosis of exclusion. Must do MRV to r/o 2° ↑ICP due to CVST (which can look identical on MRI) |
| Malignant hypertension | BP ≥ 220/120 + G3–4 fundal changes (papilloedema, retinal haemorrhages, exudates); headache, confusion, visual disturbance, AKI, APO [11] | Breakthrough of cerebral autoregulation → forced vasodilation → vasogenic oedema (hypertensive encephalopathy). Important DDx for bilateral optic disc swelling, especially in the elderly [8] |
| Status epilepticus | Witnessed seizures or subtle convulsive activity; ↑ICP is secondary | Seizure → ↑↑ metabolic demand → hyperaemia → ↑ cerebral blood volume → ↑ ICP [5][7] |
| Pituitary apoplexy [12] | Sudden excruciating headache + diplopia (CN III compression) + hypopituitarism (especially adrenal crisis); known pituitary adenoma. CT/MRI: acute blood in pituitary | Sudden haemorrhage into pituitary → rapid expansion within sella → mass effect. If large enough, suprasellar extension → ↑ ICP, visual field compromise |
This is extremely useful clinically because the speed of onset immediately narrows the list [2][13]:
| Acute (minutes–hours) | Subacute (days–weeks) | Chronic (weeks–months) |
|---|---|---|
| EDH, acute SDH, ICH, SAH, massive ischaemic stroke, acute hydrocephalus, bacterial meningitis, pituitary apoplexy, acute hyponatraemia | Brain tumour, brain abscess, subacute SDH, TB meningitis, viral encephalitis, CVST, subacute hydrocephalus, IIH | Chronic SDH, slow-growing tumour, NPH, IIH, craniosynostosis, chronic meningitis |
| Infants | Children (2–12 y) | Adults | Elderly |
|---|---|---|---|
| Congenital hydrocephalus (aqueductal stenosis, Chiari II, Dandy-Walker), congenital infection (TORCH), choroid plexus papilloma, craniosynostosis, non-accidental injury (SDH + retinal haemorrhages) | Posterior fossa tumours (medulloblastoma, pilocytic astrocytoma, ependymoma) → obstructive hydrocephalus; acute disseminated encephalomyelitis (ADEM) | TBI (RTA, falls, assaults), brain metastases, GBM, meningioma, ICH, SAH, CVST, brain abscess, IIH | Chronic SDH (falls + anticoagulation + brain atrophy), hypertensive ICH, brain metastases, NPH, malignant hypertension |
When you see bilateral disc swelling, the DDx is focused [8]:
| Cause | Discriminating feature |
|---|---|
| Papilloedema (from ↑ICP) | VA usually preserved initially; only TVOs and enlarged blind spot; loss of spontaneous venous pulsation, engorged retinal veins, flame haemorrhages, CWS, exudates. Disc hyperaemic acutely, pale chronically |
| Malignant hypertension | Key DDx for bilateral disc swelling in the elderly [8]. BP ≥ 220/120 + retinal haemorrhages/exudates + signs of end-organ damage. Fundoscopy may look identical to papilloedema |
| Anterior ischaemic optic neuropathy (AION) | Almost always unilateral. Sudden visual loss with altitudinal VF defect. Pale disc (chalky-white in GCA). Spontaneous venous pulsation intact |
| Papillitis (optic neuritis) | Usually unilateral. Profound visual loss + central/paracentral scotoma + abnormal colour vision + pain on eye movement (rectus pulling on optic nerve sheath). Hyperaemic, diffusely swollen disc |
Mnemonic for disc swelling mimics (pseudopapilloedema): optic disc drusen — bilateral, elevated disc but no venous engorgement, no haemorrhages, and the disc surface is irregular/lumpy. B-scan USG or autofluorescence confirms drusen.
| Feature | Points towards... |
|---|---|
| Headache worse when supine, early morning; ↑ with coughing/sneezing; ↓ with vomiting [13] | ↑ICP of any cause |
| Headache worse when standing, promptly relieved by lying down | Intracranial hypotension (opposite of ↑ICP) — post-LP or idiopathic CSF leak [2] |
| Thunderclap headache ("worst headache of my life") | SAH until proven otherwise (also consider CVST, pituitary apoplexy, ICA dissection) [13] |
| Lucid interval after head trauma → rapid deterioration | Acute EDH (middle meningeal artery tear; the lucid interval is the compensatory phase of Monro-Kellie before decompensation) |
| Elderly on anticoagulants, fluctuating confusion, trivial/forgotten trauma weeks ago | Chronic SDH |
| Subacute onset over weeks, CN palsies (esp VI), hydrocephalus, in HK endemic area [10] | TB meningitis |
| Obese young woman + headache + visual symptoms + papilloedema + normal MRI with small ventricles + ↑ LP opening pressure with normal CSF [2] | IIH |
| Wet, Wacky, Wobbly in an elderly patient with ventriculomegaly out of proportion to atrophy [1] | NPH (surgically treatable!) |
| BP ≥ 220/120 + bilateral papilloedema + retinal haemorrhages + end-organ damage | Malignant hypertension / hypertensive encephalopathy [11] |
| Female, pregnancy/OCP, headache + seizure + focal deficit + haemorrhagic infarct pattern [4] | CVST — do MR venogram |
DDx Trap: IIH vs CVST
IIH and CVST can look almost identical clinically (young woman with headache, papilloedema, CN6 palsy) and even on standard MRI (both may show normal brain parenchyma). The critical differentiator is the MR venogram — CVST will show a filling defect / absence of flow in a dural sinus. Always do MRV to rule out secondary ↑ICP due to CVST before diagnosing IIH [2]. Missing CVST can be fatal.
DDx Trap: Papilloedema vs Malignant Hypertension
In an elderly patient with bilateral disc swelling, always check the blood pressure before assuming papilloedema from an intracranial cause. Malignant HTN is the key differential for bilateral optic disc swelling in the elderly [8]. The fundoscopic appearance can be indistinguishable from papilloedema — you need the BP and other end-organ damage to differentiate.
High Yield Summary
-
Organise DDx by Monro-Kellie component: ↑ Brain (oedema, mass, abscess, TBI), ↑ CSF (hydrocephalus — obstructive vs communicating vs NPH), ↑ Blood (EDH, SDH, SAH, CVST, hyperaemia), Others (IIH, malignant HTN, seizures).
-
Temporal profile narrows DDx fast: Acute (EDH, ICH, SAH, acute hydrocephalus, bacterial meningitis) vs Subacute (tumour, abscess, TB meningitis, CVST, subacute SDH) vs Chronic (chronic SDH, NPH, IIH, slow tumour).
-
Age-specific: Infants — congenital hydrocephalus, craniosynostosis, NAI. Children — posterior fossa tumours. Adults — TBI, tumours, ICH, IIH. Elderly — chronic SDH, NPH, hypertensive ICH, malignant HTN.
-
IIH vs CVST: Always do MR venogram. IIH is a diagnosis of exclusion. CVST = filling defect on MRV.
-
Papilloedema DDx: True papilloedema (↑ICP) vs malignant HTN (check BP!) vs papillitis (visual loss + pain on eye movement) vs AION (unilateral, altitudinal VF defect) vs pseudopapilloedema (drusen).
-
HK-specific high yield: TB meningitis (subacute, basal enhancement, hydrocephalus in 80%), hypertensive ICH (putamen/thalamus/pons/cerebellum), brain metastases (lung/breast/colorectal), chronic SDH (elderly on anticoagulants), NPC skull base invasion.
Active Recall - DDx of Raised ICP
References
[1] Lecture slides: GC 111. Raised intracranial pressure and hydrocephalus.pdf (pp. 2, 8–9, 14–15) [2] Senior notes: Ryan Ho Neurology.pdf (pp. 155, 158) [3] Senior notes: maxim.md (Intracranial tumours, hydrocephalus, and ICH sections) [4] Senior notes: maxim.md (ICH and cerebral venous thrombosis sections) [5] Senior notes: felixlai.md (ICP causes and pathophysiology sections) [6] Senior notes: Ryan Ho Neurology.pdf (p. 205, Secondary brain injury) [7] Senior notes: Ryan Ho Fundamentals.pdf (p. 339) [8] Senior notes: Ryan Ho Opthalmology.pdf (pp. 85, 88, 90) [9] Senior notes: Ryan Ho Diagnostic Radiology.pdf (pp. 41–42) [10] Senior notes: Ryan Ho Respiratory.pdf (p. 79) [11] Senior notes: Ryan Ho Cardiology.pdf (p. 182) [12] Senior notes: Ryan Ho Endocrine.pdf (p. 107) [13] Senior notes: Ryan Ho Fundamentals.pdf (pp. 312–315)
Diagnostic Criteria for Raised ICP
Raised ICP is fundamentally a pathophysiological state, not a stand-alone diagnosis with a single set of diagnostic criteria the way, say, rheumatoid arthritis has ACR/EULAR criteria. Instead, the "diagnosis" involves two parallel tracks:
- Recognising that ICP is elevated (clinical features ± direct measurement)
- Identifying the underlying cause (neuroimaging ± LP ± targeted investigations)
There is, however, one condition — Idiopathic Intracranial Hypertension (IIH) — that does have formal diagnostic criteria because it is a diagnosis of exclusion where you need to prove the ICP is elevated AND that no structural cause exists.
| Parameter | Value | Clinical significance |
|---|---|---|
| Normal adult ICP | 10–15 mmHg [1][2] | Measured at level of external auditory meatus (approximates foramen of Monro) |
| Normal infant ICP | 1–6 mmHg [1] | Lower because open fontanelles provide compliance |
| Normal young children ICP | 3–7 mmHg [2][5] | |
| Intracranial hypertension threshold | ≥ 20 mmHg (≈ 20 cmH₂O) [1][5] | Definitely abnormal > 20 cmH₂O [1]. This is the threshold to intervene in most protocols (Brain Trauma Foundation 4th edition recommends treating ICP > 22 mmHg in TBI) |
| Severe intracranial hypertension | > 25–30 mmHg | Aggressive escalation needed; risk of herniation imminent |
| Refractory intracranial hypertension | ICP > 25 mmHg for > 25 min/h or > 30 min in any 1 hour despite maximal tier 1–2 therapy | Consider decompressive craniectomy or barbiturate coma |
Why 20 cmH₂O / ~15 mmHg? Because above this level, the ICP-volume curve has entered its steep (decompensated) phase, and even small further volume additions cause dramatic ICP spikes. The Brain Trauma Foundation (4th edition, 2016; reaffirmed 2020) chose 22 mmHg as the treatment threshold based on observational data showing worse outcomes above this level.
Since IIH is a diagnosis of exclusion, formal criteria exist [2][8]:
| Criterion | Explanation |
|---|---|
| 1. Signs and symptoms of raised ICP (headache, papilloedema, TVOs, CN6 palsy, tinnitus) | Must have clinical features attributable to raised ICP — papilloedema is the hallmark |
| 2. Normal neurological examination except for CN6 palsy | Any other focal deficit suggests a structural cause |
| 3. Normal brain parenchyma on MRI with small or normal ventricles ("slit ventricles") | Rules out mass lesions, hydrocephalus. May show enlarged sella filled with CSF (empty sella sign) [2] |
| 4. Normal CSF composition on LP | Rules out meningitis, carcinomatosis |
| 5. Elevated LP opening pressure: > 25 cmH₂O in adults (> 28 cmH₂O in children) | The defining feature — proves that ICP is actually elevated |
| 6. No other identifiable cause, including MR venogram to rule out CVST [2] | CVST can mimic IIH perfectly on standard MRI |
IIH: Diagnosis of Exclusion
You cannot diagnose IIH without ruling out CVST with MR venography. Both conditions cause raised ICP with normal brain parenchyma on standard MRI. Missing CVST (which requires anticoagulation) can be fatal. ± MRV to r/o 2° ↑ICP due to CVST (otherwise similar appearance on MRI) [2].
The approach follows a logical sequence: clinical suspicion → emergency stabilisation → neuroimaging → ± LP → targeted investigations for the cause.
Key Decision Points Explained
Why CT first, not MRI?
- CT is fast (1 minute) [14], widely available 24/7, and excellent at detecting acute blood (hyperdense on NCCT), mass effect/midline shift, and hydrocephalus — the three things you need to know immediately. MRI takes ~20 min, is not always available urgently, and is harder to perform on unstable patients.
Why not LP first?
- LP contraindicated if raised ICP [1] (with exceptions, e.g. communicating hydrocephalus from meningitis where the benefit outweighs the risk). Removing CSF from below a pressure gradient can precipitate tonsillar herniation (coning). You must image first to confirm there is no mass effect or obstructive hydrocephalus.
CT/MRI brain + no papilloedema before LP if suspect mass lesion or ↑ICP. Indications for imaging before LP: altered consciousness, focal signs, papilloedema, seizure, immunocompromised [15].
When to add MRI + MR venogram?
- When CT is non-diagnostic or normal but clinical suspicion remains high
- When you suspect CVST [4] (young woman, prothrombotic state, headache + seizure + focal deficit)
- When you suspect IIH [2] (need MRV to exclude CVST)
- For IIH: MRI and MR venogram + Lumbar puncture [13]
Investigation Modalities: Key Findings & Interpretations
NECT brain: single most important investigation in head injury [7] and the first-line investigation for suspected raised ICP in any acute setting.
Why non-contrast specifically? Because contrast can obscure blood (both appear hyperdense). You want to see blood first.
| Finding | Interpretation | Underlying cause |
|---|---|---|
| Lentiform hyperdense collection not crossing suture lines [9] | Acute epidural haematoma (EDH) | Middle meningeal artery tear (75%); 90% associated with skull fracture |
| Crescentic hyperdense collection crossing suture lines but not midline [9] | Acute subdural haematoma (SDH) | Bridging vein tear. Subacute SDH is isodense (difficult to see — should do CT ASAP after injury, or contrast CT [9]). Chronic SDH is hypodense |
| Hyperdense mass within brain parenchyma | Intracerebral haemorrhage (ICH) | Urgent NCCT brain: size and location of haematoma, any IVH/hydrocephalus, any mass effect [4] |
| Hyperdense blood in sulci/cisterns/Sylvian fissure | Subarachnoid haemorrhage (SAH) | Sensitivity ~95% within 6 h, drops to ~50% by day 5. If -ve but clinical suspicion high → LP for xanthochromia |
| Dilated ventricles (lateral + 3rd but NOT 4th) | Obstructive hydrocephalus at aqueductal level | Look for cause at the level of obstruction (tumour, clot) |
| Dilated ALL ventricles including 4th | Communicating hydrocephalus | Post-SAH, post-meningitis, leptomeningeal carcinomatosis |
| Diffuse sulcal effacement, loss of grey-white differentiation, compressed basal cisterns | Diffuse cerebral oedema | TBI, hypoxic-ischaemic encephalopathy, acute hyponatraemia, meningoencephalitis |
| Midline shift (> 5 mm is significant) | Mass effect from unilateral lesion | Indicates herniation risk — urgent neurosurgical consultation |
| Hypodense area in vascular territory with mass effect | Large territory ischaemic stroke with oedema | Peaks at 3–5 days; early signs: dense MCA sign, loss of insular ribbon [14] |
| Ring-enhancing lesion (on contrast CT) | Brain abscess or tumour (GBM) | Abscess: restricted diffusion on DWI-MRI (cellular pus restricts water movement). GBM: facilitated diffusion |
| Erosion of posterior clinoids on bone window [16] | Chronic raised ICP | Long-standing pressure remodels the sella — a subtle but classic sign |
CT Appearance of Blood Over Time
| Phase | Timing | CT appearance | Why? |
|---|---|---|---|
| Acute | < 1 week | Hyperdense | Fresh clot has high haemoglobin concentration → high attenuation |
| Subacute | 1–3 weeks | Isodense | Haemoglobin degradation → attenuation falls toward brain density. Difficult to visualise — this is the dangerous "invisible" period |
| Chronic | > 3 weeks | Hypodense (≈ CSF density) | Almost all protein degraded [9] |
The Isodense Trap
A subacute SDH (1–3 weeks old) can be isodense to brain and easily missed on NCCT. If clinical suspicion is high (elderly patient, progressive confusion, anticoagulants), consider contrast-enhanced CT (the neomembranes will enhance) or MRI (much more sensitive for subacute collections). Isodense: difficult to visualize → should do CT ASAP after injury (or do contrast CT instead) [9].
MRI: more sensitive than CT especially in the first few hours for ischaemic stroke and many other conditions [14]. Generally preferred over CT for characterising intracranial tumours, infections, and oedema.
| MRI Sequence | What it shows | Key findings in raised ICP |
|---|---|---|
| T1-weighted | Anatomy (CSF dark, fat bright) | Subacute blood is T1 bright (methaemoglobin). Mass effect. Tonsillar herniation (low-lying tonsils) |
| T2-weighted / FLAIR | Oedema (CSF bright on T2, suppressed on FLAIR) | Vasogenic oedema most apparent on FLAIR MRI [3]. Periventricular transependymal CSF flow in hydrocephalus |
| DWI / ADC | Restricted vs facilitated diffusion | Cytotoxic oedema = restricted diffusion (early ischaemic stroke within minutes [14]). Abscess = restricted diffusion. Tumour cyst = facilitated diffusion [3] — key differentiator |
| SWI / GRE | Blood products (haemosiderin) | Microbleeds in cerebral amyloid angiopathy, diffuse axonal injury (small dark dots at grey-white junction, corpus callosum) |
| Gadolinium contrast | BBB disruption | Normal brain tissue does not enhance (due to BBB). Enhancement indicates: outside BBB (e.g. meningioma — homogeneous), or disruption of BBB (e.g. high-grade tumours, stroke, inflammation) [15]. Ring-enhancing: abscess or GBM |
| MR Spectroscopy | Metabolite ratios | ↑ Choline/NAA ratio in tumours (high cell turnover); lactate peak in abscess |
| MR Perfusion | Cerebral blood flow maps | High-grade tumours show ↑ perfusion; low-grade show ↓ perfusion |
Specific MRI Findings by Condition
| Condition | MRI findings |
|---|---|
| IIH | Normal brain parenchyma, small or normal ventricles ("slit ventricles"), enlarged sella filled with CSF (empty sella sign) [2]. ± flattened posterior sclera, perioptic CSF distension, vertical tortuosity of optic nerve |
| CVST | MRI brain + MR venogram for filling defect. Empty delta sign (superior sagittal sinus involvement) [4]. May also see venous infarcts (often haemorrhagic, not conforming to arterial territory) |
| TB meningitis | Basal meningeal enhancement and exudate, tuberculoma, hydrocephalus, periventricular infarcts [10] |
| HSV encephalitis | T2/FLAIR hyperintensity in medial temporal lobes (classically asymmetric), ± haemorrhagic change on SWI |
| Brain metastases | Multiple lesions at grey-white junction, circumscribed margins, large volume of vasogenic oedema compared to size of lesion [15] |
| Intracranial hypotension | Diffuse pachymeningeal enhancement (due to ↑ blood volume — compensatory venous engorgement), dilated veins, sagging brain ± pocket of CSF at site of leakage [2] |
- Specifically for diagnosing or excluding CVST
- Shows filling defects in dural venous sinuses
- Must be performed before diagnosing IIH to exclude secondary cause of raised ICP [2]
| Modality | When to use | Key findings |
|---|---|---|
| CTA | SAH (to locate aneurysm), suspected vascular malformation, non-hypertensive ICH. Indications for vascular imaging: no HTN, age < 40–45, atypical location, CT abnormality (mass, calcifications) [4] | Berry aneurysm, AVM nidus, Moya-Moya pattern |
| DSA | Gold standard for cerebrovascular anatomy; used when CTA equivocal or for pre-intervention planning | Detailed vascular anatomy, vasospasm in SAH |
LP contraindicated if raised ICP (with exception…) [1]. The exception is communicating hydrocephalus from meningitis, where there is no focal mass to cause herniation, and the diagnostic yield (CSF analysis) outweighs the risk.
| Parameter | Normal | Finding in raised ICP | Interpretation |
|---|---|---|---|
| Opening pressure | 6–20 cmH₂O | > 20–25 cmH₂O | Confirms raised ICP. IIH: LP opening pressure elevated but normal constituents [2] |
| Appearance | Clear, colourless | Turbid = infection; yellow (xanthochromia) = SAH > 12 h; blood-tinged = traumatic tap vs SAH | Xanthochromia = bilirubin from degraded Hb → confirms blood was in CSF for > 12 h (not a traumatic tap) |
| Protein | < 0.45 g/L | ↑ 1–5 g/L in TB meningitis [10]; moderately ↑ in bacterial; mildly ↑ in viral | High protein = BBB disruption or intrathecal immunoglobulin production |
| Glucose | > 50–60% of serum glucose | ↓ glucose (< 2.5 mmol/L) in TB meningitis [10]; very low in bacterial; normal in viral | Consumed by bacteria/neutrophils/mycobacteria |
| Cell count | < 5 WBC/µL, no RBC | Neutrophilic in acute bacterial; lymphocytic pleocytosis (100–500/µL) in TB [10]; lymphocytic in viral | Pattern guides empirical therapy |
| Microbiology | Sterile | AFB smear (sens 30–60%), culture (sens up to 80%), TB-PCR (sens 82%, spec 99%) [10]; Gram stain, culture; Indian ink (+ve in cryptococcal), cryptococcal Ag [15] |
Indications for imaging before LP (to rule out mass lesion/raised ICP): altered consciousness, focal signs, papilloedema, seizure, immunocompromised [15].
- No reliable GCS (e.g. sedation, muscle paralysis) [1]
- GCS ≤ 8 (requires intubation) [1]
- Evolving disease conditions [1]
Relative contraindications: awake patients; bleeding tendency [2].
| Method | Principle | Advantages | Disadvantages |
|---|---|---|---|
| External Ventricular Drain (EVD) [1][2][5] | Catheter in lateral ventricle connected to pressure transducer + drainage system | GOLD STANDARD [5]. Manometric principle for monitoring intracranial CSF pressure. Therapeutic by draining CSF for decompression [1]. Allows CSF sampling | Risk of infection, iatrogenic trauma [1]. Requires neurosurgical placement |
| Intraparenchymal probe (e.g. Codman, Camino) | Fibre-optic or strain-gauge probe placed into brain tissue | Easier to place; lower infection risk than EVD | Cannot drain CSF; cannot recalibrate in situ (drift over days) |
| Epidural/subdural sensors | Placed in epidural or subdural space | Less invasive | Less accurate; less commonly used |
Interpretation of ICP monitoring [1][2]:
- Normal = 5–15 cmH₂O in adults
- Definitely abnormal if > 20 cmH₂O → suggests evolving pathology → repeat imaging studies or escalate treatment [1][2]
Clinical application example from lecture [1]: Initial GCS = E1M4V2. Intubated, ventilated & observed. ICP progressively increased from 16 to 28 cmH₂O. Definitely abnormal > 20 cmH₂O. Suggests worsening conditions. Repeat imaging studies. Escalate treatment.
- Bedside investigation — should be performed on every patient with suspected raised ICP
- Looking for papilloedema (see clinical features section for detailed findings) [8]
- Fundus: swollen optic disc with blurred edges, dilated superficial capillaries and NO spontaneous venous pulsation of CRV [8]
- VF: enlarged blind spot (acute), constricted VF (chronic) [8]
- Remember: papilloedema is a LATE feature [1] — its absence does NOT exclude raised ICP
| Investigation | When to order | What to look for |
|---|---|---|
| Bloods: FBC, CRP/ESR, coagulation, U&E, glucose, blood cultures | All patients | ↑ WCC/CRP (infection); coagulopathy (anticoagulant-related bleed); hyponatraemia (SIADH from ↑ICP [17]); blood cultures (meningitis) |
| Serum Na⁺ and osmolality | Any CNS pathology | SIADH (euvolaemic hypoNa with inappropriately concentrated urine) vs CSWS (hypovolaemic hypoNa) — both complicate ↑ICP [17] |
| CT C-spine | Trauma | Watch out for cervical spine injury — concurrent in up to 5–10% of severe TBI [4] |
| CXR | Trauma, suspected TB, suspected lung primary | TB meningitis: CXR for underlying pTB [10]. Brain metastases: primary lung tumour |
| Skull X-ray | Rarely used now; historical | Erosion of posterior clinoids = chronic ↑ICP [16]. Fracture lines. Calcified tumours (craniopharyngioma). Seldom done nowadays due to low sensitivity and specificity [16] |
| EEG | Seizures, status epilepticus, encephalitis | Diffuse slowing (encephalopathy), periodic lateralising epileptiform discharges (HSV encephalitis), non-convulsive status |
| Stereotactic biopsy | Brain tumour where histological diagnosis needed and surgical resection not immediately planned [3] | Tumour grading, molecular markers (IDH mutation, MGMT methylation in gliomas) |
| Transcranial Doppler (TCD) | Non-invasive estimation of ICP; monitoring vasospasm in SAH | Pulsatility index > 1.2–1.4 suggests raised ICP. ↑ systolic velocity in vasospasm |
| Scenario | First-line | Second-line | Targeted |
|---|---|---|---|
| Acute head trauma | NECT brain [7] + CT C-spine | ICP monitoring if GCS ≤ 8 | CTA if vascular injury suspected |
| Acute non-traumatic headache ± ↓GCS | NECT brain (r/o haemorrhage) | LP if SAH suspected but CT -ve | CTA/DSA for aneurysm |
| Subacute headache + focal signs | NECT brain → contrast CT or MRI | MRI + contrast for tumour/abscess | Stereotactic biopsy for tumour |
| Suspected meningitis | CT/MRI before LP if altered consciousness, focal signs, papilloedema, seizure, immunocompromised [15] | LP + CSF analysis | Blood cultures, CXR, specific PCR |
| Suspected IIH | MRI + MR venogram [2][13] | LP with opening pressure + CSF analysis | Visual field testing, OCT of RNFL |
| Suspected CVST | CT brain (may be normal) → MRI + MRV [4] | ± CT venogram if MRI unavailable | Thrombophilia screen, pregnancy test |
| Infant with large head | Transfontanelle USS (non-invasive, no radiation) → MRI | CT if urgent/USS equivocal | Genetic testing if congenital cause |
High Yield Summary
-
Raised ICP threshold: ≥ 20 mmHg (definitely abnormal > 20 cmH₂O). Brain Trauma Foundation treats > 22 mmHg in TBI.
-
IIH diagnostic criteria (Modified Dandy): Signs of raised ICP + normal neuro exam (except CN6) + normal MRI brain + normal MRV (exclude CVST!) + normal CSF composition + elevated LP opening pressure > 25 cmH₂O.
-
Investigation sequence: Clinical suspicion → ABCDE → Urgent NECT brain → ± MRI/MRV → ± LP (only after imaging rules out mass lesion) → Targeted investigations.
-
NECT brain = first-line for acute raised ICP (fast, available, detects blood/mass/hydrocephalus/shift).
-
MRI superior for tumour characterisation, abscess vs tumour (DWI), oedema (FLAIR), IIH (empty sella, slit ventricles), CVST (MRV), intracranial hypotension (pachymeningeal enhancement).
-
EVD = gold standard for ICP monitoring. Indications: GCS ≤ 8, no reliable clinical monitoring, evolving conditions.
-
LP contraindicated if raised ICP with mass lesion. Always image first. Exception: suspected meningitis with communicating hydrocephalus (no mass effect).
-
CT blood appearance changes with time: Acute = hyperdense, Subacute = isodense (danger zone — easy to miss), Chronic = hypodense.
Active Recall - Diagnosis of Raised ICP
[1] Lecture slides: GC 111. Raised intracranial pressure and hydrocephalus.pdf (pp. 1–2, 8–9) [2] Senior notes: Ryan Ho Neurology.pdf (pp. 153, 156, 158) [3] Senior notes: maxim.md (Intracranial tumours and hydrocephalus sections) [4] Senior notes: maxim.md (ICH and cerebral venous thrombosis sections) [5] Senior notes: felixlai.md (ICP overview and monitoring sections) [7] Senior notes: Ryan Ho Fundamentals.pdf (p. 337) [8] Senior notes: Ryan Ho Opthalmology.pdf (pp. 88, 90) [9] Senior notes: Ryan Ho Diagnostic Radiology.pdf (pp. 40–42, 50) [10] Senior notes: Ryan Ho Respiratory.pdf (p. 79) [13] Senior notes: Ryan Ho Fundamentals.pdf (p. 315) [14] Senior notes: Ryan Ho Diagnostic Radiology.pdf (pp. 40, 50) [15] Senior notes: Ryan Ho Neurology.pdf (pp. 145, 149, 162, 164) [16] Senior notes: Ryan Ho Neurology.pdf (p. 32) [17] Senior notes: Ryan Ho Urogenital.pdf (p. 17)
Management of Raised Intracranial Pressure
Before diving into individual treatments, you need to understand the philosophy of managing raised ICP. The lecture slides summarise it best:
The Fundamentals: [1]
- Protect uninjured brain
- Salvage injured brain
- Treat underlying cause
- ALWAYS resuscitate first
- Clinical/ICP monitoring
- Control ICP & maintain cerebral perfusion
- Neuroprotective therapies
The single most important concept: ABC before ICP !! [1]. Why? Because maintaining normal ICP is pointless if the patient has no airway, no oxygenation, or no blood pressure. Even with normal ICP, a hypoxaemic or hypotensive brain will become ischaemic. You must ensure adequate oxygen delivery (airway + breathing) and cerebral perfusion pressure (circulation) before anything else.
Treatment targets (primarily from TBI guidelines, but applicable broadly) [18]:
- ICP < 22 mmHg (Brain Trauma Foundation 4th edition, 2016)
- CPP 60–70 mmHg
- SpO₂ > 97%, PaO₂ > 9 kPa
- PaCO₂ 4.5–5 kPa (normocapnia; avoid routine hyperventilation)
- Temperature < 37°C, avoid hypoglycaemia
- Serum Na > 140 mmol/L
Detailed Treatment Modalities
Treatment by Any Doctor (Tier 0 — General Measures)
Treatment of Raised ICP — By any doctor: [1]
- Head elevation
- Optimise ventilation
- Maintain MAP
- Osmotherapy
- Sedation
- Optimise electrolyte/glucose level
- Prevent/Control seizure
- Prevent pyrexia
| Component | Action | Rationale |
|---|---|---|
| Airway | Intubation to maintain airway patency and prevent aspiration [5] | GCS ≤ 8 → patient cannot protect own airway. Aspiration → pneumonia → hypoxaemia → ↑ ICP. Intubation also allows controlled ventilation |
| Breathing | Maintain SpO₂ > 97%, PaO₂ > 9 kPa [18]. Avoid hypoxaemia at all costs | Hypoxaemia causes reflex cerebral vasodilation → ↑ cerebral blood volume → ↑ ICP. Also directly causes neuronal injury |
| Circulation | Maintain MAP to keep CPP ≥ 60 mmHg [1][5]. Avoid hypotension. Maintain vascular volume & BP [1] | CPP = MAP − ICP. If MAP drops, CPP drops → cerebral ischaemia. In TBI, autoregulation is impaired (pressure-passive system), so the brain is entirely dependent on systemic BP. Hypotension with hypoxemia induces reactive vasodilation and elevation in ICP [5]. BP should only be treated when CPP > 120 mmHg or ICP > 20 mmHg [5] |
| Disability | GCS assessment (post-resuscitation), pupil examination | Baseline neurological status for monitoring |
| Exposure | Temperature, full body survey for associated injuries | Polytrauma common in TBI |
Critical Safety Points
Do NOT: [7]
- Give mannitol if shocked — mannitol causes osmotic diuresis → ↓ intravascular volume → worsens shock → ↓ CPP
- Blindly hyperventilate (PaCO₂ 30–35 mmHg) — can lead to vasoconstriction and may exacerbate ischaemia
- Use barbiturate/propofol outside ICU — risk of cardiovascular collapse without monitoring
- Give steroids (not effective for TBI, contraindicated) — CRASH trial showed ↑ mortality with high-dose methylprednisolone in TBI
Enhanced Cerebral Venous Drainage: [1]
- Avoid neck rotation
- Remove neck collar if not indicated
- Head elevation ~30°
- Maintain vascular volume & BP
Why head up 30°? [5]
- Optimises jugular venous drainage by gravity → ↓ intracranial venous volume → ↓ ICP
- The effect on CPP is a balance: head elevation ↓ JVP (good for ICP), but also slightly ↓ MAP at the level of the head (potentially bad for CPP)
- At 30°, the net effect is beneficial: ↓ ICP outweighs any ↓ MAP → CPP improves
- Over-elevation (e.g. sitting bolt upright) will compromise carotid arterial flow and leads to an overall decrease in CPP [5]
- Neck rotation/flexion kinks the internal jugular veins → impedes venous drainage → ↑ ICP. This is why you should loosen cervical collars if not needed and NEVER put in jugular line in a patient with ↑ICP — opt for subclavian or femoral routes instead [2]
- Purpose: Reduces metabolic demand, ventilatory asynchrony, venous congestion (from straining/coughing), and sympathetic response of hypertension and tachycardia [5]
- Propofol is commonly used due to short half-life and easy titration [5]. Can be switched off quickly for neurological assessment ("sedation hold")
- Midazolam is an alternative (longer acting)
- Fentanyl/remifentanil for analgesia — pain itself causes sympathetic activation → ↑ BP → can ↑ ICP
- Sedation renders GCS unreliable (the patient is iatrogenically GCS 3) → this is why ICP monitoring is needed when patients are sedated [2]
- Patients should be kept euvolemic and normo-osmolar [5]
- Avoid hypotonic fluids (e.g. D5W, 0.45% NaCl) — these lower serum osmolality → water moves into the brain → worsens oedema
- Preferred fluids: Normal saline (0.9% NaCl) or Hartmann's solution
- Hyponatraemia is common in raised ICP, particularly in SAH [5] (due to SIADH or cerebral salt wasting [17])
- Serum Na target > 140 mmol/L [18]
- Prevent/Control seizure [1]
- Seizure can cause hyperemia and exacerbate ↑ICP [7]
- Seizure prophylaxis for 1 week only (if seizure history present or diffuse cortical damage) [7][18]
- Anti-epileptic drugs: usually levetiracetam (Keppra) or phenytoin
- Indicated if seizures are suspected and prophylaxis for supratentorial lesions [5]
- NOT recommended for infratentorial lesions [5] — the cerebellar cortex is inhibitory in nature, so seizures don't arise from infratentorial structures [15]
- Prolonged prophylaxis (> 7 days) does not reduce late post-traumatic epilepsy and has side effects
- Optimise electrolyte/glucose level [1]
- Hyperglycaemia worsens ischaemic brain injury (increases anaerobic metabolism → lactic acidosis → more oedema). Target glucose 6–10 mmol/L with insulin sliding scale
- Hypoglycaemia is directly neurotoxic — must be avoided absolutely
- Correct hyponatraemia (common — see SIADH/CSWS discussion)
First-Tier Medical Therapy (Tier 1)
8. Osmotherapy
The two agents used are IV mannitol and hypertonic saline. Both work by creating an osmotic gradient across an intact BBB, drawing water from the brain's extracellular space into the intravascular compartment.
Mannitol: onset 15 min, DoA 6 h, bolus 0.25–1 g/kg, must put in Foley [7]
| Property | Detail |
|---|---|
| Mechanism | (1) ↑ Osmotic gradient between cerebral tissue and blood vessel → ↓ oedema. (2) ↑ Deformability of RBCs → improve rheology → better cerebral perfusion. (3) Osmotic diuresis → ↓ blood volume (→ ↓ ICP) [2] |
| Dose | 0.25–1 g/kg IV bolus (typically 20% mannitol = 1 g/5 mL). Can repeat Q4–6H |
| Onset | 15 minutes |
| Duration | ~6 hours |
| Monitoring | Foley catheter mandatory (large urine volumes; risk of bladder distension/rupture). Serum Na, osmolality, renal function |
| Precautions | Mannitol is also an immediate plasma expander before powerful diuresis → ↑↑ cardiac workload [2] |
| Contraindications | Avoid if hyperNa, osmolarity > 320–340, hypovolaemia, HF [7]. Avoid in patients with renal failure (risk of acute tubular necrosis) [5]. Do NOT give mannitol if shocked [7] |
| Limitations | Equilibrium reached in ~1 week → no longer effective. Must be tapered (not stopped abruptly) to prevent sudden reversal of osmotic gradient (rebound oedema) [2] |
- Alternative to mannitol, increasingly preferred in many centres
- Concentrations: 3%, 5%, 7.5%, or up to 23.4% (the latter usually given via central line only)
- Advantages over mannitol: Does not cause osmotic diuresis (so maintains intravascular volume → safer in shocked patients), no renal toxicity
- If in shock, can consider using hypertonic saline (up to 23.4%) instead [2]
- Mechanism: Same osmotic principle as mannitol. Also has additional theoretical anti-inflammatory and rheological benefits
- Target serum Na: 145–155 mmol/L (do not exceed ~160 mmol/L)
By neurosurgeon/ICU: Controlled hyperventilation [1]
| Property | Detail |
|---|---|
| Mechanism | ↓ PaCO₂ → respiratory alkalosis → cerebral arteriolar vasoconstriction → ↓ cerebral blood volume → ↓ ICP [2][5] |
| Target | PaCO₂ 30–35 mmHg (3.0–3.5 kPa) [5][7]. Aim for low-normal (normocapnia to mild hypocapnia) |
| Onset | Rapid onset (~1 minute) [7] — this makes it an excellent emergency temporising measure |
| Duration | Short-term only — should be tapered back to normal over several hours to avoid rebound vasodilatation [5] |
| Indications | Emergency temporisation while preparing for definitive treatment (e.g. surgery). Acute deterioration with signs of herniation |
| Precautions | Excessive vasoconstriction → ↑ CVR → ↓ CBF (undesirable) [5]. Blindly hyperventilating can exacerbate ischaemia [7]. Not recommended for first 24 h of head injury (when CBF is already low) [7]. Risk of rebound ↑ ICP when hyperventilation is discontinued abruptly |
From first principles: CO₂ crosses the BBB freely. When PaCO₂ drops, perivascular pH rises (more alkaline). This alkalosis causes smooth muscle constriction in cerebral arterioles → ↓ arteriolar diameter → ↓ cerebral blood volume → ↓ ICP. But over 24–48 h, CSF bicarbonate is renally adjusted to normalise perivascular pH → the vasoconstriction wears off. That's why hyperventilation is only a temporising measure.
| Property | Detail |
|---|---|
| Mechanism | Reduces vasogenic oedema by stabilising the BBB (↓ capillary permeability, ↓ VEGF expression) [2] |
| Indication | Only effective in vasogenic oedema → therefore, only useful in tumour-related oedema [2]. Also used in CNS infections (bacterial meningitis — dexamethasone before antibiotics; brain abscess) [5] |
| Dose | PO or IV dexamethasone 10 mg stat then 4 mg Q4–6H (or 8 mg BD) [15] |
| Contraindications | NOT used for trauma (CRASH trial: ↑ acute mortality) [7]. NOT used for stroke (proven worse outcome) [2]. NOT useful in ↑ICP due to acute liver failure [19]. C/I in suspected CNS lymphoma (steroid causes acute lysis of lymphocytes → ↓ diagnostic yield on biopsy) [15] |
Steroids: Know When to Use and When NOT to Use
Steroids are wonderful for tumour-associated vasogenic oedema — a patient with a GBM and surrounding oedema can dramatically improve within hours of dexamethasone. But they are harmful in TBI (CRASH trial) and stroke. This is a frequently tested distinction.
Second-Tier Medical Therapy (Tier 2 — Refractory ICP)
By neurosurgeon/ICU: [1]
- ICP monitoring + CSF drainage
- Controlled hyperventilation
- Barbiturate coma
- Surgical removal of SOL
- Decompressive craniectomy
| Property | Detail |
|---|---|
| Agents | Pentobarbital, thiopentone |
| Mechanism | ↓ Neuronal activity → ↓ cerebral metabolic rate (metabolic coupling) → ↓ cerebral blood flow → ↓ ICP [2][5]. Also: alteration in vascular tone + inhibition of free radical-mediated lipid peroxidation [5] |
| Indication | Last-resort pharmacological option for refractory ↑ ICP unresponsive to first-tier therapy |
| Monitoring | Requires 1-lead EEG (aim for burst suppression pattern — beyond this, no further ICP benefit) [2]. Requires invasive haemodynamic monitoring |
| Risks | Risk of ↓BP, infection, electrolyte problems [7]. Hypotension and myocardial depression [2]. Must be in ICU [7] |
| Notes | RARELY done in clinical practice [2] |
| Property | Detail |
|---|---|
| Mechanism | Reduces brain metabolism → ↓ demand for CBF → ↓ ICP [5] |
| Target | 32–35°C (mild-moderate hypothermia) |
| Evidence | Therapeutic hypothermia is not recommended in adults (no benefit in RCTs) but less certain in children [7] |
| Risks | Cardiac arrest, ischaemia, bleeding tendency, pneumonia [7]. Also coagulopathy and shivering (which paradoxically ↑ metabolic rate) [2] |
Neurosurgical Interventions (Tier 3)
External Ventricular Drain: [1]
- Manometric principle for monitoring intracranial CSF pressure
- Therapeutic by draining CSF for decompression
- Risk of infection, iatrogenic trauma
| Property | Detail |
|---|---|
| Indication | Hydrocephalus (obstructive or communicating); any ↑ ICP where CSF drainage is needed; combined ICP monitoring + treatment |
| Technique | Burr hole at Kocher's point (2.5 cm lateral to midline, 1 cm anterior to coronal suture) → catheter inserted into frontal horn of lateral ventricle |
| Dual function | Monitor ICP + Drain CSF to reduce ICP [1] |
| Risks | Infection (ventriculitis) — use antimicrobial-impregnated catheters [18]; iatrogenic haemorrhage; catheter malposition |
| Temporary vs Permanent | EVD is temporary. If long-term CSF diversion needed: ventriculoperitoneal shunt (VPS) or ventriculoatrial shunt (VAS) [2] |
Surgical removal of SOL [1]
| Condition | Surgical approach |
|---|---|
| Acute EDH | Craniotomy + haematoma evacuation [5]. Open craniotomy allows more complete evacuation. Indications: haematoma clot volume ≥ 30 cm³, thickness ≥ 1.5 cm, GCS ≤ 8 (any single criterion) |
| Conservative management for EDH (if ALL met) | Clot volume < 30 cm³ AND thickness < 1.5 cm AND GCS > 8 [5] |
| Acute SDH | Craniotomy + evacuation. Indications: SDH > 10 mm thickness or midline shift > 5 mm |
| Chronic SDH | Burr hole drainage (simpler procedure) ± subdural drain. May need craniotomy if loculated/recurrent |
| ICH | Limited evidence for routine surgical evacuation for most patients [5]. Indications: cerebellar haemorrhage with neurological deterioration / brainstem compression / hydrocephalus; supratentorial ICH in select patients (GCS 9–12, large haematoma with midline shift, or ICP refractory to medical Rx) [5] |
| Brain tumour | Resection with maximal removal within safety limit [15]. Stereotactic biopsy if non-resectable. CSF shunting for associated hydrocephalus |
| Brain abscess | Aspiration (stereotactic or open) + prolonged IV antibiotics |
| SAH | Aneurysm repair (surgical clipping OR endovascular coiling) within 24–72 h when possible to prevent rebleeding [5] |
Decompressive craniectomy [1]
| Property | Detail |
|---|---|
| Principle | Removal of a large piece of skull bone (bone flap) → removes the rigid constraint of the Monro-Kellie doctrine → allows brain to swell outward without ↑ ICP [5] |
| Indications | Massive infarction (malignant MCA syndrome) or post-TBI brain swelling [1]. Refractory ↑ ICP despite maximal medical therapy |
| Effectiveness | Effective in lowering ICP & mortality [1] |
| Limitations | Primary pathology (deficit) unchanged. Quality of survival variable. Ethical & philosophical issues [1]. ↓ Mortality but poor quality of survival; not recommended in guidelines but still done a lot [7] |
| Evidence | RCTs (DECIMAL, DESTINY, HAMLET for stroke; RESCUEicp for TBI) show ↓ mortality but ↑ proportion surviving with severe disability |
| Complications | Herniation through skull defect, CSF leakage, wound infection, epidural/subdural haematoma [5]. Risk of focal deficit due to atmospheric pressure on exposed brain (syndrome of the trephined) |
| Follow-up | Bone flap not replaced initially [1]. Can be followed by cranioplasty in 2–3 months — use autologous skull graft if early, prosthesis (e.g. titanium mesh) if late [2] |
- Alternative to shunting in obstructive hydrocephalus (especially aqueductal stenosis)
- Endoscope used to create a hole in the floor of the third ventricle → CSF bypasses the obstruction and flows directly into the basal cisterns
- Advantage: avoids shunt-related complications (infection, mechanical failure)
- Mainly used in non-communicating hydrocephalus and NPH (selected cases)
- Ventriculoperitoneal shunt (VPS): catheter from lateral ventricle → subcutaneous tunnel → peritoneal cavity. Most common permanent CSF diversion
- Ventriculoatrial shunt (VAS): catheter from lateral ventricle → right atrium (if peritoneum not suitable, e.g. after peritonitis)
- Indications: Chronic communicating hydrocephalus, NPH (responds well to CSF diversion) [1], post-SAH hydrocephalus, failed ETV
- Complications: Shunt infection (Staph. epidermidis most common), shunt malfunction (obstruction, over-drainage), subdural haematoma from over-drainage, shunt nephritis (VAS)
| Condition | Specific management notes |
|---|---|
| Brain tumour | High-dose glucocorticoids (dexamethasone) for vasogenic oedema [15]. Anti-epileptic for supratentorial lesions. Definitive: surgery ± radiotherapy ± chemotherapy. CSF shunting for hydrocephalus in posterior fossa lesions [15] |
| TBI | Tranexamic acid: loading 1 g then 500 mg Q8H IV [7] (CRASH-3 trial: benefit in mild-moderate TBI with reactive pupils). Reverse anticoagulation: PLT transfusion (for antiplatelets), vit K / FFP / 4-factor PCC (for warfarin), idarucizumab (for dabigatran) [7]. Seizure prophylaxis for 1 week [7]. Stress ulcer prophylaxis by H2 blockers [7]. DVT prophylaxis: graded compression stockings [18]. Nutrition: feeding by at least Day 5 [18] |
| ICH | BP management: IV labetalol if SBP > 150 (unless evidence of increased ICP). Target SBP < 140, avoid rapid reduction [4]. Reverse anticoagulation. Acute hydrocephalus: burr hole + EVD [4] |
| SAH | Nimodipine 60 mg Q4H PO for 21 days (for vasospasm prevention). Early aneurysm repair (coiling or clipping). EVD for acute hydrocephalus. Euvolaemia/normovolaemia |
| Malignant MCA syndrome | Medical: elevate bed head, IV mannitol, hyperventilation (salvage). Surgical: external ventricular drainage, emergency hemicraniectomy [20] |
| Bacterial meningitis | Empirical antibiotics ≤ 1 hour + dexamethasone (before or with first antibiotic dose). Treat ↑ICP medically. EVD if hydrocephalus |
| IIH | Dietary changes to ↓weight (obesity is a RF) [2][8]. CA inhibitor (1st line): acetazolamide (Diamox), topiramate [2][8]. ± Diuretics: furosemide (if refractory) [8]. Short-course corticosteroids: prednisolone [2]. Serial LPs to ↓ICP [2]. Optic nerve fenestration (ONSF) and/or CSF shunting if progressive visual loss [2][8] |
| Acute liver failure | Mannitol, hyperventilation, barbiturate coma (if refractory) [19]. Dexamethasone is NOT useful in ↑ICP due to acute liver failure [19]. CRRT preferred over IHD (more haemodynamically stable, better for cerebral oedema) [21] |
| NPH | CSF diversion: VP shunting or ETV. Need to distinguish from other causes of dementia such as AD, which does not respond to shunting [1] |
| Do NOT | Why not |
|---|---|
| Give mannitol if shocked [7] | Mannitol causes massive osmotic diuresis → ↓ intravascular volume → worsens shock → ↓ CPP |
| Blindly hyperventilate [7] | Over-ventilation (PaCO₂ < 30 mmHg) → excessive vasoconstriction → ↓ CBF → cerebral ischaemia |
| Use barbiturate/propofol outside ICU [7] | Risk of cardiovascular collapse (hypotension, myocardial depression) without invasive monitoring |
| Give steroids in TBI [7] | CRASH trial (> 10,000 patients): high-dose methylprednisolone in TBI → ↑ 14-day mortality |
| Put in a jugular central line in ↑ICP patient [2] | Risk of jugular vein thrombosis → impedes venous drainage → worsens ICP. Use subclavian or femoral instead |
| Perform LP without prior imaging when mass lesion suspected | Risk of tonsillar herniation (coning) |
High Yield Summary
-
ABC before ICP! Always resuscitate first. CPP = MAP − ICP; if MAP is low, brain ischaemia occurs even with normal ICP.
-
General measures (Tier 0): Head up 30°, neck neutral, sedation, analgesia, euvolaemia, seizure prevention, temperature control, glucose/electrolyte optimisation.
-
Tier 1 (any doctor): Osmotherapy (mannitol 0.25–1 g/kg, onset 15 min, or hypertonic saline if shocked) + controlled hyperventilation (PaCO₂ 30–35 mmHg, short-term only).
-
Tier 2 (ICU): Barbiturate coma (last resort, requires EEG monitoring) ± decompressive craniectomy.
-
Steroids: Only for tumour-associated vasogenic oedema and CNS infections. NEVER for TBI or stroke.
-
EVD = gold standard for ICP monitoring AND therapeutic CSF drainage.
-
Decompressive craniectomy: Effective in ↓ ICP and mortality but quality of survival is variable.
-
Treat the cause: EDH → craniotomy; SDH → craniotomy or burr hole; ICH → select cases; tumour → resection; hydrocephalus → EVD/ETV/VP shunt; IIH → weight loss + acetazolamide; SAH → aneurysm repair.
-
Treatment targets: ICP < 22 mmHg, CPP 60–70 mmHg, normocapnia, normoglycaemia, normonatraemia, normothermia.
-
Do NOT: Give mannitol if shocked, blindly hyperventilate, use barbiturates outside ICU, give steroids in TBI, insert jugular lines in ↑ICP patients.
Active Recall - Management of Raised ICP
References
[1] Lecture slides: GC 111. Raised intracranial pressure and hydrocephalus.pdf (pp. 9–10, 14) [2] Senior notes: Ryan Ho Neurology.pdf (pp. 156–157) [4] Senior notes: maxim.md (ICH management section) [5] Senior notes: felixlai.md (ICP management and treatment sections) [7] Senior notes: Ryan Ho Fundamentals.pdf (p. 339) [8] Senior notes: Ryan Ho Opthalmology.pdf (p. 90) [15] Senior notes: Ryan Ho Neurology.pdf (p. 163) [17] Senior notes: Ryan Ho Urogenital.pdf (p. 17) [18] Senior notes: maxim.md (Severe TBI management section) [19] Senior notes: Ryan Ho GI.pdf (p. 207) [20] Senior notes: Ryan Ho Neurology.pdf (p. 81) [21] Senior notes: Ryan Ho Urogenital.pdf (p. 98)
Complications of Raised Intracranial Pressure
Raised ICP generates complications through two fundamental mechanisms we established at the start of these notes:
- Global: ↓ CPP → ↓ CBF → cerebral ischaemia
- Focal: Pressure gradients across dural compartments → brain herniation → brainstem compression
Additionally, both the underlying cause of raised ICP and the treatments themselves carry their own complications. A comprehensive approach therefore considers complications in three domains: (A) Direct consequences of raised ICP itself, (B) Complications of the underlying disease, and (C) Complications of treatment (iatrogenic).
A. Direct Complications of Raised ICP
This is the most feared and immediately life-threatening complication. Detailed herniation syndromes were covered in the clinical features section but are revisited here because they represent the catastrophic endpoint of uncontrolled raised ICP.
| Herniation type | Structures herniated / compressed | Clinical consequence | Why it happens |
|---|---|---|---|
| Uncal (transtentorial) | Uncus of temporal lobe through tentorial notch → compresses ipsilateral CN III, ipsilateral cerebral peduncle, PCA, brainstem | Ipsilateral fixed dilated pupil → contralateral hemiparesis → progressive ↓ GCS → coma → death | Unilateral supratentorial mass creates pressure gradient across tentorium cerebelli. The uncus, being the most medial part of the temporal lobe, is pushed downward first |
| Central (transtentorial) | Bilateral diencephalon downward through tentorial notch | Bilateral small pupils → Cheyne-Stokes respiration → loss of consciousness → bilateral motor signs [2] | Midline or diffuse bilateral supratentorial pathology compresses both sides symmetrically |
| Tonsillar (coning) | Cerebellar tonsils through foramen magnum → compresses medulla | Cardiorespiratory arrest, loss of consciousness, bilateral dilated pupils, decorticate or decerebrate posture [2] | Posterior fossa mass or downward pressure from above. The medulla houses vital cardiorespiratory centres — their compression is immediately lethal |
| Subfalcine (cingulate) | Cingulate gyrus under falx cerebri → compresses ACA | Bilateral lower limb weakness (ACA territory ischaemia). Contralateral hydrocephalus (foramen of Monro compressed) [2] | Early unilateral supratentorial mass. Often a precursor to uncal herniation |
| Transcalvarial (external) | Brain herniates through skull defect (fracture or craniectomy site) | Visible "mushrooming" of brain tissue [5] | Skull is no longer intact — the path of least resistance is outward |
Herniation = Point of No Return
Once brainstem herniation is established and bilateral fixed dilated pupils are present with loss of brainstem reflexes, the prognosis is almost universally fatal. This is why aggressive ICP management and early neurosurgical consultation are critical — the goal is to prevent herniation, not treat it after it has occurred.
- Mechanism: ↑ ICP → ↓ CPP (CPP = MAP − ICP) → ↓ CBF → watershed ischaemia first (boundary zones between major arterial territories are most vulnerable), then global ischaemia if CPP approaches zero
- Post-traumatic brain ischaemia: In TBI, cerebral autoregulation is impaired (pressure-passive system [6]) → any drop in MAP directly translates to ↓ CBF → secondary ischaemic injury on top of the primary traumatic injury
- This creates a vicious cycle: ischaemia → more oedema → more ↑ ICP → more ischaemia → neuronal death
- Clinical significance: Secondary ischaemic injury is the leading cause of morbidity and mortality in TBI — it is potentially preventable, which is why maintaining CPP 60–70 mmHg is paramount
- Chronic papilloedema can cause permanent optic nerve damage [8]
- Mechanism: Sustained ↑ ICP → chronic "tourniquet" effect on the optic nerve → progressive axonal loss → optic atrophy → irreversible constriction of visual fields → blindness
- Particularly relevant in IIH: 25% at risk of severe permanent vision loss [2]
- Transient visual obscurations (TVOs) are a warning sign — increasing intensity, frequency and duration of TVOs can be a prognostic sign for permanent visual loss [8]
- The Cushing reflex (hypertension + bradycardia + irregular respiration) is not just a clinical sign — the severe hypertension itself can cause:
- Cardiac arrhythmias
- Myocardial injury (neurogenic stunned myocardium)
- Neurogenic pulmonary oedema — a sudden surge in sympathetic activity increases pulmonary capillary pressure → pulmonary oedema without underlying cardiac failure [22]
- Seizure can both complicate and cause increased ICP [5]
- Why seizures complicate raised ICP: Cortical irritation from mass effect, oedema, or focal ischaemia lowers the seizure threshold → abnormal neuronal firing
- Why seizures worsen ICP: Seizures cause hyperaemia and exacerbate ↑ICP [7] — a seizure massively increases cerebral metabolic demand → reflex vasodilation → ↑ CBV → ↑ ICP. This creates a dangerous positive feedback loop
- Post-traumatic seizures: Early (< 7 days) and late (> 7 days). Prophylactic AEDs reduce early but not late seizures [7]
6. Endocrine and Electrolyte Complications
- CNS causes of SIADH include: infections (meningitis, encephalitis, brain abscess), head trauma, SAH, CVA, ↑ICP [17]
- Mechanism: The hypothalamic-neurohypophyseal axis is disrupted → non-physiological ↑ ADH secretion → water retention → euvolaemic hyponatraemia
- Hyponatraemia itself causes further cerebral oedema (osmotic gradient drives water into neurons) → worsens ↑ ICP → vicious cycle
- Goal of treatment: prevent brain herniation due to cerebral oedema [17]
- Important differential of SIADH in neurosurgical patients [17]
- Mechanism: Inappropriate natriuresis + diuresis secondary to cerebral disorder (possibly via BNP release from damaged brain)
- Results in hypovolaemic hyponatraemia (unlike SIADH which is euvolaemic)
- Treatment is opposite to SIADH: CSWS needs volume replacement with saline, whereas SIADH needs fluid restriction
- Both can follow head pathologies. CSWS results in renal Na loss → hypovolaemic hyponatraemia; SIADH results in renal water retention → euvolaemic hyponatraemia (different treatment) [17]
SIADH vs CSWS — Get This Right!
Both occur after CNS pathology and both cause hyponatraemia. But the volume status is different: SIADH = euvolaemic (fluid restrict); CSWS = hypovolaemic (give saline). Giving saline to SIADH or restricting fluids in CSWS will worsen the patient. Always assess volume status clinically.
- Can occur after hypothalamic/pituitary damage (e.g. post-traumatic, post-neurosurgery, pituitary apoplexy)
- Mechanism: ↓ ADH secretion → inability to concentrate urine → massive polyuria → hypernatraemia + dehydration
- Hypernatraemia itself can worsen brain injury (neuronal shrinkage)
B. Complications of the Underlying Disease
| Complication | Pathophysiology | Details |
|---|---|---|
| Post-traumatic brain swelling | Multifactorial: vasogenic oedema (disrupted BBB), cytotoxic oedema (neuronal injury), reactive hyperaemia (impaired autoregulation) [6] | Creates vicious cycle with ↑ ICP. Very difficult to treat because of multifactorial origin |
| Diffuse axonal injury (DAI) | Rotational injury → shearing of axons → diffuse WM tract lesions | Profound coma but often without elevated ICP initially. Often clinico-radiological dissociation [6] — clinical severity disproportionate to CT findings. Poor functional recovery |
| Post-traumatic epilepsy | Scar tissue formation → abnormal neuronal circuits → chronic seizure focus | Early seizures (< 7 d) prevented by prophylactic AEDs; late seizures (> 7 d) are NOT prevented by prophylaxis [7] |
| Post-concussion syndrome | Milder axonal damage (impaired axonal transport → axonal swelling, Wallerian degeneration) | Headache, dizziness, fatigue, irritability, concentration difficulty, memory problems. Usually resolves in weeks–months but can persist |
| CSF fistula | Skull base fracture → dural tear → CSF leakage | CSF rhinorrhoea (anterior fossa), CSF otorrhoea (middle fossa). Risk of ascending meningitis. Usually heals spontaneously; may need surgical repair if persistent |
SAH deserves special mention because it produces a characteristic constellation of complications that can each worsen ICP [22]:
| Complication | Timing | Mechanism |
|---|---|---|
| Re-bleeding | 3–4% in first 24 h, 1–2% each day in the first month [5] | Unsecured aneurysm re-ruptures. Mortality 70% with re-rupture → this is why early aneurysm repair is critical |
| Delayed cerebral ischaemia (DCI) / Vasospasm | Peak days 4–14 | Breakdown products of blood in subarachnoid space cause arterial spasm → ↓ CBF → ischaemic stroke. Prevented by nimodipine. Treated by haemodynamic augmentation, IA vasodilators, angioplasty [22] |
| Acute hydrocephalus | Hours to days | Blood products obstruct arachnoid granulations or clog the ventricular system → communicating or obstructive hydrocephalus |
| Hyponatraemia | Days | SIADH or CSWS (see above) |
| Neurogenic pulmonary oedema | Hours | Massive sympathetic surge → ↑ pulmonary capillary pressure |
| Cardiac complications | Hours to days | Neurogenic stunned myocardium, arrhythmias, Takotsubo cardiomyopathy |
CNS complications [23]:
- Seizures, cerebral oedema, hydrocephalus, herniation
Systemic complications [23]:
- Myocardial infarction, heart failure, dysphagia, aspiration pneumonia, UTI, DVT, PE, dehydration, malnutrition, pressure sores, orthopaedic complications and contractures, post-stroke depression
Complications mainly occur in pyogenic and chronic meningitis [15]:
- Basal meningeal adhesions due to incomplete organisation of inflammatory exudates → Hydrocephalus → ↑ICP and CN palsies (III, IV, VI commonest; VIII involvement tends to persist)
- Arteritis/thrombophlebitis leading to cerebral infarction
- Parenchymal damage → neurological sequelae: intellectual impairment, mental retardation or cerebral palsy
- Seizures: occur in 10% of acute bacterial meningitis, ~5% develop epilepsy
- Spread of infection: locally → cerebritis, cerebral abscess, subdural effusion/empyema; systemically → arthritis, IE
- SIADH → hyponatraemia [15]
C. Complications of Treatment (Iatrogenic)
| Complication | Mechanism |
|---|---|
| Hypovolaemia and hypotension | Osmotic diuresis → ↓ intravascular volume → ↓ MAP → ↓ CPP (the opposite of what you want) |
| Hyperosmolality | Serum osmolarity > 320 → renal failure risk, confusion, seizures |
| Rebound cerebral oedema | If stopped abruptly, mannitol that has leaked across a damaged BBB into brain tissue draws water in → paradoxical worsening. Must taper [2] |
| Acute tubular necrosis | High-dose mannitol in patients with pre-existing renal impairment |
| Hypernatraemia, dehydration | Loss of free water through osmotic diuresis |
| Volume overload (transient) | Mannitol is an immediate plasma expander before the diuresis kicks in → can precipitate heart failure [2] |
| Complication | Mechanism |
|---|---|
| Cerebral ischaemia | Excessive vasoconstriction → ↑ CVR → ↓ CBF (undesirable) [5] |
| Rebound ↑ ICP | Abrupt normalisation of PaCO₂ → sudden vasodilation → ↑ CBV → ICP spike. Must taper gradually |
| Respiratory alkalosis | Electrolyte shifts (↓ ionised Ca²⁺ → tetany, arrhythmia) |
These are extremely high-yield for exams and were emphasised on the lecture slides:
Complications of CSF Shunt: [1]
| Complication | Mechanism / Details |
|---|---|
| Infection (1° or 2°) [1] | Pathogens: S. epidermidis, S. aureus [3]. S/S: fever, lethargy, meningism, S/S of raised ICP. Infected shunts must be removed (bridge by EVD for 4–6 weeks) [2] |
| Blockage → hydrocephalus [1] | Site: 80% proximal block, 10% valve, 10% distal block [3]. Causes: choroid plexus, brain parenchyma, protein, tumour cells ingrowth. Ix: urgent CT brain + shunt series (plain XR of entire shunt) [3]. Mx: shunt revision or ETV |
| Dislodgement / Fracture → hydrocephalus [1] | Catheter disconnection or fracture along its subcutaneous course |
| Over-shunting → chronic SDH (CSDH) [1] | Excessive CSF drainage → brain "sags" away from skull → stretching and tearing of bridging veins → chronic subdural haematoma. Also causes postural headache (worse standing, relieved lying down — intracranial hypotension) [2] |
| Abdominal pseudocyst [1] | Distal VP catheter tip becomes walled off by peritoneum → CSF-filled cyst forms → presents as abdominal distension ± pain |
| Slit ventricle syndrome [1] | Nightmare scenario: long-term shunting changes compliance of brain and ventricles → ventricles do not dilate despite ↑↑↑ ICP [2]. Must compare carefully with previous CT for subtle enlargement. Very difficult to manage |
| Nephritis (VA shunt) [1] | Immune complex deposition in kidneys from chronic low-grade bacteraemia (shunt nephritis). Specific to VA shunts because the distal tip is in the bloodstream |
| Bowel perforation (VP shunt) [1] | Distal catheter erodes through bowel wall → peritonitis, faecal contamination of shunt |
| Tumour seeding [3] | Rare — malignant cells travel along shunt catheter from ventricle to peritoneum/atrium |
Common Scenarios (from lecture slides) [1]:
- Recurrent hydrocephalic symptoms → Blocked shunt? Test shunt if you know what you are doing
- Raised ICP symptoms ± focal deficit → CSDH? (e.g. elderly on aspirin)
- Postural headache (worse when erect) → Intracranial hypotension? (e.g. over-shunting without CSDH)
- Fever + abdominal pain → Shunt infection causing peritonitis? Peritonitis causing shunt infection? → Externalise shunt + antibiotics
Shunt Complication Pearls
- Do NOT pump the shunt to test it — valve pumping is not accurate, not sensitive, not specific. Do NOT pump (will over-shunt CSF) [2]. You can press once to differentiate distal from proximal obstruction (two one-way valves).
- Shuntogram (inject contrast into shunt) is the workup for suspected blockage [2].
- S/S of shunt malfunction are stereotypical — ask the patient what their symptoms were during previous shunt failures; they often know [2].
| Complication | Mechanism |
|---|---|
| Herniation through skull defect [5] | Brain bulges through the bony defect — can be acutely worsened by positional changes |
| CSF leakage [5] | Lack of bony covering → disrupted wound healing |
| Wound infection [5] | Large surgical wound with exposed dura |
| Epidural and subdural haematoma [5] | Surgical trauma ± coagulopathy |
| Syndrome of the trephined | Risk of focal deficit due to atmospheric pressure on exposed brain [2]. Patients may paradoxically deteriorate after craniectomy → improves after cranioplasty (replacement of bone flap) |
| Hydrocephalus | Altered CSF dynamics post-craniectomy |
| Quality of survival variable, ethical and philosophical issues [1] | RESCUEicp trial: ↓ mortality but ↑ proportion surviving with severe disability. Primary pathology (deficit) unchanged [1] |
- Risk of ↓BP, infection, electrolyte problems [7]
- Myocardial depression → cardiovascular collapse if not in ICU with invasive monitoring
- Immunosuppression → ↑ risk of nosocomial infections (pneumonia, UTI)
- Paralytic ileus — prolonged sedation affects gut motility
- Renders neurological examination impossible for the duration of therapy
- S/E includes PUD (need prophylaxis), immunosuppression, Cushingoid features [2]
- Hyperglycaemia — can worsen ischaemic brain injury
- Delayed wound healing — important post-operatively
- Steroid myopathy — prolonged use causes proximal muscle weakness
- Psychiatric effects — insomnia, agitation, psychosis
Patients with severe raised ICP (particularly TBI and SAH) are often in ICU for prolonged periods. The systemic complications of immobility and critical illness overlap with those of stroke:
| System | Complications | Prevention |
|---|---|---|
| Respiratory | Aspiration pneumonia (↓ GCS → loss of airway protective reflexes), ventilator-associated pneumonia, neurogenic pulmonary oedema, ARDS | Early intubation if GCS ≤ 8, careful feeding practice, chest physiotherapy, early tracheostomy for prolonged ventilation |
| Cardiovascular | DVT, PE, neurogenic cardiac injury, arrhythmias | DVT prophylaxis: graded compression stockings [18]. Consider LMWH after 1–4 days if bleeding has ceased [5] |
| GI | Stress ulcers (Cushing's ulcers — named after Harvey Cushing; raised ICP → vagal stimulation → ↑ gastric acid), paralytic ileus | Stress ulcer prophylaxis by H2 blockers [7] or PPI. Nutrition: feeding by Day 5 [18] |
| Renal/Metabolic | AKI (from mannitol, hypotension), electrolyte disturbances (hypoNa from SIADH/CSWS, hyperNa from DI or mannitol) | Monitor U&E, osmolality, urine output. Correct electrolytes carefully |
| Musculoskeletal | Pressure sores, contractures, frozen shoulder, heterotopic ossification | Frequent repositioning, early physiotherapy, specialised mattress |
| Infectious | UTI (from indwelling catheters), wound infections, meningitis/ventriculitis (from EVD/shunt) | Minimise catheter duration, aseptic technique, antimicrobial-impregnated EVD catheters |
| Psychiatric | Post-stroke depression (prevalence ~29% at any time after stroke [23]). Post-TBI depression, anxiety, PTSD, personality changes | Early screening, psychiatric referral, pharmacotherapy when indicated |
| Nutritional | Malnutrition, catabolism | Early enteral nutrition, adequate protein and calorie supplementation |
High Yield Summary
-
Most feared complication: Brain herniation (uncal → blown pupil + contralateral hemiparesis; tonsillar → cardiorespiratory arrest). This is what kills patients with uncontrolled raised ICP.
-
Global ischaemia: ↑ ICP → ↓ CPP → ↓ CBF → secondary ischaemic injury. Vicious cycle because ischaemia → more oedema → more ↑ ICP.
-
Visual loss: Chronic papilloedema → optic atrophy → permanent blindness. 25% of IIH patients at risk.
-
SIADH vs CSWS: Both cause hyponatraemia after CNS pathology. SIADH = euvolaemic (fluid restrict); CSWS = hypovolaemic (give saline). Getting this wrong is dangerous.
-
SAH complications (9H mnemonic): Haematoma, intracranial HT, systemic HT, HF/arrhythmia, Haemorrhage (rebleed), Hypoperfusion (DCI/vasospasm), Hydrocephalus, Hypovolaemia (CSW), HypoNa (SIADH).
-
Shunt complications: Infection (S. epidermidis; remove shunt + EVD bridge), Blockage (80% proximal), Over-shunting → CSDH, Abdominal pseudocyst, Slit ventricle syndrome, Nephritis (VA), Bowel perforation (VP), Tumour seeding.
-
Decompressive craniectomy: ↓ ICP and mortality but quality of survival is variable. Complications include herniation through defect, syndrome of the trephined, infection, CSF leak.
-
Mannitol complications: Hypovolaemia/hypotension (do NOT give if shocked), hyperosmolality, rebound oedema (taper, do not stop abruptly), renal failure.
-
Systemic complications: Aspiration pneumonia, DVT/PE, stress ulcers (Cushing's ulcers), SIADH/CSWS, pressure sores, post-TBI depression.
Active Recall - Complications of Raised ICP
References
[1] Lecture slides: GC 111. Raised intracranial pressure and hydrocephalus.pdf (pp. 9, 17) [2] Senior notes: Ryan Ho Neurology.pdf (pp. 153, 156–157, 160) [3] Senior notes: maxim.md (Complications of CSF shunt section) [5] Senior notes: felixlai.md (ICP treatment, decompressive craniectomy complications, hydrocephalus sections) [6] Senior notes: Ryan Ho Neurology.pdf (p. 205, Secondary brain injury) [7] Senior notes: Ryan Ho Fundamentals.pdf (p. 339) [8] Senior notes: Ryan Ho Opthalmology.pdf (p. 90) [15] Senior notes: Ryan Ho Neurology.pdf (pp. 145, 163) [17] Senior notes: Ryan Ho Urogenital.pdf (p. 17) [18] Senior notes: maxim.md (Severe TBI management section) [19] Senior notes: Ryan Ho GI.pdf (p. 207) [22] Senior notes: maxim.md (SAH complications section) [23] Senior notes: felixlai.md (Stroke complications and prognosis section)
High Yield Summary — Etiology & pathophysiology
Definition: Sustained intracranial pressure above physiological range; often treatment threshold ~20–22 mmHg in adults (context-dependent).
Normal: Adult ~10–15 mmHg; infant lower; CPP = MAP − ICP (or MAP − JVP when extracranial venous pressure is the effective downstream pressure).
Monro–Kellie–Burrows: Fixed skull volume → brain + blood + CSF; compensation via CSF displacement then venous egress; then steep ICP rise (compliance curve).
Drivers of ↑ICP: Mass (tumour, haematoma), cerebral oedema (vasogenic BBB leak vs cytotoxic cellular swelling vs interstitial transependymal CSF), impaired venous outflow, hydrocephalus, status epilepticus, hypercapnia, fever.
Cushing reflex (late): ↑BP, bradycardia, irregular respiration — brainstem compression; not reliable early warning.
IIH (pseudotumour cerebri): Obese young women; elevated ICP with normal imaging (except empty sella / slit ventricles); CN VI palsy common; visual field loss from papilloedema — preserve sight.
High Yield Summary — Differential diagnosis
Think by mechanism: Space-occupying lesion, diffuse oedema (TBI, stroke, metabolic), CSF pathway failure (hydrocephalus), venous obstruction (sinus thrombosis), malignant hypertension, hypercapnia, drugs/toxins, IIH.
Mimics of ↑ICP headache: Migraine, CSF hypotension, cervical pathology, medication overuse — but true localising neuro signs + papilloedema demand urgent imaging.
Herniation patterns: Uncal (unilateral pupil, contralateral hemiparesis may be "false localising"); central; tonsillar (respiratory arrest risk).
High Yield Summary — Diagnosis & monitoring
Clinical: GCS trend, pupil size/reactivity, posturing, CN VI, fundoscopy (papilloedema often late in acute trauma).
Imaging: Non-contrast CT emergency — mass, midline shift, basal cistern effacement, hydrocephalus, blood. MRI when stable for aetiology.
Invasive ICP monitoring: EVD therapeutic + monitoring; parenchymal bolt — indications per TBI protocol and neurosurgical context (often GCS ≤8 with abnormal CT in severe TBI cohorts — follow current guideline nuance).
Don't forget: ABCDE before chasing numbers; hypotension and hypoxia worsen outcome more than a single ICP reading.
High Yield Summary — Management
Tier 0 — General (any doctor): Airway (intubate if GCS ≤8 / failing protection), oxygen, normocapnia (avoid routine prolonged hyperventilation), maintain MAP for CPP ~60–70, head-up ~30°, midline neck, treat seizures, pyrexia, euvolaemia, analgesia/sedation.
Tier 1 — Osmotherapy: Mannitol 0.25–1 g/kg (avoid if hypovolaemic / shocked; foley — diuresis) or hypertonic saline (central line for high concentrations).
Tier 2 — Brief hyperventilation: PaCO₂ 30–35 mmHg only short bridge — vasoconstriction → ↓CBF → ischaemia risk if prolonged.
Tier 3 — Advanced ICU / neurosurgery: Barbiturate coma, decompressive craniectomy, therapeutic hypothermia (select adult contexts — know exam frame used locally).
Surgical cause control: Evacuate haematoma, resect tumour, EVD for hydrocephalus.
Avoid: Steroids not for TBI (harm — CRASH); jugular lines / tight collars impairing venous drainage.
High Yield Summary — Complications
Brain: Ischaemia from low CPP, herniation, stroke from herniation-related vessel compression, Duret haemorrhages.
Systemic: ARDS from aggressive fluids, renal injury from mannitol, hypernatraemia, rebound ICP if osmotherapy withdrawn abruptly.
IIH-specific: Permanent visual loss — serial fields, fundoscopy, consider emergent optic nerve sheath fenestration if shunt/ medical Rx failing.
Monitoring risks: Haemorrhage at catheter site, infection.
Hydrocephalus
Hydrocephalus is a condition characterized by abnormal accumulation of cerebrospinal fluid within the ventricular system of the brain, leading to increased intracranial pressure and ventricular dilation.
Intracranial Hemorrhage
Intracranial hemorrhage is bleeding within the cranial vault—including epidural, subdural, subarachnoid, or intraparenchymal compartments—resulting from trauma, vascular malformations, or coagulopathy and potentially causing elevated intracranial pressure and neurological compromise.