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.
Hydrocephalus — from Greek "hydro" = water + "cephalus" = head — literally "water on the brain." It is a condition characterised by the accumulation of excess cerebrospinal fluid (CSF) within the cranium, leading to dilatation of the cerebral ventricles (ventriculomegaly) and/or subarachnoid spaces [1][2][3].
The key concept here is a mismatch between CSF production, circulation, and absorption. When any part of this delicate balance is disrupted, CSF accumulates, pressure rises (or in chronic cases, the ventricles expand even without markedly raised pressure), and the brain parenchyma is compressed.
Core Concept
Hydrocephalus is NOT a single disease — it is a syndrome caused by multiple possible aetiologies. Think of it as the final common pathway of any process that disrupts CSF dynamics.
- Congenital hydrocephalus: incidence ~0.5–1 per 1,000 live births globally [4]
- In Hong Kong, the incidence has decreased due to improved antenatal screening (ultrasound detection of ventriculomegaly) and periconceptional folate supplementation (reducing neural tube defects which are associated with hydrocephalus) [5]
- Acquired hydrocephalus: can occur at any age
- Common causes in adults in Hong Kong: post-subarachnoid haemorrhage (SAH), post-meningitis (especially TB meningitis — still relevant in Hong Kong), brain tumours, intracerebral haemorrhage (ICH)
- Normal Pressure Hydrocephalus (NPH): typically affects adults > 65 years old; prevalence ~1–3% of those with dementia [1][3]
- A surgically treatable cause of cognitive decline — this is why it matters so much [1]
Risk Factors
- Congenital: prematurity (intraventricular haemorrhage/IVH), neural tube defects, congenital infections (TORCH), genetic syndromes
- Acquired: prior SAH, meningitis (bacterial, TB, cryptococcal — all relevant in HK), intracranial tumours, head trauma, intracranial haemorrhage
- NPH: prior SAH, prior meningitis, idiopathic (majority)
Anatomy and CSF Physiology
Understanding hydrocephalus from first principles requires a solid grasp of CSF dynamics. Let's build this up step by step.
- Average total CSF volume: ~150 mL [3]
- 20% within the ventricular system
- 80% in the subarachnoid and cisternal spaces
- Production rate: ~450–500 mL/day (i.e. the entire CSF volume is renewed approximately 3 times per day) [1][3]
- This means CSF is not a stagnant pool — it is in constant flow. Any obstruction, even partial, can cause rapid accumulation.
- Active secretion primarily by the choroid plexus (~75%) located within the lateral ventricles (most), 3rd ventricle, and 4th ventricle [2][3]
- Remaining ~25% from other sources: ependymal wall, brain parenchyma interstitial fluid [3]
- Mechanism: choroid plexus epithelial cells actively transport Na⁺ and HCO₃⁻ into the ventricles, with water following osmotically. Carbonic anhydrase is critical in this process — this is why acetazolamide (a carbonic anhydrase inhibitor) can reduce CSF production.
The pathway follows a predictable anatomical route — and each bottleneck is a potential site of obstruction:
Why the Aqueduct of Sylvius Matters
The cerebral aqueduct (aqueduct of Sylvius) is the narrowest point in the entire CSF pathway (~1–2 mm diameter). This makes it the most vulnerable to obstruction — whether by congenital stenosis, tumour compression, or post-inflammatory gliosis. Aqueductal stenosis is one of the most common causes of obstructive hydrocephalus.
- Primary route (~80%): Arachnoid granulations (also called arachnoid villi) — these are finger-like projections of arachnoid membrane that protrude into the dural venous sinuses, predominantly the superior sagittal sinus [2][3]
- Absorption is passive and pressure-dependent: CSF flows into the venous sinus when CSF pressure exceeds venous sinus pressure (i.e. down a pressure gradient)
- This is why venous sinus thrombosis can cause communicating hydrocephalus — the pressure gradient is reversed
- Secondary route (~20%): Extracranial lymphatics — via the subarachnoid space around exiting cranial nerves (especially the olfactory nerve/cribriform plate) and perivascular (Virchow-Robin) spaces [3]
The skull is a rigid structure with constant volume (after fontanelle and suture closure) [5]:
- Brain parenchyma: ~80%
- Blood (arterial + venous): ~10%
- CSF: ~10%
An increase in any one compartment must be compensated by a decrease in others, primarily through [5]:
- CSF outflow from cranium to spinal subarachnoid space (slow compensatory mechanism)
- Venous blood outflow from cranial sinuses (rapid compensatory mechanism)
When these compensatory mechanisms are overwhelmed, intracranial pressure (ICP) rises steeply — this is the exponential portion of the pressure-volume (elastance) curve.
Exception: In infants, the sutures and fontanelles are not yet fused → the cranial cavity is expansile → ICP may not rise significantly, but the head progressively enlarges [1][2][5]. This is why infants present with macrocephaly rather than the classic raised ICP signs seen in adults.
Pathogenetic Mechanisms
There are three fundamental mechanisms by which hydrocephalus develops [1][2]:
| Mechanism | Pathophysiology | Examples |
|---|---|---|
| ↑ CSF production | Overproduction exceeds absorption capacity (rare) | Choroid plexus papilloma [1][2] |
| Flow obstruction | Physical blockage within ventricular system or at outlet foramina | Tumour, haematoma, aqueductal stenosis [1][2] |
| ↓ CSF absorption | Impaired absorption at arachnoid granulations | Post-meningitis (arachnoid granulation adhesions), post-SAH [1][2] |
An additional mechanism sometimes listed:
- Obstruction of venous outflow: e.g. venous sinus thrombosis, jugular vein compression — this raises venous sinus pressure, reducing the CSF-to-venous pressure gradient, thereby impairing absorption [5]
Classification
This is the most clinically important distinction, because it determines management — especially whether lumbar puncture is safe [1].
Definition: Obstruction of CSF flow within the ventricular system (i.e. before CSF exits into the subarachnoid space).
Key imaging feature: Ventricles dilated PROXIMAL to the obstruction, with normal-sized 4th ventricle (if obstruction is at or proximal to the aqueduct) [3]. If the 4th ventricle is the site of obstruction, it may be dilated too.
Why is LP dangerous? Because ventricular CSF does NOT freely communicate with the lumbar subarachnoid space. Removing CSF below the obstruction creates a transtentorial pressure gradient → risk of downward (uncal/tonsillar) herniation → brainstem compression → death [1].
"LP is absolutely contraindicated (& lethal)" in non-communicating hydrocephalus [1]
Causes of Obstructive Hydrocephalus
- Aqueductal stenosis — the most common cause of congenital hydrocephalus
- Can be primary (developmental) or secondary (post-infectious gliosis, e.g. after congenital CMV/toxoplasmosis)
- Some forms are X-linked (L1CAM mutation)
- Arnold-Chiari malformation (Type II) — downward herniation of the cerebellar vermis and brainstem through the foramen magnum, obstructing CSF flow at the posterior fossa outlet
- Strongly associated with myelomeningocele [5]
- Dandy-Walker syndrome — cystic dilatation of the 4th ventricle with agenesis/hypoplasia of the cerebellar vermis → obstruction of 4th ventricle outflow
- Neural tube defect [1]
- Congenital infection [1]
- Congenital mass lesions [1]
- Tumours — the most common acquired cause in adults:
- Posterior fossa tumours (especially in children): medulloblastoma, ependymoma, pilocytic astrocytoma — compress the 4th ventricle or aqueduct
- CPA tumours: vestibular schwannoma, meningioma
- Brain metastasis, gliomas [3]
- Craniopharyngioma / pituitary macroadenoma — can compress 3rd ventricle
- Colloid cyst of the 3rd ventricle — classically causes intermittent obstruction at the foramen of Monro, leading to episodic severe headaches and even sudden death
- Pineal region tumours — compress the aqueduct
- Vascular: cerebellar infarct (with swelling), ICH, intraventricular haemorrhage (IVH) [3]
- Infections: ventriculitis, post-infective aqueductal stenosis, brain abscess, neurocysticercosis (a trapped cyst can obstruct the 4th ventricle or aqueduct) [3]
- Chronic meningitis: TB, Cryptococcus — basal exudates can obstruct foramina [5]
Definition: Obstruction of CSF flow outside the ventricular system — i.e. ventricular CSF freely communicates with the subarachnoid space, but absorption is impaired (typically at arachnoid granulations).
Key imaging feature: ALL ventricles are dilated, including the 4th ventricle [3]
LP is diagnostic AND therapeutic in communicating hydrocephalus — because there is free communication between ventricles and the lumbar subarachnoid space [1].
"LP is diagnostic & therapeutic" in communicating hydrocephalus [1]
Causes of Communicating Hydrocephalus [1][2][3]
| Mechanism | Examples |
|---|---|
| ↑ CSF production (rare) | Choroid plexus papilloma |
| ↓ CSF absorption | Post-SAH (blood products clog arachnoid granulations), post-meningitis (especially bacterial, TB — arachnoid granulation adhesions/fibrosis), post-IVH |
| Tumours | Leptomeningeal carcinomatosis (tumour cells block arachnoid granulations) |
| Idiopathic | Normal pressure hydrocephalus (NPH) [1] |
| Venous outflow obstruction | Venous sinus thrombosis (raises venous pressure → reduces absorption gradient) |
A Critical Distinction
This classification (communicating vs non-communicating) is THE critical distinction for emergency management:
- Communicating: LP is safe and therapeutic
- Non-communicating: LP is absolutely contraindicated and potentially lethal → use external ventricular drain (EVD) instead
Always determine the type of hydrocephalus on imaging BEFORE performing LP [1].
This is classified separately because of its unique pathophysiology and clinical importance.
Normal Pressure Hydrocephalus (NPH) — In Detail
- A surgically treatable cause of cognitive decline [1]
- Chronic communicating hydrocephalus with intermittently raised ICP (ICP may be normal on single measurement, but shows pathological B-waves on continuous monitoring) [5]
- ICP not high despite large ventricles — this apparent paradox is explained by complex pathophysiology of abnormal brain compliance [1]
- Complex pathophysiology of abnormal brain compliance [1]
- The prevailing theory: early in the disease, there is a period of raised ICP (from the inciting cause, e.g. SAH, meningitis) that expands the ventricles. Over time, a new equilibrium is reached where ICP normalises, but the ventricles remain enlarged
- According to Laplace's law: Force = Pressure × Area. Even at "normal" pressure, the enlarged ventricular surface area means the total outward force on the brain parenchyma remains elevated → ongoing damage
- The expanded ventricles compress the corona radiata fibres (white matter tracts running from cortex to internal capsule) which pass alongside the lateral ventricles [5]
- This compression particularly affects:
- Periventricular motor fibres serving the lower limbs (legs are represented medially in the motor homunculus, closest to the ventricles) → gait disturbance is usually the earliest and most prominent feature
- Frontal lobe white matter connections → subcortical/frontal-type dementia
- Fibres from the frontal micturition centres → urge incontinence
- Idiopathic (iNPH): majority of cases — diagnosis of exclusion
- Secondary: previous SAH, meningitis (↓ absorption capacity)
Classic clinical triad [1]:
-
Gait disturbance ("gait apraxia")
- Usually the earliest and most prominent feature — this helps distinguish NPH from Alzheimer's disease (where cognitive decline comes first) [5]
- Described as "glue-footed" — feet seem stuck to the ground, with difficult initiation, short shuffling steps, wide-based, magnetic gait, and instability [5]
- Pathophysiology: compression of periventricular motor fibres (especially those serving lower limbs, which are located medially)
- Can mimic parkinsonian gait — but there is no true rigidity or tremor
-
Cognitive decline (subcortical/frontal dementia)
- Psychomotor slowing, ↓ attention and concentration, impaired executive function, apathy [5]
- Unlike Alzheimer's disease, episodic memory is relatively preserved early on
- Pathophysiology: compression of frontal white matter connections
-
Urinary incontinence (urge-type)
- Usually the last component of the triad to appear
- Pathophysiology: disruption of frontal inhibitory pathways to the pontine micturition centre
"Need to distinguish from other causes of dementia such as AD, which does not respond to shunting" [1]
NPH vs Alzheimer's Disease — A High-Yield Comparison
| Feature | NPH | Alzheimer's Disease |
|---|---|---|
| First symptom | Gait disturbance | Memory loss |
| Dementia type | Subcortical/frontal | Cortical (aphasia, agnosia, apraxia) |
| Imaging | Ventriculomegaly >> sulcal effacement | Generalized atrophy with proportional sulcal widening |
| Treatable? | Yes — responds to CSF diversion! | No surgical cure |
| ICP signs | None (normal ICP) | None |
This distinction is critical because NPH is reversible with treatment [1][5].
Clinical Features
A. Acute Hydrocephalus (Adults)
This is essentially the clinical picture of acutely raised ICP superimposed on the specific features of hydrocephalus.
| Symptom | Pathophysiological Basis |
|---|---|
| Headache (supine > erect; worse early a.m.) [1] | Raised ICP is worse when supine (venous return to the brain increases in recumbency → ↑ intracranial blood volume → ↑ ICP). Early morning because ICP rises during sleep (↑ PaCO₂ from hypoventilation → cerebral vasodilation → ↑ blood volume) |
| Vomiting (might transiently relieve headache) [1] | Raised ICP stimulates the vomiting centre in the area postrema (floor of 4th ventricle). Vomiting transiently raises intrathoracic pressure → ↑ CSF drainage into the spinal canal → brief ICP reduction |
| Blurring of vision [1] | Papilloedema (if chronic enough) causes transient visual obscurations (TVOs) — fleeting episodes of grey-out/blurring lasting seconds, due to transient fluctuations in optic nerve head perfusion [6] |
| Diplopia (binocular, horizontal) [1] | CN VI (abducens) palsy — a "false localising sign." The abducens nerve has the longest intracranial course and is stretched over the petrous apex by diffuse raised ICP → lateral rectus paresis → convergent squint → horizontal diplopia |
| Deterioration in consciousness [1] | Raised ICP → ↓ CPP (CPP = MAP − ICP) → global cerebral ischaemia → reduced arousal. Also, if herniation occurs → brainstem compression → ↓ GCS |
| Nausea | Accompanies vomiting; stimulation of area postrema |
| Sign | Pathophysiological Basis |
|---|---|
| Papilloedema (late) [1] | ↑ ICP transmitted along the subarachnoid space surrounding the optic nerve sheath → "tourniquet" effect on the optic nerve → ↓ axoplasmic outflow → axonal swelling of the optic disc [6]. Note: papilloedema may take hours to days to develop and is therefore a late sign |
| Cushing's triad: Hypertension + Bradycardia + Irregular respiration [2] | A late and ominous sign. ↑ ICP → brainstem ischaemia (especially medulla) → sympathetic discharge (systemic HTN) → baroreceptor reflex (bradycardia) → respiratory centre dysfunction (irregular breathing). This is a sign of impending brainstem herniation |
| CN III, IV, VI palsy [2] | CN VI palsy is most common (longest intracranial course, as above). CN III palsy occurs with uncal herniation — the uncus herniates through the tentorial notch and compresses CN III → ipsilateral fixed, dilated pupil + ptosis + "down and out" eye |
| Impaired upward gaze (Parinaud's syndrome / "Sunset sign" in infants) [5] | Dilated 3rd ventricle or suprapineal recess compresses the dorsal midbrain (superior colliculus and pretectal area) → Parinaud's syndrome (upgaze paralysis, convergence-retraction nystagmus, light-near dissociation). In infants, this manifests as "sunsetting eyes" — lid retraction with impaired upward gaze so the sclera is visible above the iris [2][5] |
| UMN long tract signs [3] | Compression of periventricular white matter (corona radiata, internal capsule fibres) → upper motor neurone signs (hyperreflexia, spasticity, extensor plantar responses) |
| ↓ Consciousness → coma | Progressive compression of the reticular activating system (RAS) in the brainstem |
C. Infants and Young Children [1][2][5]
The presentation in infants is dramatically different because sutures and fontanelles are not yet fused → the cranial cavity is expansile [5]. This means:
- ICP may not rise significantly (the skull simply expands)
- Head size progressively enlarges
- Classic raised ICP signs are often absent or late
| Symptom | Pathophysiological Basis |
|---|---|
| Irritability [1][5] | Mild raised ICP and discomfort from expanding head |
| Vomiting | Stimulation of the area postrema by raised ICP |
| Failure to thrive, developmental delay [1][5] | Compression of developing brain parenchyma → impaired neurological development |
| Poor feeding | Combination of raised ICP and brainstem dysfunction |
| ↓ Conscious level (acute) [5] | If compensatory mechanisms overwhelmed → raised ICP → ↓ cerebral perfusion |
| Sign | Pathophysiological Basis |
|---|---|
| Macrocephaly (↑ head circumference) [1][2][5] | The unfused sutures and fontanelles allow the skull to expand as ventricular volume increases. Serial head circumference measurements crossing percentile lines is a key screening tool |
| Widely split sutures [2] | CSF pressure forces the cranial bones apart at the suture lines |
| Full or distended anterior fontanelle [1][2] | The anterior fontanelle is the largest and last to close (~18 months). Raised ICP causes it to bulge and feel tense on palpation |
| Frontal bossing [2] | Expansion of the frontal bones due to chronic raised pressure from within |
| Dilated and prominent scalp veins [1][2] | Raised intracranial venous pressure impedes venous drainage through the scalp → venous engorgement and distension of superficial scalp veins |
| Thin scalp [5] | Chronic stretching of the scalp over the expanding cranium |
| "Setting sun" sign [1][2][5] | Mechanism: pressure on midbrain tectum → Parinaud's syndrome [5]. Lid retraction + impaired upward gaze → the iris appears to "set" below the lower eyelid like a setting sun |
| "Cracked pot" sound on skull percussion [5] | Percussion of the skull produces a resonant "cracked pot" sound (Macewen's sign) due to separation of the cranial sutures with underlying fluid-filled ventricles |
| Accelerated pubertal development but disturbed growth [2] | Raised ICP or ventricular dilatation may compress the hypothalamus → disruption of GnRH pulsatility → precocious puberty. Growth disturbance may be due to compression of growth hormone pathways |
Infant vs Adult Hydrocephalus — Why the Difference?
The fundamental difference is skull compliance:
- Infants: open fontanelles and unfused sutures → skull can expand → head enlarges, ICP may remain relatively low
- Adults: fused skull → rigid container → any increase in volume rapidly raises ICP (Monro-Kellie doctrine)
This is why infants present with a big head and adults present with raised ICP symptoms.
Relevant Pathophysiology — Connecting the Dots
- Direct compression: Expanded ventricles compress the surrounding brain parenchyma, especially the periventricular white matter (corona radiata)
- Periventricular ischaemia: Compression of periventricular capillaries → local ischaemia → periventricular leukomalacia
- Transependymal CSF absorption: When ICP rises, CSF is forced through the ependymal lining into the periventricular extracellular space → interstitial oedema (periventricular lucencies on CT / hyperintensities on T2-FLAIR MRI) [3][5]
- ↓ Cerebral perfusion: ↑ ICP → ↓ CPP (CPP = MAP − ICP) → global cerebral ischaemia [5]
- Brain herniation: Pressure gradients across dural compartments → herniation syndromes → brainstem compression [5]
CPP = MAP − ICP (if ICP > JVP) CPP = MAP − JVP (if JVP > ICP)
This is the driving pressure for cerebral blood flow:
CBF = CPP / CVR = (MAP − ICP) / CVR [5]
Where CVR = cerebrovascular resistance.
Cerebral autoregulation maintains constant CBF across a range of MAP (roughly 50–150 mmHg in normotensive individuals). When ICP rises sufficiently to reduce CPP below the lower limit of autoregulation, CBF drops precipitously → cerebral ischaemia.
In chronic hypertension, the autoregulatory curve is shifted rightward — meaning these patients are vulnerable to ischaemia at higher MAPs than normotensive individuals [5].
In Hong Kong, the following aetiologies deserve particular emphasis:
-
TB meningitis: Hong Kong has an intermediate TB burden. TB meningitis causes basal meningeal exudates → obstruction of CSF flow at the basal cisterns and impaired absorption at arachnoid granulations → both communicating and obstructive hydrocephalus can occur. Hydrocephalus occurs in up to 80% of TB meningitis cases [7]
-
Cryptococcal meningitis: Seen in immunocompromised patients (HIV, transplant recipients). The gelatinous capsule of Cryptococcus neoformans clogs the arachnoid granulations → communicating hydrocephalus
-
Spontaneous SAH: From ruptured berry aneurysms. Blood in the subarachnoid space causes inflammation and fibrosis of arachnoid granulations → communicating hydrocephalus (acute or delayed)
-
Brain metastases: Common primary sites in HK include lung, breast, colorectal. Can cause obstructive hydrocephalus through mass effect
-
Nasopharyngeal carcinoma (NPC): While NPC itself does not typically cause hydrocephalus directly, extensive skull base invasion or leptomeningeal carcinomatosis can rarely do so
-
Post-neurosurgical: Any cranial surgery carries risk of post-operative hydrocephalus
| Obstructive (Non-communicating) | Communicating | |
|---|---|---|
| Acquired | Tumours: CPA tumours (vestibular schwannoma/meningioma), brain metastasis, gliomas, craniopharyngioma/pituitary macroadenoma, colloid cyst, pineal region tumours | Tumours: leptomeningeal carcinomatosis |
| Vascular: cerebellar infarct (with swelling), ICH, IVH | Vascular: SAH, IVH | |
| Infections: ventriculitis, post-infective aqueductal stenosis, brain abscess, neurocysticercosis | Infections: basal meningitis (TB, Cryptococcal) | |
| Normal pressure hydrocephalus | ||
| Congenital | Aqueductal stenosis, Dandy-Walker malformation, Arnold-Chiari (Type II) malformation, neural tube defects, congenital infections, congenital mass lesions | |
| Overproduction (rare) | Choroid plexus papilloma |
- Ventriculomegaly: enlargement of ventricles disproportionate to sulcal widening
- First ventricle to dilate: temporal horn of the lateral ventricles [3] — this is because the temporal horn is the thinnest-walled and most compliant portion
- Need to distinguish from hydrocephalus ex vacuo (physiological increase in ventricular volume with aging/cerebral atrophy) where ventriculomegaly is proportional to sulcal/cisternal widening [3][6]
- Periventricular lucencies (CT) / periventricular hyperintensities (T2/FLAIR MRI): due to transependymal oedema — CSF forced through the ependyma into periventricular white matter [3][5]
- Sulci and fissure effacement: expanded brain compresses the subarachnoid space [3]
- Midline shift / herniation: if asymmetric or associated mass lesion
- Pattern of ventricular dilatation helps localise the obstruction:
- All ventricles dilated → communicating hydrocephalus
- Lateral + 3rd ventricle dilated, 4th ventricle normal → aqueductal obstruction
- One lateral ventricle dilated → foramen of Monro obstruction on that side
High Yield Summary
Definition: Accumulation of excess CSF within the cranium → ventricular dilatation ± raised ICP
CSF Dynamics: Produced at choroid plexus (~450 mL/day), circulates through ventricles → subarachnoid space, absorbed at arachnoid granulations into superior sagittal sinus
Classification (CRITICAL):
- Obstructive (non-communicating): blockage WITHIN ventricular system → LP CONTRAINDICATED
- Communicating: impaired absorption OUTSIDE ventricular system → LP safe and therapeutic
- NPH: chronic communicating hydrocephalus with normal ICP, classic triad of gait disturbance → dementia → incontinence, surgically treatable
Causes:
- Congenital: aqueductal stenosis, Dandy-Walker, Chiari II, neural tube defects
- Acquired: tumours, SAH, meningitis (TB, bacterial, cryptococcal), ICH/IVH
Clinical Features:
- Adults (acute): raised ICP symptoms (headache worse supine/AM, vomiting, visual blurring, CN VI palsy, ↓ consciousness, papilloedema)
- Adults (chronic/NPH): Adam's triad — gait apraxia, dementia, incontinence (NO raised ICP symptoms)
- Infants: macrocephaly, tense fontanelle, split sutures, scalp vein dilatation, setting sun sign, developmental delay
Key Equations: CPP = MAP − ICP; CBF = CPP/CVR
NPH vs Alzheimer's: Gait first in NPH vs memory first in AD; NPH responds to shunting; imaging shows ventriculomegaly >> sulcal effacement in NPH
Active Recall - Hydrocephalus
[1] Lecture slides: GC 111. Raised intracranial pressure and hydrocephalus.pdf (p14–16) [2] Senior notes: felixlai.md (Hydrocephalus section) [3] Senior notes: maxim.md (Section 5.3 Hydrocephalus) [4] WHO global estimates of congenital hydrocephalus incidence [5] Senior notes: Ryan Ho Neurology.pdf (p153, p159–160) [6] Senior notes: Ryan Ho Opthalmology.pdf (p90 — Papilloedema) [7] Senior notes: Ryan Ho Respiratory.pdf (p79–80 — TB meningitis)
The differential diagnosis of hydrocephalus operates on two levels. First, when you encounter the clinical syndrome (raised ICP symptoms, or the triad of gait-dementia-incontinence, or an infant with a big head), you need to consider what else could cause those presentations besides hydrocephalus. Second, once hydrocephalus is confirmed on imaging, you need to determine the underlying aetiology — because hydrocephalus itself is a syndrome, not a final diagnosis.
Let's work through both systematically.
Level 1: What Else Mimics the Clinical Presentation of Hydrocephalus?
The presentation of hydrocephalus varies dramatically by age and acuity. The differential diagnosis therefore depends on which clinical syndrome you are dealing with.
When a patient presents with headache (supine > erect; worse early a.m.), vomiting, blurring of vision, diplopia (CN VI), deterioration in consciousness, and papilloedema [1], you must consider all causes of raised ICP — not just hydrocephalus.
| Differential | Key Distinguishing Features | Why It Mimics Hydrocephalus |
|---|---|---|
| Space-occupying mass lesion (haematoma, tumour, abscess) [1] | Focal neurological deficit, seizures, constitutional symptoms (tumour), fever (abscess), trauma history (haematoma) | All raise ICP via the Monro-Kellie doctrine — increasing the volume of intracranial contents in a rigid skull. CT/MRI differentiates by showing the mass rather than ventricular dilatation |
| Brain swelling — focal/diffuse (cerebral oedema) [1] | History of ischaemic stroke (large territory infarction), trauma, hypoxic-ischaemic encephalopathy | Cytotoxic and vasogenic oedema increase brain parenchymal volume → raised ICP. Imaging shows diffuse swelling or territorial oedema rather than ventriculomegaly |
| Hyperaemia [1] | Post-traumatic, post-ischaemic reperfusion | Increased cerebral blood volume in the rigid skull raises ICP. Rare as an isolated cause |
| Venous congestion [1] | Cerebral venous sinus thrombosis (CVST): headache, seizures, focal deficits, papilloedema. Risk factors include pregnancy, OCP, prothrombotic states | Venous outflow obstruction → ↑ venous blood volume → ↑ ICP AND ↓ CSF absorption (venous pressure exceeds CSF pressure at arachnoid granulations). MR venogram shows filling defect (empty delta sign in SSS thrombosis) [8] |
| Intracranial haemorrhage (SAH, ICH, EDH, SDH) | SAH: thunderclap headache, meningism. ICH: acute focal deficit + headache. EDH: lucid interval post-trauma. SDH: subacute/chronic progressive | Each raises ICP through different mechanisms (mass effect, blood in subarachnoid space). Note that SAH and IVH can cause secondary hydrocephalus [9][10] |
| Meningitis / Encephalitis | Fever, meningism, altered sensorium, photophobia | Infection causes cerebral oedema (→ raised ICP) AND can cause hydrocephalus secondarily through inflammatory obstruction of CSF pathways [7] |
| Idiopathic intracranial hypertension (IIH / pseudotumour cerebri) [5] | Obese young woman, papilloedema, visual obscurations, CN VI palsy, pulsatile tinnitus. Normal brain parenchyma on imaging with small/"slit" ventricles, empty sella sign | Raised ICP without a mass lesion or ventriculomegaly. The key distinguishing feature: IIH has small or normal ventricles whereas hydrocephalus has dilated ventricles. LP shows ↑ opening pressure but normal constituents [5] |
Key point from lecture slides: The common causes of raised ICP listed are: space-occupying mass lesion (haematoma, tumour, abscess), hydrocephalus (communicating/non-communicating), brain swelling (focal/diffuse), hyperaemia, and venous congestion [1]
IIH vs Hydrocephalus — A Common Exam Pitfall
Both IIH and hydrocephalus cause raised ICP symptoms (headache, papilloedema, CN VI palsy). The critical distinction is on imaging:
- IIH: small or normal ventricles, empty sella, no mass
- Hydrocephalus: dilated ventricles, periventricular oedema
Never diagnose hydrocephalus without confirming ventriculomegaly on imaging. Conversely, never diagnose IIH without ruling out hydrocephalus and intracranial mass first [5].
This is perhaps the higher-yield differential for clinical exams. NPH must be distinguished from other causes of dementia because it responds well to CSF diversion [1][5].
| Differential | Key Distinguishing Features | Why It Mimics NPH |
|---|---|---|
| Alzheimer's disease (AD) [1][5][11] | Cognitive decline (memory) is the FIRST and most prominent feature — insidious anterograde amnesia with later cortical signs (aphasia, apraxia, agnosia). Gait disturbance occurs late. Imaging: generalised cerebral atrophy with proportional ventricular enlargement and sulcal widening (i.e. hydrocephalus ex vacuo) | Both present with dementia in the elderly. Critical distinction: in NPH, gait disturbance occurs early whereas in AD, cognitive features come first [5]. Imaging in AD shows atrophy proportional to ventricular size; in NPH, ventricular enlargement >> sulcal effacement [5][11] |
| Vascular dementia (VaD) [11] | Stepwise deterioration, prior cardiovascular risk factors, evidence of prior strokes on imaging, labile mood, preserved insight | Both cause gait disturbance and cognitive decline. VaD has a stepwise course and clear vascular lesions on MRI. NPH has an insidious course |
| Parkinson's disease / Parkinsonism [5] | Resting tremor, rigidity, bradykinesia (cardinal triad). Gait is shuffling but with festination and flexed posture rather than the wide-based "magnetic" gait of NPH | The shuffling gait can superficially resemble NPH. Key: PD has true rigidity, resting tremor, and good response to levodopa. NPH gait is wide-based, "glue-footed" with difficult initiation but without true parkinsonian features |
| Pseudoparkinsonism — cerebral arteriosclerotic disease [12] | Stepwise deterioration, LL > UL involvement, more symmetrical, poor response to levodopa | Subcortical vascular disease can mimic both PD and NPH. Distinguished by imaging (multiple lacunar infarcts in basal ganglia/white matter) |
| Dementia with Lewy Bodies (DLB) [11] | Fluctuating cognition, visual hallucinations, parkinsonism, REM sleep behaviour disorder, neuroleptic sensitivity | Both cause cognitive decline with motor features. DLB has prominent psychiatric symptoms (VH, fluctuations) which are absent in NPH [11] |
| Frontotemporal dementia (FTD) | Behavioural variant: personality changes, disinhibition, antisocial behaviour. Language variant: progressive aphasia. Onset often younger (< 65) | Both are "anterior" dementias with executive dysfunction. FTD has prominent behavioural changes which are disproportionate in NPH |
| Chronic subdural haematoma (CSDH) [8] | History of trauma (may be minor/forgotten, especially in elderly on anticoagulants). Fluctuating consciousness, focal deficits, headache. Crescentic hypodensity on CT | Both cause progressive cognitive decline and gait instability in the elderly. CT distinguishes: CSDH shows an extra-axial collection; NPH shows ventriculomegaly |
| Depression ("pseudodementia") [11] | More well-defined onset, patient complains actively about poor memory (vs NPH patients often lack insight), less effort in testing, no gait apraxia, classical depressive features | Apathy and psychomotor slowing in NPH can resemble depression. A therapeutic trial of antidepressants may be warranted before concluding NPH |
| Cervical myelopathy / Spinal cord disease | UMN signs in limbs (spasticity, hyperreflexia), bladder dysfunction, sensory level. MRI spine shows cord compression | Can cause gait difficulty and incontinence (2 of 3 NPH triad components). Distinguished by presence of a sensory level and spinal imaging |
| B12 deficiency (subacute combined degeneration) | Peripheral neuropathy, posterior column signs (loss of proprioception/vibration), macrocytic anaemia | Can cause gait ataxia, cognitive decline, and incontinence. Serum B12 and methylmalonic acid levels are diagnostic |
Hydrocephalus Ex Vacuo — Not True Hydrocephalus!
Hydrocephalus ex vacuo refers to the physiological increase in ventricular volume that occurs with aging and/or cerebral atrophy (e.g., in Alzheimer's disease) [3]. The ventricles enlarge passively to fill the space left by shrinking brain tissue. This is NOT hydrocephalus because:
- There is no CSF flow obstruction or absorption impairment
- Ventricular enlargement is proportional to sulcal widening (both expand together)
- ICP is normal
- There is no transependymal oedema (no periventricular lucencies)
In true hydrocephalus (including NPH), ventricular enlargement is disproportionately large compared to sulcal widening — the ventricles are big but the sulci are effaced [3][5].
When an infant presents with a progressively enlarging head, consider:
| Differential | Key Distinguishing Features |
|---|---|
| Hydrocephalus (any cause) | Tense fontanelle, split sutures, setting sun sign, dilated scalp veins, irritability. Confirmed by cranial USS or CT/MRI showing ventriculomegaly |
| Familial/constitutional macrocephaly (benign) | Family history of large heads, normal development, normal fontanelle tension, normal imaging. Head circumference follows a high but parallel percentile |
| Megalencephaly | Abnormally large brain (not enlarged ventricles). Can be benign or associated with syndromes (Sotos syndrome, Alexander disease, Canavan disease) |
| Subdural effusion / haematoma | Post-traumatic or post-meningitic. Imaging shows extra-axial fluid collection, not ventriculomegaly. Consider non-accidental injury |
| Thickened skull (cranial hyperostosis) | Rare. Conditions like osteopetrosis, rickets, thalassaemia (marrow expansion). Skull X-ray/CT shows bony thickening |
| Storage diseases (mucopolysaccharidoses) | Coarse facies, hepatosplenomegaly, skeletal dysplasia, developmental regression |
Level 2: Determining the Underlying Aetiology Once Hydrocephalus Is Confirmed
Once imaging confirms hydrocephalus (ventriculomegaly ± periventricular oedema), the next step is to determine why. The pattern of ventricular dilatation and the clinical context guide you.
By temporal profile (this helps narrow the differential rapidly):
| Acuity | Common Causes | Why This Temporal Profile? |
|---|---|---|
| Hyperacute / Acute (hours–days) | IVH, acute SAH, posterior fossa haemorrhage, acute bacterial meningitis, acute tumour haemorrhage, colloid cyst (intermittent) | Sudden blockage of CSF pathways or acute inflammation → rapid accumulation. The rate of CSF production (~0.3 mL/min) means significant ventriculomegaly develops within hours if outflow is completely blocked |
| Subacute (days–weeks) | TB meningitis (hydrocephalus in ~80% of TBM [7]), brain abscess, growing tumour, cryptococcal meningitis | Slower obstruction or progressive inflammatory damage to arachnoid granulations |
| Chronic (weeks–months–years) | NPH, slow-growing tumours (meningioma, craniopharyngioma), aqueductal stenosis (compensated), post-SAH/meningitis (late fibrosis) | Gradual ventricular enlargement with partial compensation. In NPH, the brain "accommodates" to enlarged ventricles — ICP normalises but parenchymal damage continues through mechanical compression of corona radiata [5] |
| Congenital | Aqueductal stenosis, Arnold-Chiari malformation, Dandy-Walker syndrome, neural tube defect, congenital infection, congenital mass lesions [1] | Developmental abnormalities present from birth. Detected antenatally on USS or in early infancy with macrocephaly |
Specific High-Yield Aetiologies to Differentiate
SAH is a major cause of both acute and delayed hydrocephalus. The mechanisms differ by timing:
- Acute (within days): Blood clot in the ventricles (IVH) or basal cisterns physically obstructs CSF flow → obstructive hydrocephalus. Blood in the subarachnoid space also acutely impairs arachnoid granulation function
- Delayed/chronic (weeks–months): Fibrosis and adhesion formation at arachnoid granulations from blood breakdown products → communicating hydrocephalus. May require permanent shunting
Clinical management pathway [9]: SAH → secure aneurysm (clip/coil) → ICU care → CSF shunting for hydrocephalus as a known complication
Arteriovenous malformations (AVMs) can cause hydrocephalus through several mechanisms [10]:
- Direct mass effect on ventricular system
- Haemorrhage (IVH/SAH) obstructing CSF pathways
- High-flow shunting raising venous sinus pressure → impaired CSF absorption
- Listed as a clinical feature of AVM: hydrocephalus [10]
- TB meningitis causes hydrocephalus in ~80% of cases [7]
- Mechanism: thick basal exudates block CSF flow at the basal cisterns (obstructive component) AND cause arachnoid granulation inflammation/fibrosis (communicating component)
- Can be both acute and chronic
- Imaging: basal meningeal enhancement, hydrocephalus, periventricular infarcts [7]
This is a critical radiological differential:
| Feature | True Hydrocephalus | Hydrocephalus Ex Vacuo (Cerebral Atrophy) |
|---|---|---|
| Ventriculomegaly | Disproportionately large compared to sulci | Proportional to sulcal/cisternal widening [3][6] |
| Sulci | Effaced (compressed against skull) | Widened (brain shrinkage) |
| Periventricular lucencies | Present (transependymal oedema) | Absent |
| Temporal horns | Dilated (first to dilate) [3] | May be mildly enlarged |
| 3rd ventricle | Ballooned with convex lateral walls | Normal or mildly enlarged |
| Clinical context | Signs of raised ICP or NPH triad | Progressive cognitive decline without gait/incontinence |
| Response to CSF diversion | Yes (in appropriate cases) | No |
From lecture slides — diagnosis of hydrocephalus relies on: clinical suspicion, imaging studies (ventricular dilatation, change in morphology and periventricular oedema), MRI CSF studies, lumbar puncture (measures CSF pressure, trial drainage — BUT BE CAREFUL!!), EVD (rarely) [1]
When you encounter a patient where hydrocephalus is in the differential, work through this logical sequence:
Critical Safety Distinction — Reiterated
A Critical Distinction from the lecture slides [1]:
- Communicating hydrocephalus (e.g., recent SAH, 4th ventricle patent): LP is diagnostic and therapeutic
- Non-communicating hydrocephalus (e.g., cerebellar tumour + 4th ventricular obstruction, colloid cyst in 3rd ventricle): LP is absolutely contraindicated (and lethal)
Always confirm the type on imaging before proceeding. If in doubt, use EVD as a temporising measure [1].
| Presentation | Top Differentials to Consider |
|---|---|
| Acute raised ICP | Intracranial mass (tumour, abscess, haematoma), cerebral oedema (stroke, trauma), SAH, CVST, acute hydrocephalus, IIH |
| Chronic gait-dementia-incontinence | NPH, Alzheimer's disease, vascular dementia, Parkinson's disease/DLB, chronic subdural haematoma, cervical myelopathy, B12 deficiency, depression |
| Infant macrocephaly | Hydrocephalus (congenital causes), benign familial macrocephaly, megalencephaly, subdural effusion/haematoma, storage diseases |
| Ventriculomegaly on imaging | True hydrocephalus (communicating or obstructive) vs hydrocephalus ex vacuo (cerebral atrophy) |
High Yield Summary
The differential of hydrocephalus operates at two levels:
-
Clinical syndrome mimics — What else causes raised ICP (acute) or gait-dementia-incontinence (chronic)?
- Acute: mass lesion, cerebral oedema, CVST, IIH (key distinguisher: IIH has small ventricles, hydrocephalus has large ventricles)
- Chronic (NPH): Alzheimer's disease (memory first, proportional atrophy on imaging), vascular dementia (stepwise), PD (tremor/rigidity), DLB (hallucinations), CSDH, depression
-
Aetiological differential once confirmed — Communicating vs obstructive, determined by whether the 4th ventricle is dilated
- Communicating: SAH, meningitis, leptomeningeal carcinomatosis, NPH, choroid plexus papilloma
- Obstructive: tumours, aqueductal stenosis, Dandy-Walker, Chiari, colloid cyst, IVH
Critical distinction: LP is safe in communicating hydrocephalus; LP is contraindicated and lethal in non-communicating hydrocephalus.
NPH is the "must-not-miss" diagnosis because it is a surgically treatable cause of cognitive decline that mimics irreversible dementias.
Hydrocephalus ex vacuo is NOT true hydrocephalus — ventricular enlargement is proportional to sulcal widening from atrophy, with no periventricular oedema.
Active Recall - Hydrocephalus Differential Diagnosis
[1] Lecture slides: GC 111. Raised intracranial pressure and hydrocephalus.pdf (p2, p14–18) [3] Senior notes: maxim.md (Section 5.3 Hydrocephalus) [5] Senior notes: Ryan Ho Neurology.pdf (p58–60, p153, p158–160) [6] Senior notes: Ryan Ho Opthalmology.pdf (p90) [7] Senior notes: Ryan Ho Respiratory.pdf (p79–80) [8] Senior notes: Ryan Ho Radiology.pdf (p20–21) [9] Lecture slides: GC 109. Headache and loss of consciousness Acute stroke, subarachnoid haemorrhage and vascular malformation.pdf (p21) [10] Lecture slides: GC 109. Headache and loss of consciousness Acute stroke, subarachnoid haemorrhage and vascular malformation.pdf (p23) [11] Senior notes: Ryan Ho Psychiatry.pdf (p81–82, p88, p95) [12] Senior notes: Ryan Ho Neurology.pdf (p120)
Hydrocephalus does not have a single universally agreed-upon "diagnostic criteria" checklist like, say, the McDonald criteria for MS. Instead, diagnosis is based on the convergence of clinical suspicion, neuroimaging findings, and — in selected cases — CSF dynamics testing. Let's break each component down from first principles.
The Diagnostic Triad: Clinical + Imaging + CSF Dynamics
The diagnosis of hydrocephalus rests on three pillars [1]:
- Clinical suspicion — appropriate symptoms and signs
- Imaging studies — ventricular dilatation, change in morphology and periventricular oedema [1]
- CSF dynamics assessment — MRI CSF studies, lumbar puncture (measures CSF pressure, trial drainage — BUT BE CAREFUL!!) [1], or EVD (rarely) [1]
The relative importance of each pillar shifts depending on whether you're dealing with acute hydrocephalus (where imaging is diagnostic and LP is often unsafe) or NPH (where imaging is suggestive but CSF dynamics testing provides the clinching evidence).
For acute hydrocephalus, the diagnosis is essentially clinical + imaging:
| Criterion | Details |
|---|---|
| Clinical | Signs and symptoms of raised ICP: headache (supine > erect, worse early a.m.), vomiting, blurring of vision and diplopia (CN VI), deterioration in consciousness, papilloedema (late) [1]. In infants: large head, dilated scalp veins, tense fontanelle, sunset eyes, irritability, development delay [1] |
| Imaging | CT or MRI showing ventriculomegaly with features distinguishing it from cerebral atrophy (see below) |
| Additional | ICP measurement (via EVD or LP in communicating cases) confirms raised pressure, but is not required for diagnosis — it is more for monitoring and treatment |
Normal Pressure Hydrocephalus — Diagnostic Criteria (More Structured)
NPH requires more rigorous diagnostic workup because the clinical picture overlaps heavily with other dementias. The 2005 International NPH Guidelines (Relkin, Marmarou et al.) remain the standard framework, refined by the 2020 Japanese NPH Guidelines (3rd edition):
All of the following must be met:
- Trial drainage: external lumbar drainage of CSF (40–100 mL) to test for clinical improvement [5] — this is arguably the most important diagnostic manoeuvre
- CSF flow study for difficult cases [5] — phase-contrast MRI showing hyperdynamic CSF flow through the aqueduct
- Positive response to extended lumbar drainage (72-hour continuous drainage)
The Tap Test — Why It Works
The CSF tap test (large-volume LP removing 30–50 mL) is a diagnostic AND prognostic tool for NPH. The rationale: if removing CSF temporarily improves the patient's gait or cognition, this predicts a good response to permanent CSF diversion (shunting). Assess gait speed and cognitive testing (e.g., Mini-Mental State Examination, timed up-and-go test) before and after the LP.
- Sensitivity: only ~50–60% (i.e., a negative tap test does NOT rule out NPH — many patients still improve with shunting)
- Specificity: ~90% (a positive response strongly predicts shunt-responsiveness)
For equivocal cases, extended lumbar drainage (continuous drainage over 72 hours via a lumbar catheter) has higher sensitivity (~80–90%) [5].
Key Imaging Indices and Measurements
Evans' index = maximum width of the frontal horns / maximum biparietal diameter of the inner skull, measured on the same axial slice.
- Normal: < 0.3
- Hydrocephalus: Evans' index > 0.3 indicates ventriculomegaly
Why it works: the frontal horns are among the first parts of the lateral ventricles to dilate in hydrocephalus. Comparing them to the biparietal diameter normalises for head size.
Evans' Index — Necessary but Not Sufficient
Evans' index > 0.3 confirms ventriculomegaly but does NOT by itself distinguish true hydrocephalus from hydrocephalus ex vacuo (cerebral atrophy). You MUST look at additional features — particularly the relationship between ventricular size and sulcal widening, and the presence of periventricular oedema.
A highly specific finding for iNPH on imaging:
- Ventriculomegaly (Evans' index > 0.3) WITH
- Tight high-convexity sulci (effaced at the vertex/medial surface) AND
- Widened Sylvian fissures (laterally)
Why this pattern? In NPH, the enlarged ventricles push brain tissue upward and outward → the superior convexity sulci are compressed against the skull, while the Sylvian fissures (which are more compliant) remain dilated. This "top-tight, bottom-wide" pattern is characteristic and distinguishes NPH from atrophy (where sulci are widened everywhere).
Investigation Modalities — Detailed Breakdown
Why CT first? It is fast (< 5 minutes), widely available (even at 3am in any Emergency Department), and excellent at detecting acute hydrocephalus, haemorrhage, and mass lesions. In the acute setting, a non-contrast CT brain is the single most important investigation.
Key findings in hydrocephalus on CT [3][5][6]:
| Finding | Description | Pathophysiological Basis |
|---|---|---|
| Ventriculomegaly | Enlarged ventricles with rounded (ballooned) temporal and frontal horns [5] | CSF accumulation under pressure stretches the normally angular ventricular horns into smooth, rounded contours |
| First ventricle to dilate: temporal horn of lateral ventricles [3] | The temporal horns are normally slit-like; even mild dilatation is pathological | The temporal horn walls are thin and compliant — they offer the least resistance to expansion |
| Periventricular lucencies (hypodensities) [3][5] | Halo of low density surrounding the ventricles, especially at the frontal and occipital horns | Transependymal oedema — when ventricular pressure exceeds the absorptive capacity of the ependyma, CSF is forced through the ependymal lining into the periventricular white matter [5] |
| Sulci and fissure effacement [3] | Cortical sulci appear compressed/absent over the convexity | Expanded ventricles push the brain parenchyma outward against the inner skull table, compressing the subarachnoid space |
| Midline shift / herniation [3] | Asymmetric ventricular dilatation (e.g., unilateral foramen of Monro obstruction) or associated mass effect | Unequal pressure between hemispheres causes the brain to shift across the midline |
| Evans' index > 0.3 | Measured on axial slice at level of frontal horns | See above — quantitative confirmation of ventriculomegaly |
| Obstructive hydrocephalus pattern: not all ventricles dilated, 4th ventricle normal-looking [5] | Proximal ventricles dilated, distal ventricles normal | Obstruction is within the ventricular system; ventricles downstream of the block are decompressed |
Distinguishing from cerebral atrophy (hydrocephalus ex vacuo) [3][6]:
Why MRI? Superior soft tissue contrast, multiplanar imaging, and specific sequences provide far more detail than CT. MRI is the imaging modality of choice for:
- Identifying the site and cause of obstruction (especially posterior fossa lesions, aqueductal stenosis, tumours)
- Assessing periventricular oedema (best on T2-weighted FLAIR)
- CSF flow studies (phase-contrast MRI)
- Evaluating NPH (DESH sign, aqueductal flow void)
- Ruling out differentials (e.g., CVST on MR venography)
Key MRI sequences and findings:
| Sequence | Findings in Hydrocephalus | Why This Sequence? |
|---|---|---|
| T1-weighted | Enlarged ventricles (CSF appears dark/hypointense); mass lesion identification | Basic anatomical delineation |
| T2-weighted | Enlarged ventricles (CSF appears bright/hyperintense); periventricular hyperintensity = transependymal oedema | Fluid-sensitive — highlights CSF and oedema |
| T2-FLAIR | Periventricular radiolucency (hyperintensity) especially on FLAIR sequence [5][11] — this is the most sensitive sequence for periventricular oedema | FLAIR "nulls" free-flowing CSF (makes it dark) while keeping oedema bright — so periventricular oedema stands out against the dark CSF in the ventricles. Brilliantly useful for distinguishing transependymal oedema from normal CSF |
| Sagittal T2 | Visualises the aqueduct of Sylvius — "flow void" (dark signal) indicates patent aqueduct with flowing CSF; absent flow void suggests stenosis. Also shows Chiari malformation, 3rd ventricle floor anatomy for ETV planning | Best single sequence for determining the SITE of obstruction |
| Phase-contrast (cine) MRI | MRI CSF studies [1] — quantifies CSF flow velocity and direction through the aqueduct over the cardiac cycle. In NPH: hyperdynamic aqueductal CSF flow (aqueductal stroke volume > 42 μL is suggestive). In aqueductal stenosis: absent or markedly reduced flow | Non-invasive assessment of CSF dynamics; helpful in difficult NPH cases [5] |
| DWI | Can show restricted diffusion in periventricular white matter (acute hydrocephalus with ischaemia) or in associated pathology (abscess, infarct) | Helps identify complications and exclude differentials |
| Contrast-enhanced T1 | Identifies tumours, meningeal enhancement (meningitis, leptomeningeal carcinomatosis), ring-enhancing lesions | Essential for aetiological workup — what is CAUSING the hydrocephalus? |
| MR Venography | Rules out cerebral venous sinus thrombosis (CVST) which can cause communicating hydrocephalus by raising venous pressure | Important differential; CVST can look very similar to IIH or communicating hydrocephalus |
Why FLAIR Is the Key Sequence
On standard T2-weighted images, both CSF and periventricular oedema appear bright (hyperintense) — making it difficult to distinguish oedema from normal CSF. FLAIR (Fluid-Attenuated Inversion Recovery) selectively suppresses the signal from free-flowing CSF while keeping oedema signal bright. This means periventricular oedema "lights up" as a bright halo around the otherwise dark ventricles — a highly specific sign of active hydrocephalus (transependymal CSF migration) [5][11].
LP measures CSF pressure and allows trial drainage — BUT BE CAREFUL!! [1]
This is simultaneously one of the most useful and most dangerous investigations in hydrocephalus. The safety depends entirely on whether the hydrocephalus is communicating or non-communicating:
| Communicating Hydrocephalus | Non-communicating Hydrocephalus | |
|---|---|---|
| Safety | LP is diagnostic and therapeutic [1] | LP is absolutely contraindicated (and lethal) [1] |
| Why? | CSF freely communicates between ventricles and lumbar space → removing CSF below reduces pressure evenly throughout the system | Ventricular CSF is isolated from lumbar space → removing CSF below creates a pressure gradient across the tentorium/foramen magnum → downward herniation |
| Application | Measure opening pressure, perform CSF tap test (remove 30–50 mL and assess clinical improvement), obtain CSF for analysis (infection, malignancy) | Do NOT perform LP; use EVD instead for CSF diversion and ICP monitoring |
"No LP if raised ICP unless absolutely sure communicating hydrocephalus" [1]
LP findings in hydrocephalus (when safe to perform):
| Parameter | Finding | Interpretation |
|---|---|---|
| Opening pressure | Elevated ( > 20 cmH₂O) in acute communicating hydrocephalus; normal (6–20 cmH₂O) in NPH | In NPH, pressure is paradoxically normal — the damage comes from the enlarged ventricular surface area (Force = Pressure × Area), not from the pressure itself |
| CSF composition | May reveal the underlying cause: ↑ protein + ↓ glucose + lymphocytic pleocytosis in TB meningitis [7]; ↑ cryptococcal Ag in cryptococcal meningitis [13]; malignant cells in leptomeningeal carcinomatosis | Always send CSF for biochemistry, cell count, culture, and cytology when the aetiology is unclear |
| Post-LP clinical improvement | Improvement in gait/cognition after removing 30–50 mL → positive tap test predicting good shunt response | This is the therapeutic trial for NPH [5] |
- External Ventricular Drain (EVD): gold standard for ICP monitoring. A catheter is placed directly into the lateral ventricle through a burr hole. Allows both continuous ICP measurement and therapeutic CSF drainage
- Intraparenchymal pressure monitor: fibreoptic catheter placed in brain parenchyma. Measures ICP but cannot drain CSF
- LP (in communicating cases only): intermittent measurement of opening pressure
When to use ICP monitoring [1]:
Why USS in infants? The open anterior fontanelle provides an acoustic window that allows direct visualisation of the ventricles without radiation or sedation.
| Advantage | Limitation |
|---|---|
| Bedside, non-invasive, no radiation, no sedation | Limited to infants with open fontanelle (typically < 18 months) |
| Can be repeated serially for monitoring | Cannot visualise posterior fossa well; limited parenchymal detail |
Key findings: dilated lateral ventricles, dilated 3rd ventricle, periventricular echogenicity (oedema)
When? A patient with a known VP/VA shunt presenting with new symptoms of hydrocephalus (suggesting shunt malfunction).
What it involves: plain X-rays of the entire course of the shunt — skull XR, C-spine XR, CXR, AXR [3]
Key findings [3]:
- Shunt disconnection/fracture: visible break in the catheter line
- Catheter migration/dislodgement: tip not in expected position
- Kinking: catheter looped or angulated
This is a quick first-line investigation to identify mechanical shunt failure before proceeding to CT brain for ventricular assessment.
Why? To detect papilloedema — optic disc swelling caused by raised ICP transmitted along the optic nerve sheath [6].
- Acute papilloedema: swollen disc with blurred margins, dilated superficial capillaries, absent spontaneous venous pulsation
- Chronic papilloedema: optic atrophy, constricted visual fields → permanent vision loss if untreated
Key points [6]:
- Papilloedema is a late sign [1] — its absence does NOT exclude raised ICP
- In infants, papilloedema may not develop (expandable skull decompresses ICP)
- Always perform fundoscopy before LP to help assess for raised ICP
Once hydrocephalus is confirmed and classified (communicating vs obstructive), targeted investigations identify the aetiology:
| Suspected Cause | Investigation | Key Findings |
|---|---|---|
| Tumour | Contrast MRI brain | Enhancing mass at specific location (posterior fossa, pineal, sellar, CPA); associated oedema [13a] |
| SAH | Non-contrast CT brain (acute); LP for xanthochromia (if CT negative); CTA/MRA/DSA for aneurysm | Hyperdensity in basal cisterns and sulcal spaces [8]; CSF shunting for post-SAH hydrocephalus [9] |
| TB meningitis | Contrast CT/MRI: basal meningeal enhancement, tuberculoma, hydrocephalus, periventricular infarcts [7]. CSF: ↑ protein, ↓ glucose, lymphocytic pleocytosis, AFB smear/culture, TB-PCR, ADA | Hydrocephalus in ~80% of TBM [7] |
| Cryptococcal meningitis | LP (safe — communicating): ↑ protein, ↓ glucose, lymphocytes. Indian ink stain, CSF/serum cryptococcal antigen | Communicating hydrocephalus from gelatinous capsule clogging arachnoid granulations [13] |
| Bacterial meningitis | Blood cultures, LP (after CT if indicated), CSF Gram stain/culture | Post-meningitic arachnoid granulation adhesions → communicating hydrocephalus |
| Congenital causes | MRI brain (sagittal views critical): aqueductal stenosis (absent aqueductal flow void on cine MRI), Chiari malformation (tonsillar descent), Dandy-Walker (cystic 4th ventricle, absent vermis) | Prenatal USS may show ventriculomegaly |
| Leptomeningeal carcinomatosis | Contrast MRI (leptomeningeal enhancement), CSF cytology (malignant cells), CSF flow cytometry | Communicating hydrocephalus; may need repeated LP for cytology (sensitivity improves with repeat sampling) |
| CVST | MR venography (filling defect, absent flow) | Empty delta sign in SSS thrombosis; may cause communicating hydrocephalus via raised venous pressure |
NPH-Specific Diagnostic Workup — Step-by-Step
Because NPH is a surgically treatable cause of cognitive decline [1] that must not be missed, and because the diagnosis is challenging, here is the structured approach:
- Age > 60, at least 2 of: gait disturbance, cognitive decline, urinary incontinence
- Gait assessment: timed up-and-go (TUG) test, 10-metre walk test — quantify for pre/post comparison
- Cognitive assessment: MMSE or MoCA (look for subcortical pattern: slow processing, poor attention, impaired executive function)
- Rule out other causes: check B12, TFT, RFT, Ca, glucose (reversible causes of dementia) [11]
- MRI preferred over CT [5]:
- Ventricular enlargement >> sulcal effacement [5]
- Evans' index > 0.3
- DESH sign (tight high-convexity, wide Sylvian fissure)
- Periventricular radiolucency especially on T2 FLAIR sequence [5]
- Aqueductal flow void present (excludes aqueductal stenosis)
- Phase-contrast cine MRI: hyperdynamic aqueductal CSF flow (aqueductal stroke volume > 42 μL)
- Trial drainage: external lumbar drainage of CSF (40–100 mL) to test for clinical improvement [5]
- Practical protocol: LP, remove 30–50 mL CSF, measure opening pressure
- Assess gait (TUG, 10-metre walk) and cognition at baseline, then at 1 hour, 24 hours, and 72 hours post-LP
- Positive test: ≥ 20% improvement in gait speed or ≥ 3-point improvement in MMSE
- Continuous lumbar CSF drainage via an indwelling lumbar catheter over 72 hours, draining ~150–200 mL total
- Higher sensitivity (~80–90%) than single tap test
- Requires inpatient monitoring (risk of overdrainage, infection, nerve root irritation)
- Phase-contrast cine MRI quantifying aqueductal stroke volume
- Resistance to CSF outflow (Rout) measured via infusion test (research-level; infrequently used in HK clinical practice)
| Investigation | When to Use | Key Finding | Safety Considerations |
|---|---|---|---|
| NCCT brain | First-line, acute | Ventriculomegaly, periventricular lucency, mass, haemorrhage | Safe, rapid |
| MRI brain | Gold standard, detailed assessment | All CT findings + aqueductal assessment, DESH, FLAIR oedema, cause identification | Requires time and cooperation; check programmable shunt settings before and after [1] |
| MRI CSF studies (cine MRI) [1] | NPH workup, difficult cases | Hyperdynamic aqueductal flow, aqueductal stroke volume | Non-invasive |
| LP [1] | Communicating hydrocephalus ONLY | Opening pressure, CSF analysis, tap test for NPH | Absolutely contraindicated in non-communicating hydrocephalus [1] |
| EVD [1] | Acute, non-communicating, or unstable/evolving | Continuous ICP monitoring + therapeutic CSF drainage | Invasive; infection risk ~5–10% |
| Cranial USS | Infants with open fontanelle | Ventricular dilatation | Non-invasive, no radiation |
| Shunt series XR | Shunted patients with new symptoms | Disconnection, fracture, migration of catheter | Non-invasive |
| Fundoscopy | All suspected raised ICP | Papilloedema (late sign) | Non-invasive |
| Contrast MRI/CT | Aetiological workup | Tumour, meningeal enhancement, abscess | Contrast allergy risk; gadolinium for MRI |
High Yield Summary
Diagnosis of hydrocephalus rests on:
- Clinical suspicion — raised ICP symptoms OR NPH triad
- Imaging — ventriculomegaly (Evans' index > 0.3) with disproportionate sulcal effacement and periventricular oedema (best seen on T2-FLAIR)
- CSF dynamics — LP (communicating only), MRI CSF flow studies, EVD
Critical safety rule: No LP if raised ICP unless absolutely sure communicating hydrocephalus [1]
Distinguishing true hydrocephalus from ex vacuo: ventriculomegaly >> sulcal widening in true hydrocephalus; proportional enlargement in atrophy
NPH diagnosis: Evans' index > 0.3 + DESH sign + periventricular FLAIR signal + positive CSF tap test (clinical improvement after removing 30-50 mL CSF)
First ventricle to dilate: temporal horn of lateral ventricles [3]
Pattern helps localise obstruction: all ventricles dilated = communicating; 4th ventricle normal = obstruction at or above the aqueduct
ICP monitoring: EVD is gold standard; threshold to intervene > 20 cmH₂O [1]
For shunted patients with new symptoms: urgent CT brain + shunt series XR to assess for blockage, disconnection, or overdrainage [3]
Active Recall - Hydrocephalus Diagnosis and Investigations
[1] Lecture slides: GC 111. Raised intracranial pressure and hydrocephalus.pdf (p1–2, p9, p14–18) [3] Senior notes: maxim.md (Section 5.3 Hydrocephalus) [5] Senior notes: Ryan Ho Neurology.pdf (p153, p159–160) [6] Senior notes: Ryan Ho Opthalmology.pdf (p90) [7] Senior notes: Ryan Ho Respiratory.pdf (p79) [8] Senior notes: Ryan Ho Radiology.pdf (p20–21) [9] Lecture slides: GC 109. Headache and loss of consciousness Acute stroke, subarachnoid haemorrhage and vascular malformation.pdf (p20–21) [11] Senior notes: Ryan Ho Psychiatry.pdf (p82) [13] Senior notes: Ryan Ho Neurology.pdf (p145) [13a] Senior notes: maxim.md (Section on intracranial tumours)
The management of hydrocephalus follows a logical hierarchy built around three fundamental goals articulated in the lecture slides [1]:
The Fundamentals [1]:
- Protect uninjured brain
- Salvage injured brain
- Treat underlying cause
And within that framework, the overarching priorities are [1]:
- ALWAYS resuscitate first — ABC before ICP [1]
- Clinical/ICP monitoring
- Control ICP and maintain cerebral perfusion
- Neuroprotective therapies
Think of hydrocephalus management as a time-ordered cascade: you stabilise the patient first (ABC), buy time with temporising measures, then move to definitive treatment of both the hydrocephalus and its underlying cause.
Treatment Modalities — Detailed Breakdown
"ABC first" — "ALWAYS resuscitate first" [1]
Before doing anything about the ICP, you must ensure the patient is haemodynamically stable, ventilating adequately, and oxygenating well. This is because:
- Hypotension → ↓ MAP → ↓ CPP (CPP = MAP − ICP) → worsening cerebral ischaemia
- Hypoxia → direct neuronal injury + cerebral vasodilation (to compensate) → ↑ cerebral blood volume → ↑ ICP
- Hypercarbia → cerebral vasodilation → ↑ blood volume → ↑ ICP
Practical steps:
- Airway: Intubate if GCS ≤ 8 (cannot protect airway) [1]
- Breathing: Target SpO₂ > 97%, PaO₂ > 9 kPa, PaCO₂ 4.5–5 kPa [3]
- Circulation: Maintain adequate MAP for CPP (~60–80 mmHg) [1]. Avoid hypotension
- Head elevation: 30° — promotes venous drainage from the cranium (reduces intracranial venous blood volume → ↓ ICP) [3]
- Loosen neck constraints — tight cervical collars or lines can compress the jugular veins → impede venous outflow → ↑ ICP [3]
Phase 2: Temporising Measures
These buy time while you work towards definitive treatment. The choice depends critically on whether the hydrocephalus is communicating or non-communicating [1].
"LP if communicating" [1]
| Aspect | Details |
|---|---|
| Indication | Communicating hydrocephalus where CSF drains freely between ventricles and lumbar subarachnoid space [1][5] |
| Contraindication | LP is absolutely contraindicated (and lethal) in non-communicating hydrocephalus [1]. Also contraindicated if any suspicion of posterior fossa mass or uncal herniation |
| Mechanism | Removing 30–50 mL of CSF from the lumbar space → reduces total CSF volume → immediate ↓ ICP. Because the system is communicating, pressure reduction is transmitted uniformly to the ventricles [5] |
| Practical | Removal of 30–40 mL of CSF [5]; measure opening pressure; send CSF for analysis if aetiology unclear |
| Why it's dangerous in non-communicating HC | If there is a block within the ventricular system, removing CSF below the block creates a transtentorial pressure gradient: high pressure above (ventricles) vs low pressure below (lumbar) → downward herniation of the brainstem through the foramen magnum → death |
"No LP if raised ICP unless absolutely sure communicating hydrocephalus" [1]
"EVD if doubt or unstable/evolving condition" [1]
| Aspect | Details |
|---|---|
| What it is | A small catheter inserted through a burr hole into the lateral ventricle (usually via Kocher's point: 11 cm posterior from nasion, 3 cm lateral to midline), connected to a closed external drainage system [1][5] |
| Dual function | Manometric principle for monitoring intracranial CSF pressure + Therapeutic by draining CSF for decompression [1] |
| Indications | Any acute hydrocephalus where LP is contraindicated or unsafe; non-communicating hydrocephalus; unstable patient; evolving condition where continuous ICP monitoring is needed; "EVD — rarely" for diagnosis but commonly for treatment [1] |
| Advantages | Can be used in BOTH communicating and non-communicating hydrocephalus (unlike LP). Allows continuous monitoring. Can be clamped/opened to titrate drainage |
| Risks | Risk of infection (~5–10%), iatrogenic trauma, haemorrhage during insertion, overdrainage [1][3] |
| Temporary only | EVD is a temporary measure only but allows monitoring [5] — it is a bridge to definitive treatment, not a permanent solution |
How EVD works from first principles: By placing a catheter directly into the dilated ventricle, you bypass any obstruction (the drain is upstream of any block). CSF drains into an external bag, reducing ventricular volume and ICP. The height of the drainage bag relative to the external auditory meatus sets the drainage pressure — lower bag = more drainage (but risk of overdrainage); higher bag = less drainage.
Acetazolamide + Furosemide [3]
| Drug | Mechanism | Role |
|---|---|---|
| Acetazolamide ("Diamox") | Carbonic anhydrase inhibitor → ↓ HCO₃⁻ and Na⁺ secretion by choroid plexus → ↓ CSF production (can reduce production by ~50%) | Temporary measure to slow CSF accumulation while planning definitive treatment |
| Furosemide (frusemide) | Loop diuretic → ↓ total body water → ↓ CSF formation via reduced water availability; may also directly inhibit choroid plexus Na⁺/K⁺ transport | Adjunct to acetazolamide |
Limitations: These are temporising measures only — they slow CSF production but do not fix the underlying obstruction or absorption problem. They are most useful in slowly progressive communicating hydrocephalus or post-haemorrhagic hydrocephalus in neonates where definitive surgery is being planned.
Contraindications/Cautions:
- Acetazolamide: metabolic acidosis, renal stones, hypokalemia, sulfonamide allergy
- Furosemide: dehydration, electrolyte derangement, hypovolaemia
While these are not specific to hydrocephalus, they form part of the overall management of any patient with raised ICP [1][3]:
| Measure | Mechanism | Important Caveats |
|---|---|---|
| Head elevation 30° | Promotes venous drainage from the cranium via gravity → ↓ intracranial venous blood volume → ↓ ICP | Ensure the neck is neutral (not rotated/flexed) to avoid jugular compression |
| Sedation and analgesia | ↓ Metabolic demand → ↓ cerebral blood flow requirement → ↓ ICP. Also prevents agitation-induced ICP spikes | Use in ICU setting with ICP monitoring |
| IV Mannitol (0.25–1 g/kg bolus) | Osmotic diuretic → creates osmotic gradient drawing water from brain parenchyma into blood → ↓ brain volume → ↓ ICP. Onset 15 min, duration ~6h | "No mannitol if shocked" [1] — mannitol causes osmotic diuresis → hypovolaemia → worsens shock. Avoid if serum Na > 155 or osmolality > 320 mOsm/L |
| Hypertonic saline (3% or 23.4%) | Similar osmotic mechanism to mannitol but without diuretic effect → can be used in hypovolaemic patients | Alternative to mannitol; monitor sodium levels |
| Controlled hyperventilation | ↓ PaCO₂ → cerebral vasoconstriction → ↓ cerebral blood volume → ↓ ICP | "No prophylactic/prolonged/uncontrolled hyperventilation" [1]. Short-term bridge only (target PaCO₂ 30–35 mmHg). Prolonged use causes rebound vasodilation and can worsen ischaemia |
| Steroids (dexamethasone) | ↓ Vasogenic oedema around tumours by stabilising BBB | "Steroids for tumour but not TBI or stroke" [1]. C/I in suspected CNS lymphoma (destroys diagnostic yield) [5a] |
The Do-NOT-Do List — From Key Messages
Straight from the lecture slides [1]:
- No mannitol if shocked
- No prophylactic/prolonged/uncontrolled hyperventilation
- No LP if raised ICP unless absolutely sure communicating hydrocephalus
- Steroids for tumour but not TBI or stroke
- ABC before ICP
Phase 3: Definitive Treatment
Treatment of Hydrocephalus — Definitive measures [1]:
- CSF shunting (e.g., ventriculo-peritoneal, ventriculo-atrial)
- Endoscopic third ventriculostomy
- Treat underlying cause (e.g., haematoma/tumour removal)
This is conceptually the most important step — if you can remove the cause of the hydrocephalus, you may not need permanent CSF diversion at all.
| Cause | Definitive Treatment |
|---|---|
| Posterior fossa tumour | Craniotomy for haematoma/tumour removal [1] — once the tumour compressing the 4th ventricle is removed, CSF pathways may re-open |
| Colloid cyst of 3rd ventricle | Surgical excision (endoscopic or open) |
| SAH | Secure aneurysm (clip or coil) [14] to prevent rebleeding, then manage hydrocephalus (may resolve after blood clears; if not → shunt) |
| Meningitis | Appropriate antimicrobials (antibiotics for bacterial, anti-TB for TBM, antifungals for cryptococcal) |
| Cerebellar haemorrhage | Evacuation of hematoma if brainstem compression, haematoma > 3 cm, or obliteration of cisterns; external ventricular drainage if small haematoma with hydrocephalus [15] |
| Choroid plexus papilloma | Surgical excision → removes the source of CSF overproduction |
Post-SAH hydrocephalus deserves special mention [14]:
- Acute increase in ICP — CSF drainage helps but might provoke re-bleeding if aneurysm not yet secured! [14]
- Delayed — poor absorption and usually communicating — for shunting [14]
- Beware of new symptoms several months post-SAH [14] — delayed hydrocephalus can present weeks to months later as gradual cognitive decline, gait difficulty, incontinence
B. CSF Shunting — Permanent CSF Diversion
When the underlying cause cannot be removed or hydrocephalus persists despite treating the cause, permanent CSF diversion is needed.
| Shunt Type | Route | When to Use | Specific Considerations |
|---|---|---|---|
| Ventriculo-peritoneal (VP) shunt | Lateral ventricle → subcutaneous tunnel → peritoneal cavity | Usually 1st choice [5] — peritoneal cavity has large absorptive surface area | Most common; easiest to revise. C/I: peritonitis, peritoneal adhesions, abdominal surgery, ascites |
| Ventriculo-atrial (VA) shunt | Lateral ventricle → subcutaneous tunnel → right atrium (via internal jugular/facial vein) | When peritoneal cavity is unsuitable (e.g., adhesions, prior peritonitis) | Risk of nephritis (VA) [1] (immune complex glomerulonephritis from chronic bacteraemia — "shunt nephritis"), atrial arrhythmia, pulmonary embolism |
| Lumbo-peritoneal (LP) shunt | Lumbar subarachnoid space → peritoneal cavity | Communicating hydrocephalus only (CSF must freely reach the lumbar space) | Avoids cranial surgery. Risks: tonsillar herniation if used in non-communicating HC (same principle as LP contraindication), overdrainage, radiculopathy |
A shunt system has three parts:
- Ventricular (proximal) catheter — sits within the lateral ventricle (usually the frontal horn)
- Valve and reservoir — a one-way valve to control CSF flow [1]. Prevents backflow and regulates the drainage pressure. The reservoir can be palpated subcutaneously behind the ear and can be percutaneously aspirated ("shunt tap") to test function or obtain CSF
- Distal catheter — tunnelled subcutaneously to the peritoneal cavity (VP), right atrium (VA), or from the lumbar space to peritoneum (LP)
Programmable CSF shunt — a critically important modern advance:
- Allows post-op transcutaneous adjustment of shunt valve setting [1]
- Tailored to individual patients' needs [1]
- Affected by external magnetic field [1]
- Check before and after MRI [1][5]
How it works: The valve contains a small magnetic mechanism that sets the opening pressure. Using an external magnetic programmer held over the scalp, the clinician can non-invasively increase or decrease the drainage pressure after surgery. This avoids the need for reoperation if the drainage rate needs adjusting (e.g., if there's overdrainage causing CSDH, you increase the valve setting; if there's underdrainage with persistent hydrocephalus, you decrease it).
Important: MRI scanners generate powerful magnetic fields → can inadvertently reset the programmable valve setting. Therefore: check setting before and after MRI [1][5]. Modern programmable valves (e.g., Codman Certas Plus, Medtronic Strata) are increasingly MRI-resistant but always verify.
NOT C/I for MRI, but need to check setting before and after MRI [5]
Endoscopic Third Ventriculostomy (ETV) [1]
| Aspect | Details |
|---|---|
| Concept | Fenestrate 3rd ventricle floor → bypass obstruction and restore CSF flow [1]. A neuroendoscope is passed through the lateral ventricle into the 3rd ventricle, and a hole is made in the floor of the 3rd ventricle (the tuber cinereum). This creates a direct communication between the 3rd ventricle and the prepontine cistern (subarachnoid space), bypassing the obstructed aqueduct |
| Indication | Obstructive hydrocephalus — specifically when the obstruction is at or distal to the aqueduct of Sylvius [1][2]. The 3rd ventricle must be dilated enough to safely perform the procedure. Classic scenario: pineal tumour with 3rd ventricle blockage → can shunt or do ETV [1] |
| Contraindication | NOT communicating hydrocephalus [2] — because in communicating hydrocephalus, the problem is impaired absorption at the arachnoid granulations, not a flow obstruction within the ventricular system. Creating a hole in the 3rd ventricle floor won't help if the subarachnoid absorption is the problem |
| Advantages | Avoid permanent shunting [1] — no implanted hardware, no risk of shunt infection/malfunction/overdrainage; Enable tumour biopsy [1] — the same endoscopic procedure can biopsy an obstructing tumour for histological diagnosis |
| Success rate | ~70–80% in appropriately selected patients (aqueductal stenosis, posterior fossa tumours). Lower success in infants < 6 months (immature arachnoid granulations may limit absorption even if flow is restored) |
| Complications | Basilar artery injury (the floor of the 3rd ventricle lies directly above the basilar artery), ventriculitis, CSF leak, hypothalamic injury, memory impairment (fornix damage) |
ETV vs Shunting — When to Choose What?
Why ETV Does NOT Work for Communicating Hydrocephalus
This is a concept often tested. In communicating hydrocephalus, CSF flows freely from the ventricles into the subarachnoid space — the problem is at the arachnoid granulations (impaired absorption). ETV creates a bypass from the 3rd ventricle to the subarachnoid space — but the CSF is already getting to the subarachnoid space just fine. The bottleneck is downstream at absorption. Therefore, ETV does not address the pathology and is contraindicated [2][5].
NPH responds well to CSF diversion (e.g., VP-shunting) [1]
The management of NPH is unique because:
- There is no acute emergency (ICP is normal)
- The challenge is diagnostic certainty — you want to be confident that the patient will improve with shunting before subjecting them to surgery
- Need to distinguish from other causes of dementia such as AD, which does not respond to shunting [1]
NPH Management Protocol:
- Confirm diagnosis: imaging (ventricular enlargement >> sulcal effacement, FLAIR hyperintensity), tap test (remove 30–50 mL CSF, assess gait and cognition improvement) [5]
- If tap test positive: proceed to VP shunt (usually with programmable valve for post-op titration)
- If tap test equivocal: extended lumbar drainage over 72 hours → reassess
- Post-shunt follow-up: regular CT to assess adequacy of shunting [5], clinical assessment of triad symptoms, check programmable valve setting after any MRI
Prognosis of NPH after shunting:
- Gait: improves in ~80–90% of patients — the most responsive component
- Cognition: improves in ~50–70%
- Incontinence: improves in ~50–60%
- Best outcomes when gait disturbance is the predominant feature (correlating with the mechanism — periventricular motor fibre compression is the most directly reversible pathology)
- Poorer outcomes with longer symptom duration, more advanced dementia, or significant comorbid cerebrovascular disease
After any intervention for hydrocephalus:
- Regular follow-up CT to assess adequacy of shunting/ventricular size [5]
- Clinical assessment of symptoms at each visit
- Shunt setting check after any MRI (for programmable shunts) [1][5]
- Vigilance for shunt complications (see Complications section to follow)
- Serial head circumference in infants
These are high-yield exam scenarios directly from the lecture:
| Scenario | What to Suspect | Action |
|---|---|---|
| 1. Recurrent hydrocephalic symptoms | Blocked shunt? | Test shunt if you know what you are doing [1] — urgent CT brain + shunt series XR |
| 2. Raised ICP symptoms ± focal deficit | CSDH? (e.g., elderly on aspirin) [1] | CT brain — crescentic extra-axial collection; neurosurgical evacuation |
| 3. Postural headache (worse when erect) | Intracranial hypotension? (e.g., over-shunting without CSDH) [1] | Adjust programmable valve to higher setting; contrast MRI may show diffuse pachymeningeal enhancement, sagging brain |
| 4. Fever + abdominal pain | Shunt infection causing peritonitis? OR Peritonitis causing shunt infection? [1] | Externalise shunt + antibiotics [1] — remove the infected distal catheter from the peritoneum and convert to an external drain while treating the infection; then re-internalise once infection cleared |
Avoid Shunting If Possible
"Avoid shunting if possible!" [1] — This is a direct message from the lecture slides. Every implanted shunt carries lifelong risks of infection, malfunction, and revision surgery. When an alternative exists (e.g., ETV for obstructive hydrocephalus, treating the underlying cause directly), it should be preferred. However, when shunting is necessary, it is a well-established and effective treatment.
| Treatment | Type | Indication | Contraindication | Key Point |
|---|---|---|---|---|
| LP drainage | Temporising | Communicating HC | Non-communicating HC (lethal) [1] | Safe, quick, diagnostic + therapeutic |
| EVD | Temporising | Any HC type, unstable patient | Awake patients, coagulopathy (relative) | Gold standard for ICP monitoring + drainage |
| Acetazolamide + furosemide | Medical | Slowly progressive HC, bridge to surgery | Metabolic acidosis, dehydration | ↓ CSF production; temporary only |
| VP shunt | Definitive | Communicating HC, NPH, any HC needing permanent diversion | Peritonitis, ascites, peritoneal adhesions | Usually 1st choice [5]; programmable valve preferred |
| VA shunt | Definitive | When peritoneum unsuitable | Cardiac disease, chronic bacteraemia | Risk of shunt nephritis, arrhythmia |
| LP shunt | Definitive | Communicating HC only | Non-communicating HC | Avoids craniotomy; risk of tonsillar herniation |
| ETV | Definitive | Obstructive HC | Communicating HC [2] | Avoids permanent shunting, enables tumour biopsy [1] |
| Tumour/haematoma removal | Definitive (cause) | Obstructing mass | Inoperable location/patient | May resolve HC without needing shunt |
| Decompressive craniectomy | Last resort | Massive infarction, post-TBI swelling | Not for HC specifically | Primary pathology (deficit) unchanged; quality of survival variable [1] |
High Yield Summary
Management hierarchy: ABC first → Temporise → Definitive treatment → Treat underlying cause
Temporising measures:
- LP if communicating (NEVER in non-communicating — lethal)
- EVD if doubt or unstable/evolving condition — works for any type; also monitors ICP
- Medical: acetazolamide + furosemide (↓ CSF production — bridge only)
Definitive measures:
- CSF shunting: VP shunt (1st choice), VA shunt (if peritoneum unsuitable), LP shunt (communicating only)
- ETV: for obstructive HC only — fenestrates 3rd ventricle floor, avoids permanent shunting, enables tumour biopsy. NOT for communicating HC
- Treat underlying cause: tumour removal, aneurysm clipping/coiling, antibiotics for meningitis
Programmable shunts: allow transcutaneous adjustment; must check before and after MRI
NPH: responds well to VP shunting; gait improves most reliably; positive tap test predicts good shunt response
Key safety rules: No LP if non-communicating; no mannitol if shocked; no uncontrolled hyperventilation; steroids for tumour only (not TBI/stroke); avoid shunting if possible
Post-SAH hydrocephalus: CSF drainage helps acutely but may provoke rebleeding if aneurysm not yet secured; delayed hydrocephalus is usually communicating → shunting
Active Recall - Hydrocephalus Management
[1] Lecture slides: GC 111. Raised intracranial pressure and hydrocephalus.pdf (p8–9, p13–18) [2] Senior notes: felixlai.md (Hydrocephalus treatment section) [3] Senior notes: maxim.md (Section 5.3 Hydrocephalus; ICP management section) [5] Senior notes: Ryan Ho Neurology.pdf (p156, p159–160, p163) [5a] Senior notes: Ryan Ho Neurology.pdf (p163 — steroids C/I in CNS lymphoma) [14] Lecture slides: GC 109. Headache and loss of consciousness Acute stroke, subarachnoid haemorrhage and vascular malformation.pdf (p20) [15] Lecture slides: Cererbrovascular disease.pdf (p10 — cerebellar haemorrhage management)
Complications of hydrocephalus fall into two broad categories: complications of the disease itself (untreated or inadequately treated hydrocephalus) and complications of treatment (predominantly CSF shunt-related complications). The treatment-related complications are arguably more commonly tested in exams, because a large proportion of hydrocephalus patients live with shunts for years or decades, and shunt complications are everyday neurosurgical emergencies.
A. Complications of the Disease Itself
This is the most feared and immediately life-threatening complication of untreated or rapidly progressive hydrocephalus.
When ICP rises, pressure gradients develop across the dural compartments (falx cerebri, tentorium cerebelli). Brain tissue is pushed from high-pressure compartments to low-pressure compartments through rigid openings — this is herniation.
| Type | Mechanism | Clinical Features |
|---|---|---|
| Uncal (transtentorial) herniation | The medial temporal lobe (uncus) herniates through the tentorial notch → compresses the ipsilateral CN III against the posterior clinoid process, then the ipsilateral cerebral peduncle, then the brainstem | Ipsilateral fixed dilated pupil → contralateral hemiparesis → ↓ consciousness → Cushing's triad → death |
| Central (downward transtentorial) herniation | Midline or bilateral supratentorial mass → diencephalon pushed inferiorly through tentorial hiatus | Bilateral small pupils → Cheyne-Stokes respiration → progressive ↓ consciousness → bilateral dilated pupils (midbrain stage) |
| Tonsillar (cerebellar) herniation ("coning") | Posterior fossa mass or diffuse raised ICP → cerebellar tonsils herniate through the foramen magnum → compress medulla | Cardiorespiratory arrest, loss of consciousness, bilateral dilated pupils, decerebrate/decorticate posturing [5] |
| Subfalcine (cingulate) herniation | Unilateral supratentorial mass → cingulate gyrus herniates under the falx cerebri → compresses the anterior cerebral artery | Bilateral leg weakness (ACA territory ischaemia) [5] |
Why is tonsillar herniation so lethal? The medulla contains the cardiovascular and respiratory centres. Compression of these nuclei causes immediate cardiorespiratory arrest — there is essentially no warning and no time to intervene once it occurs.
Untreated hydrocephalus causes progressive, ultimately irreversible brain injury through several mechanisms:
- Periventricular white matter ischaemia: Expanded ventricles compress periventricular capillaries → chronic ischaemia → demyelination and gliosis
- Cortical compression: Especially in infants where the skull expands but the brain is thinned against the inner table
- Developmental delay and intellectual disability (in children): Chronic compression during critical periods of brain development → mental retardation, cerebral palsy [5][7]
- Visual loss: Chronic papilloedema → optic atrophy → permanent blindness [6]. Also, direct compression of the optic chiasm by a dilated 3rd ventricle [7]
Occur in ~10% of patients with hydrocephalus. Mechanisms include:
- Cortical irritation from periventricular oedema spreading to the cortex
- Cortical ischaemia from impaired perfusion
- Co-existing pathology (e.g., meningitis, tumour, haemorrhage)
B. Complications of CSF Shunt — The High-Yield Section
"Avoid shunting if possible!" [1] — and the reason for this emphatic statement is the following list of complications. Every shunt is a lifelong implant that requires regular monitoring. The lecture slides list these complications explicitly [1]:
- Infection (1° or 2°)
- Blockage → hydrocephalus
- Dislodgement/Fracture → hydrocephalus
- Over-shunting → CSDH
- Abdominal pseudocyst
- Slit ventricle syndrome
- Nephritis (VA)
- Bowel perforation (VP) …
Let's break each one down from first principles.
"Infection (1° or 2°)" [1]
| Aspect | Details |
|---|---|
| Incidence | ~5–15% per procedure; highest risk in the first 1–2 months post-insertion |
| Pathogens | S. epidermidis (most common — skin commensal colonises the shunt hardware during insertion), S. aureus [3] |
| Mechanism | Primary (1°): contamination during surgery → organisms adhere to the shunt surface, form a biofilm, and proliferate. Secondary (2°): haematogenous seeding from another infection, or retrograde infection from the distal end (e.g., peritonitis tracking up a VP shunt) |
| Clinical features | Fever, lethargy, meningism, S/S of raised ICP [3] (from ventriculitis and shunt blockage by inflammatory debris). Abdominal distension and tenderness if peritonitis (VP shunt). Cutaneous erythema along the shunt tract [3] |
| Investigations | Contrast CT brain (ventriculomegaly suggesting blockage, enhancing ependyma suggesting ventriculitis); inspect entire course of shunt for cutaneous erythema [3]; shunt tap (aspirate CSF from the reservoir) for cell count, culture, and Gram stain; blood cultures |
| Management | Infected shunts must be removed [5] — antibiotics alone cannot sterilise a biofilm on hardware. The protocol is: remove the entire shunt system → insert a temporary EVD for CSF diversion (bridge for ~4–6 weeks) [5] → IV antibiotics (usually vancomycin + ceftriaxone or tailored to culture) → once CSF is sterile for at least 48–72 hours, re-internalise with a new shunt |
The lecture slides highlight a common scenario: "Fever + abdominal pain → Shunt infection causing peritonitis? Peritonitis causing shunt infection? → Externalise shunt + antibiotics" [1]
Why is infection so feared? Because:
- Ventriculitis (infection of the ventricular lining) is extremely difficult to treat — the blood-brain barrier limits antibiotic penetration
- Biofilms on shunt hardware are inherently resistant to antibiotics (bacteria in biofilms are ~1000× more resistant than planktonic bacteria)
- Repeated infections and revisions damage the brain and reduce future treatment options
Key Exam Concept — Primary vs Secondary Shunt Infection
Primary infection: Introduced during the shunt surgery itself (skin organisms contaminate the hardware). This is why strict aseptic technique, antibiotic-impregnated catheters, and perioperative antibiotics are essential.
Secondary infection: The shunt becomes infected from another source — e.g., abdominal peritonitis in VP shunt (ascending infection from the distal catheter), bacteraemia from a distant focus, or wound breakdown over the shunt tract. This bidirectional relationship is highlighted in the lecture slides: "Shunt infection causing peritonitis? Peritonitis causing shunt infection?" [1]
"Blockage → hydrocephalus" [1]
| Aspect | Details |
|---|---|
| Incidence | The most common complication overall; ~40% of shunts malfunction within the first year, ~80% within 10 years |
| Site of blockage | 80% proximal (ventricular catheter) , 10% valve, 10% distal catheter [3] |
| Causes of proximal blockage | Choroid plexus, brain parenchyma, protein, tumour cells [3] — the choroid plexus is like seaweed; it can wrap around and occlude the catheter tip. Brain tissue can also grow into the catheter holes. In patients with high CSF protein (e.g., post-meningitis, post-haemorrhage), proteinaceous debris plugs the fenestrations |
| Causes of distal blockage | Omental wrapping (VP), fibrin sheath, pseudocyst formation |
| Clinical features | Recurrence of hydrocephalus symptoms: headache, vomiting, drowsiness, ↓ GCS — "Recurrent hydrocephalic symptoms → Blocked shunt?" [1]. Symptoms may be stereotypical for each patient — "S/S stereotypical (ask the patient, may be variable)" [5] |
| Investigations | Urgent CT brain (compare with previous — are ventricles larger?) + shunt series (plain XR of entire shunt: skull XR, C-spine XR, CXR, AXR) [3] |
| Management | Consult NS for shunt revision [3] — usually involves replacing the obstructed component |
Important clinical pearl on testing shunt function [5]:
- Valve pumping is NOT accurate, not sensitive, not specific [5]
- Do NOT pump (will over-shunt CSF) [5]
- Can press once to differentiate between distal and proximal obstruction [5]: The shunt reservoir sits between two one-way valves. If you press the reservoir and it does not refill → proximal blockage (nothing coming from the ventricle). If you press and it does not empty (remains full) → distal blockage (nothing draining downstream)
- Shuntogram (inject radiopaque contrast into the shunt) can confirm the site of blockage [5]
"Dislodgement/Fracture → hydrocephalus" [1]
| Aspect | Details |
|---|---|
| Mechanism | The catheter is a long, thin silicone tube running from the skull to the abdomen (VP) or heart (VA). Over time, particularly in growing children, the catheter can migrate out of position, fracture from repeated mechanical stress, or disconnect at junction points |
| In children | Growth of the child "outgrows" the catheter — the distal catheter gradually pulls out of the peritoneal cavity as the child grows taller → loss of drainage capacity. This is why paediatric patients require periodic shunt revisions |
| Detection | Shunt series (plain XR) demonstrates the break, disconnection, or catheter tip in wrong position |
| Management | Surgical revision — replace the fractured/migrated component |
"Over-shunting → CSDH" [1]
This is one of the most important and commonly tested complications.
| Aspect | Details |
|---|---|
| Mechanism | Excessive CSF drainage → ventricular collapse → the brain "sinks" away from the inner skull table → bridging veins (which span from the cortical surface to the dural venous sinuses) are stretched → tearing of bridging veins → subdural haematoma [3][5] |
| Clinical features | Two distinct presentations: (1) Postural headache (worsened with standing/sitting, relieved when lying down) [1][3] — this is intracranial hypotension from excessive drainage, where the brain sags under gravity when upright; (2) Raised ICP symptoms ± focal deficit → CSDH? (e.g., elderly on aspirin) [1] — when the subdural collection becomes large enough, it acts as a mass lesion causing raised ICP itself |
| Investigations | CT brain: uni- or bilateral crescentic extra-axial collections (hypodense if chronic, mixed density if acute-on-chronic) |
| Management | If postural headache without CSDH: increase the programmable valve pressure setting (reduce drainage rate) [5]. If significant CSDH: neurosurgical evacuation via burr hole drainage |
Why does this happen? From first principles: CSF provides buoyancy to the brain (the brain weighs ~1500g in air but only ~50g when floating in CSF). Over-shunting removes this buoyancy → the brain drops downward → stretches the bridging veins that tether it to the skull → these veins have thin walls and no valves → they tear, creating a slow subdural bleed.
"Raised ICP symptom +/- focal deficit → CSDH? (e.g., elderly on aspirin)" [1] — This is a common clinical scenario from the lecture slides. Elderly patients on antiplatelet/anticoagulant therapy are at particularly high risk because their coagulation is impaired, amplifying any bridging vein tear.
"Abdominal pseudocyst" [1]
| Aspect | Details |
|---|---|
| What it is | An intraperitoneal CSF-filled pseudocyst [3] — a walled-off collection of CSF within the peritoneal cavity, surrounded by a fibrous capsule (not a true cyst, hence "pseudo" = false) |
| Mechanism | Low-grade chronic infection or inflammation around the distal VP catheter tip → peritoneal surfaces become inflamed and form adhesions → CSF becomes trapped in a loculated pocket rather than being absorbed by the peritoneal surfaces |
| Clinical features | Abdominal pain, distension, palpable abdominal mass, ± shunt malfunction (the pseudocyst raises back-pressure, preventing CSF drainage → recurrent hydrocephalus symptoms) |
| Investigations | Abdominal ultrasound or CT abdomen — fluid-filled cystic mass surrounding the distal catheter tip |
| Management | Drain the pseudocyst; revise the distal catheter to a different peritoneal site or convert to VA shunt; send fluid for culture to rule out infection |
"Slit ventricle syndrome" [1]
| Aspect | Details |
|---|---|
| What it is | A rare but dreaded long-term complication of CSF shunting, particularly in patients shunted in childhood |
| Mechanism | Chronic long-term over-drainage changes the compliance of the brain and ventricular walls [5]. The ventricles become very small ("slit-like") and the brain becomes stiff. If the shunt then blocks, the ventricles cannot re-expand despite markedly elevated ICP → "nightmare scenario: long-term shunting changes compliance of brain and ventricles → ventricles do not dilate despite ↑↑↑ ICP" [5] |
| Clinical features | Intermittent severe headaches (often positional). The danger: if shunt blocks, the patient develops markedly raised ICP but the CT scan may look near-normal (slit ventricles look the same whether the shunt is working or not) → the diagnosis is easily missed |
| Investigations | Compare carefully with previous CT for subtle enlargement → blockage [5]. Even a tiny increase in ventricular size from a baseline of "slit" ventricles may indicate significant obstruction |
| Management | Extremely challenging — may require subtemporal decompression, shunt revision, or conversion to a programmable valve. Prevention is key: avoid chronic overdrainage from the outset |
The Slit Ventricle Trap
The greatest danger of slit ventricle syndrome is diagnostic delay. In a normal patient with shunt blockage, CT shows obvious ventriculomegaly and the diagnosis is straightforward. In slit ventricle syndrome, the ventricles cannot expand → CT looks deceptively normal → the clinician may falsely reassure the patient while ICP is dangerously elevated. Always compare with prior imaging and maintain a high index of suspicion in chronically shunted patients with headaches [5].
"Nephritis (VA)" [1]
| Aspect | Details |
|---|---|
| What it is | Immune complex glomerulonephritis ("shunt nephritis") — a unique complication of ventriculo-atrial shunts |
| Mechanism | Chronic low-grade bacteraemia from colonisation of the intravascular (atrial) catheter tip → persistent antigenaemia → formation of immune complexes (antigen-antibody) → deposition in glomerular basement membrane → complement activation → membranoproliferative or membranous glomerulonephritis |
| Clinical features | Haematuria, proteinuria, nephrotic syndrome, renal impairment, ± fever, splenomegaly |
| Why this doesn't happen with VP shunts | The peritoneal cavity is an extravascular space — even if bacteria colonise the catheter, they don't enter the bloodstream to cause systemic immune complex disease. The atrial catheter sits directly in the blood → direct access for chronic bacteraemia |
| Management | Remove the infected VA shunt, treat the infection, convert to VP shunt if possible. Renal involvement may be partially reversible with infection control |
"Bowel perforation (VP)" [1]
| Aspect | Details |
|---|---|
| Mechanism | The distal catheter sits free within the peritoneal cavity. Over time, chronic pressure from the rigid catheter tip against a loop of bowel → erosion → perforation. This can also occur during initial insertion if the trocar used to pass the catheter into the peritoneum inadvertently punctures bowel |
| Clinical features | Peritonitis (abdominal pain, fever, rigidity, absent bowel sounds), or insidious presentation with protrusion of catheter through the anus (rare but reported) |
| Management | Surgical: remove the distal catheter from the perforated bowel, repair the bowel, externalise the shunt, treat peritonitis with broad-spectrum antibiotics, re-internalise after resolution |
- Inguinal hernia: Increased intraperitoneal pressure from CSF fluid within the peritoneal cavity → weakens the inguinal canal → hernia. More common in infants (patent processus vaginalis)
- CSF ascites: Excessive CSF drainage overwhelms peritoneal absorptive capacity
- Tumour seeding: In patients with CNS malignancies (medulloblastoma, ependymoma, choroid plexus carcinoma), the shunt can act as a conduit for tumour cells to metastasise from the ventricle to the peritoneum [3] — so-called "shunt metastasis." This is rare but important in paediatric neuro-oncology
While ETV avoids the lifelong complications of shunts, it has its own risks:
| Complication | Mechanism |
|---|---|
| Basilar artery injury | The floor of the 3rd ventricle lies directly above the basilar artery. During fenestration, the endoscope or perforating instrument can injure the basilar artery → catastrophic subarachnoid haemorrhage |
| Ventriculitis / meningitis | Introduction of infection during the endoscopic procedure |
| CSF leak | Through the burr hole site |
| Hypothalamic injury | The hypothalamus forms the lateral walls and floor of the 3rd ventricle → thermal or mechanical injury during the procedure |
| Stoma closure | The fenestration in the 3rd ventricle floor can scar over and close weeks to months after the procedure → recurrent hydrocephalus. This occurs in ~10–30% of cases and requires re-do ETV or conversion to shunt |
| Memory impairment | The fornix (part of the memory circuit) passes along the roof of the 3rd ventricle and can be damaged during endoscopic navigation |
| Complication | Mechanism and Details |
|---|---|
| Infection | ~5–10% risk; increases with duration of EVD placement (risk ~2% per day beyond day 5). Pathogens: S. epidermidis, S. aureus, Gram-negatives. Prophylactic: antibiotic-impregnated catheters reduce infection rates [3] |
| Haemorrhage | During insertion: the catheter traverses brain parenchyma → can injure cortical vessels or the choroid plexus → intraventricular or intracerebral haemorrhage |
| Overdrainage | If the external drainage bag is set too low → excessive CSF removal → brain collapse, upward herniation (rare), subdural haematoma |
| Catheter misplacement | The catheter may end up in brain parenchyma rather than the ventricle, particularly if the ventricles are small or in an unusual position due to midline shift |
| Re-bleeding in SAH patients | CSF drainage helps but might provoke re-bleeding if aneurysm not yet secured! [14] — rapid CSF drainage can alter the transmural pressure across the aneurysm wall, promoting re-rupture |
| Scenario | Suspect | Action |
|---|---|---|
| 1. Recurrent hydrocephalic symptoms | Blocked shunt? | Test shunt if you know what you are doing [1] — urgent CT + shunt series |
| 2. Raised ICP symptoms ± focal deficit | CSDH? (e.g., elderly on aspirin) [1] | CT brain → if CSDH present → burr hole evacuation |
| 3. Postural headache (worse when erect) | Intracranial hypotension? (e.g., over-shunting without CSDH) [1] | Adjust programmable valve to higher setting; MRI if symptoms persist |
| 4. Fever + abdominal pain | Shunt infection causing peritonitis? Peritonitis causing shunt infection? [1] | Externalise shunt + antibiotics [1] |
High Yield Summary
Complications of the disease:
- Brain herniation (uncal, central, tonsillar, subfalcine) — life-threatening
- Permanent neurological damage (cognitive, visual, developmental)
- Seizures
- Endocrine disturbance
Complications of CSF shunts (from lecture slides):
- Infection: most serious; S. epidermidis/S. aureus; infected shunts MUST be removed → bridge with EVD + antibiotics
- Blockage: most common (80% proximal); urgent CT + shunt series; NS revision
- Dislodgement/Fracture: detected on shunt series XR
- Over-shunting → CSDH: bridging vein rupture; postural headache or raised ICP from mass effect; adjust programmable valve or surgical evacuation
- Abdominal pseudocyst: CSF-filled loculated collection; infection-related
- Slit ventricle syndrome: chronic over-drainage changes brain compliance; ventricles won't dilate despite high ICP — CT looks deceptively normal
- Nephritis (VA shunt): immune complex glomerulonephritis from chronic bacteraemia
- Bowel perforation (VP shunt): catheter erodes into bowel
ETV complications: basilar artery injury, stoma closure, ventriculitis, hypothalamic/fornix injury
EVD complications: infection (~5-10%), haemorrhage, overdrainage, rebleeding risk in unsecured SAH aneurysms
Key rule: Avoid shunting if possible! [1] — every shunt is a lifelong liability
Active Recall - Complications of Hydrocephalus
[1] Lecture slides: GC 111. Raised intracranial pressure and hydrocephalus.pdf (p14–18) [2] Senior notes: felixlai.md (Hydrocephalus clinical manifestation and treatment sections) [3] Senior notes: maxim.md (Section 5.3 Hydrocephalus — Complications of CSF shunt) [5] Senior notes: Ryan Ho Neurology.pdf (p156, p159–160) [6] Senior notes: Ryan Ho Opthalmology.pdf (p90) [7] Senior notes: Ryan Ho Respiratory.pdf (p79 — TB meningitis complications) [14] Lecture slides: GC 109. Headache and loss of consciousness Acute stroke, subarachnoid haemorrhage and vascular malformation.pdf (p20)
High Yield Summary — Etiology & pathophysiology
Definition: ↑CSF within cranium → ventricular dilatation ± ↑ICP. Not one disease — any disruption of production / flow / absorption.
CSF facts: Total ~150 mL; production ~450–500 mL/day (mostly choroid plexus, carbonic anhydrase dependent). Pathway: lateral → Monro → 3rd → Sylvian aqueduct → 4th → Luschka/Magendie → SAS → arachnoid granulations → venous sinuses.
Aqueduct of Sylvius = narrowest point — common site of obstruction.
Mechanisms: ↑production (rare — choroid plexus papilloma); flow obstruction; ↓absorption (post-SAH, post-meningitis, venous sinus issues).
Monro–Kellie: infants — sutures open → macrocephaly with less ICP rise; adults — rigid skull → ICP rises when compensation exhausted.
NPH: classically "wet, wobbly, wacky" — gait apraxia, incontinence, cognitive decline; surgically treatable dementia if selected carefully.
High Yield Summary — Classification & DDx
Obstructive (non-communicating): Block within ventricles before free SAS communication. Imaging: dilated ventricles proximal to block; 4th ventricle often normal if block supra-aqueductal. LP dangerous → transtentorial pressure gradient → herniation.
Communicating: CSF reaches SAS but absorption impaired (or rarely production overwhelms). LP may be temporising when clearly communicating and safe clinically.
DDx of ventriculomegaly: NPH vs atrophy ("hydrocephalus ex vacuo") vs acute obstructive vs high-volume transependymal oedema. Clinical context + evolution + CSF dynamics studies.
Mimics / associations: Mass colloid cyst (Monro), tectal/pineal compression, tumour haemorrhage, congenital aqueduct stenosis, Chiari.
High Yield Summary — Diagnosis
Imaging: CT first in emergency — ventricular size, transependymal oedema, acute blood, mass. MRI — anatomy, NPH workup, posterior fossa.
↑ICP stigmata: Headache, vomiting, papilloedema, CN VI palsy (false localising), ↓GCS.
NPH: Clinical triad + imaging; large-volume LP or extended lumbar drain trial to predict shunt response.
Key exam principle: If possible obstructive hydrocephalus with mass effect — do not LP until neuroimaging and neurosurgical input.
High Yield Summary — Management
Priorities: ABC first; then control ICP / perfusion; treat underlying cause (clot, tumour, infection, aneurysm).
Acute obstructive / unstable: EVD (external ventricular drain) when doubt, deterioration, or need for ICP/CSF control.
Communicating with ↑ICP: LP may temporise only when obstruction excluded.
Definitive diversion: VP shunt (or VA/LP alternatives); ETV (endoscopic third ventriculostomy) for selected obstructive anatomy (e.g. aqueductal / some posterior fossa pathways).
NPH: Shunt (often programmable) if positive response to CSF removal trial.
Medical adjuncts: Acetazolamide reduces CSF production (selected cases); osmotherapy for acute ICP spikes in context of brain insult — not sole treatment for structural hydrocephalus.
High Yield Summary — Complications
Natural history / untreated obstructive: Rapid ↑ICP → herniation.
Shunt: Infection, obstruction, over-drainage (subdural hygroma, orthostatic headache), under-drainance, seizures, mechanical failure.
EVD: Infection, over-drainage, haemorrhage along tract, need for definitive pathway or conversion to shunt.
LP-related catastrophe: Cerebellar tonsillar herniation if obstructive hydrocephalus mistaken for communicating.
Chronic: Visual failure from chronic papilloedema, gait/cognition if NPH undertreated.
Spinal Cord Injuries
Damage to the spinal cord resulting in temporary or permanent loss of motor, sensory, or autonomic function below the level of injury.
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.